


Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


NNAAMMEE
       Vectors_params - This document briefly describes all
       Vectors internal parameters.

DDEESSCCRRIIPPTTIIOONN
       Parameter descriptions follow, in alphabetical order. Each
       description begins with a line giving the three-character
       mnemonic name of the parameter, the phrase for which the
       mnemonic stands, the intrinsic type of the parameter, and
       an indication of whether or not it is an array.

       ACM - Arrow Color Mode - Integer

	      ACM controls how color is applied to filled vector
	      arrows. It applies only when AST has the value 1.
	      Its behavior also depends on the setting of the
	      parameter CTV. Assuming that CTV is set to a non-
	      zero value, implying that multi-colored vectors are
	      desired, ACM has the following settings:


	      Value   Effect
	      -----   ------
	      -2      Multi-colored fill; outline off
	      -1      Fill off; multi-colored outline
	      0	      Multi-colored fill; mono-colored outline
	      1	      Mono-colored fill; multi-colored outline
	      2	      Multi-colored fill; multi-colored outline

	      Mono-colored outlines use the current GKS polyline
	      color index. Mono-colored fill uses the current GKS
	      fill color index. When CTV is set to 0, both the
	      fill and the outlines become mono-colored, and
	      therefore only modes -2, -1, and 0 remain
	      distinguishable. The default value is 0.

       AFO - Arrow Fill Over Arrow Lines - Integer
	      If AFO is set to 1, the perimeter outline of a
	      filled vector arrow is drawn first, underneath the
	      fill. In this case, you must set the line thickness
	      parameter (LWD) to a value greater than unity in
	      order for the line to appear completely. The
	      advantage of drawing the line underneath is that
	      the full extent of the fill appears, resulting in a
	      crisper, more sharply defined arrow; when the line
	      is drawn on top of the fill using a different color
	      index, the fill color may be partially or
	      completely obscured, especially for small vector
	      arrows. AFO has an effect only when the parameter
	      AST is set to 1.	The default value of AFO is 1.

       AIR - Arrow Interior Reference Fraction	- Real
	      AIR specifies the distance from the point of the
	      arrowhead of a filled vector arrow drawn at the



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      reference length to the point where the arrowhead
	      joins with the line extending to the tail of the
	      arrow. Its value represents a fraction of the
	      reference length.	 This distance is adjusted
	      proportionally to the X component of the arrowhead
	      size for vector arrows whose length differs from
	      the reference length.  See VRL for an explanation
	      of how the reference length is determined.  AIR has
	      an effect only when AST is set to 1. AIR is allowed
	      to vary between 0.0 and 1.0 and its default value
	      is 0.33.

       AMN - Arrow Head Minimum Size - Real
	      Specifies a minimum length for the two lines
	      representing the point of the vector arrow head, as
	      a fraction of the viewport width. AMN has an effect
	      only for line-drawn vector arrows (parameter AST
	      set to 0). Normally the arrow head size is scaled
	      proportionally to the length of the vector. This
	      parameter allows you to ensure that the arrow head
	      will remain recognizable even for very short
	      vectors. Note that you can cause all the arrowheads
	      in the plot to be drawn at the same size if you set
	      AMN and AMX to the same value. If you set both AMN
	      and AMX to 0.0 the arrowheads will not be drawn at
	      all.  The default value is 0.005.

       AMX - Arrow Head Maximum Size - Real
	      Specifies a maximum length for the two lines
	      representing the point of the vector arrow head, as
	      a fraction of the viewport width.	 AMX has an
	      effect only for line-drawn vector arrows (parameter
	      AST set to 0). Normally the arrow head is scaled
	      proportionally to the length of the vector. This
	      parameter allows you to ensure that the arrow heads
	      do not become excessively large for high magnitude
	      vectors. Note that you can cause all the arrowheads
	      in the plot to be drawn at the same size if you set
	      AMN and AMX to the same value. If you set both AMN
	      and AMX to 0.0 the arrowheads will not be drawn at
	      all. The default value is 0.05.

       AST - Arrow Style - Integer

	      If AST is set to 0, the vector arrows are drawn
	      using lines only. When AST is set to 1, the vectors
	      are plotted using variable width filled arrows,
	      with an optional outline. If AST is set to 2, wind
	      barb glyphs are used to represent the vectors.There
	      are parameters for controlling the appearance of
	      each style. These have an effect only for one value
	      of AST.  However, certain parameters apply to all
	      arrow styles. Here is a table of parameters that
	      affect the appearance of vectors and how their



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      behavior is affected by the setting of AST:

	      Parameter	  Line-Drawn Arrows   Filled Arrows   Wind Barbs
	      ---------	  -----------------   -------------   ----------
	      ACM			      x
	      AFO			      x
	      AIR			      x
	      AMN	  x
	      AMX	  x
	      AWF			      x
	      AWR			      x
	      AXF			      x
	      AXR			      x
	      AYF			      x
	      AYR			      x
	      CLR	  x		      x		      x
	      CTV	  x		      x		      x
	      LWD	  x		      x		      x
	      NLV	  x		      x		      x
	      PAI	  x		      x		      x
	      TVL	  x		      x		      x
	      WBA					      x
	      WBC					      x
	      WBD					      x
	      WBS					      x
	      WBT					      x

	      When filled arrows are used, colors associated with
	      the threshold levels may be applied to either or
	      both the fill or the outline of the arrow.  When
	      fill is drawn over the outline (AFO set to 1), LWD
	      should be set to a value greater than 1.0 in order
	      for the outline to be fully visible.  The default
	      value of AST is 0.

       AWF - Arrow Width Fractional Minimum - Real
	      AWF specifies the width of a filled arrow drawn at
	      the minimum length, as a fraction of the width of
	      an arrow drawn at the reference length. If AWF has
	      the value 0.0, then the ratio of the arrow width to
	      the arrow length will be constant for all arrows in
	      the plot.	 If given the value 1.0, the width will
	      itself be constant for all arrows in the plot,
	      regardless of length. See VFR for a discussion of
	      how the minimum length is determined. AWF has an
	      effect only when AST is set to 1.	 AWF is allowed
	      to vary between 0.0 and 1.0 and its default value
	      is 0.0.

       AWR - Arrow Width Reference Fraction - Real
	      AWR specifies the width of a filled vector arrow
	      drawn at the reference length, as a fraction of the
	      reference length.	 See VRL for an explanation of
	      how the reference length is determined.  AWR has an



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      effect only when AST is set to 1. AWR is allowed to
	      vary between 0.0 and 1.0 and its default value is
	      0.03.

       AXF - Arrow X-Coord Fractional Minimum - Real
	      AXF specifies the X component of the head of a
	      filled vector arrow drawn at the minimum length, as
	      a fraction of the X component of the head of an
	      arrow drawn at the reference length. The X
	      component of the arrowhead is the distance from the
	      point of the arrowhead to a point along the
	      centerline of the arrow perpendicular the
	      arrowhead's rear tips. If AXF has the value 0.0,
	      then the ratio of the X component of the arrowhead
	      size to the arrow length will be constant for all
	      vectors in the plot. If given the value 1.0, the
	      arrowhead X component will itself be constant for
	      all arrows in the plot, regardless of their length.
	      See VRL for an explanation of how the reference
	      length is determined.  AXF has an effect only when
	      AST is set to 1. AXF is allowed to vary between 0.0
	      and 1.0 and its default value is 0.0.

       AXR - Arrow X-Coord Reference Fraction - Real
	      AXR specifies the X component of the head of a
	      filled vector arrow drawn at the reference length,
	      as a fraction of reference length. The X component
	      of the arrowhead is the distance from the point of
	      the arrowhead to a point along the centerline of
	      the arrow perpendicular the arrowhead's rear tips.
	      See VRL for an explanation of how the reference
	      length is determined.  AXR has an effect only when
	      AST is set to 1. AXR is allowed to vary between 0.0
	      and 2.0 and its default value is 0.36.

       AYF - Arrow Y-Coord Fractional Minimum - Real
	      The value of this parameter, when added to the
	      minimum width value, specifies the Y component
	      length of the arrowhead size for a filled arrow
	      drawn at the minimum length, as a fraction of the
	      length specified by AYF. If given the value 1.0,
	      the arrowhead Y component will extend the same
	      distance perpendicularly from the edge of all
	      arrows in the plot, regardless of their length and
	      width. This can be a useful resource to adjust to
	      ensure that the points of even very short vector
	      arrows remain visible. See VFR for a discussion of
	      how the minimum length is determined.  AYF has an
	      effect only when AST is set to 1. AYF is allowed to
	      vary between 0.0 and 1.0 and its default value is
	      0.25.

       AYR - Arrow Y-Coord Reference Fraction - Real
	      AYR specifies the perpendicular distance from one



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      side of a filled vector arrowdrawn at the reference
	      length to one of the back tips of the arrowhead.
	      The value represents a fraction of the value of of
	      the reference length and, when added to half the
	      arrow width, determines the Y component of the
	      arrowhead size.  See VRL for an explanation of how
	      the reference length is determined.  AYR has an
	      effect only when AST is set to 1.	 AYR is allowed
	      to vary between 0.0 and 1.0 and its default value
	      is 0.12.

       CLR - Array of GKS Color Indices - Integer Array
	      This parameter represents an array containing the
	      GKS color index to use for coloring the vector when
	      the scalar quantity is less than or equal to the
	      threshold value with the same index in the TVL
	      threshold value array. Depending on the settings of
	      AST and ACM it may specify a set of fill color
	      indexes, a set of line color indexes, or both. In
	      order to access a particular element of the CLR
	      array, you must first set the value of PAI, the
	      parameter array index parameter, to the value of
	      the array element's index. All elements of the
	      array are set to one initially. Note that the
	      Vectors utility makes no calls to set the GKS color
	      representation (GSCR), nor ever modifies the
	      contents of the CLR array; therefore you are
	      responsible for creating a suitably graduated color
	      palette and assigning the color index values into
	      the CLR array, prior to calling VVECTR. Typically,
	      assuming the desired RGB values have been
	      previously stored in a 2 dimensional 3 x n array
	      called RGB, you loop through the calls that set up
	      the color representation and color index as in the
	      following example for a fourteen color palette:

		   DO 100 I=1,14,1
		       CALL GSCR (1,I,RGB(1,I),RGB(2,I),RGB(3,I))
		       CALL VVSETI('PAI -- Parameter Array Index', I)
		       CALL VVSETI('CLR -- GKS Color Index', I)
	       100 CONTINUE

	      See the descriptions of CTV, NLV, and TVL for
	      details on configuring the vector coloring scheme.

       CPM - Compatibility Mode - Integer
	      Controls the degree of compatibility between pre-
	      Version 3.2 capabilities of the Vectors utility and
	      later versions. You can independently control three
	      behaviors using the nine settings provided:

	      +o	     use of VELVCT and VELVEC input parameters

	      +o	     use of variables initialized in the VELDAT



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


		     block data statement

	      +o	     use of the old mapping routines, FX, FY,
		     MXF, and MYF.

	      Note, however, that when using the Version 3.2
	      entry points VVINIT and VVECTR, only the third
	      behavior option has any meaning.

	      When CPM is set to 0, its default value, the
	      Vectors utility's behavior varies depending on
	      whether you access it through one of the pre-
	      Version 3.2 entry points (VELVCT, VELVEC, and
	      EZVEC), or through the VVINIT/VVECTR interface.
	      Otherwise, positive values result in invocation of
	      the pre-Version 3.2 mapping routines (FX, FY, MXF,
	      and MYF) for the conversion from data to user
	      coordinates. Negative values cause VVMPXY or
	      perhaps VVUMXY to be used instead. When using the
	      pre-Version 3.2 interface, odd values of CPM cause
	      the data values in the VELDAT block data subroutine
	      to override corresponding values initialized in the
	      Version 3.2 VVDATA block data subroutine, or set by
	      the user calling VVSETx routines. Values of CPM
	      with absolute value greater than two cause some of
	      the input arguments to VELVEC and VELVCT to be
	      ignored. These include FLO, HI, NSET, ISPV, SPV and
	      (for VELVCT only) LENGTH.

	      Here is a table of the nine settings of CPM and
	      their effect on the operation of the Vectors
	      utility:

	      Value   Use FX, FY, etc.		Use VELDAT data	  Use input args
	      -----   ----------------		---------------	  --------------
	      -4      no			no		  no
	      -3      no			yes		  no
	      -2      no			no		  yes
	      -1      no			yes		  yes
	      0	      old - yes; new - no (*)	yes		  yes
	      1	      yes			yes		  yes
	      2	      yes			no		  yes
	      3	      yes			yes		  no
	      4	      yes			no		  no

	      (*) Old means EZVEC, VELVEC, VELVCT entry point;
	      new, VVINIT/VVECTR.  Only the first column applies
	      to the VVINIT/VVECTR interface. See the velvct man
	      page for more detailed emulation information.

       CTV - Color Threshold Value Control - Integer
	      In conjunction with NLV, this parameter controls
	      vector coloring and the setting of threshold
	      values. The vectors may be colored based on on the



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      vector magnitude or on the contents of a scalar
	      array (VVINIT/VVECTR input argument, P). A table of
	      supported options follows:

	      Value	     Action

	      -2	     Color vector arrows based on scalar
			     array data values; the user is
			     responsible for setting up threshold
			     level array, TVL

	      -1	     Color vector arrows based on vector
			     magnitude; the user is responsible
			     for setting up values of threshold
			     level array.

	      0(default)     Color all vectors according to the
			     current GKS polyline color index
			     value. Threshold level array, TVL
			     and GKS color index array, CLR are
			     not used.

	      1		     Color vector arrows based on vector
			     magnitude; VVINIT assigns values to
			     the first NLV elements of the
			     threshold level array, TVL.

	      2		     Color vector arrows based on scalar
			     array data values; VVINIT assigns
			     values to the first NLV elements of
			     the threshold level array, TVL.

	      If you make CTV positive, you must initialize
	      Vectors with a call to VVINIT after the
	      modification.

       DMN - NDC Minimum Vector Size - Real, Read-Only
	      This parameter is read-only and has a useful value
	      only following a call to VVECTR (directly or
	      through the compatibility version of VELVCT). You
	      may retrieve it in order to determine the length in
	      NDC space of the smallest vector actually drawn (in
	      other words, the smallest vector within the
	      boundary of the user coordinate space that is
	      greater than or equal in magnitude to the value of
	      the VLC parameter). It is initially set to a value
	      of 0.0.

       DMX - NDC Maximum Vector Size - Real, Read-Only
	      Unlike DMN this read-only parameter has a
	      potentially useful value betweens calls to VVINIT
	      and VVECTR. However, the value it reports may be
	      different before and after the call to VVECTR.
	      Before the VVECTR call it contains the length in



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      NDC space that would be used to render the maximum
	      size vector assuming the user-settable parameter,
	      VRL is set to its default value of 0.0.  After the
	      VVECTR call it contains the NDC length used to
	      render the largest vector actually drawn (in other
	      words, the largest vector within the boundary of
	      the user coordinate space that is less than or
	      equal in magnitude to the value of the VHC
	      parameter). See the section on the VRL parameter
	      for information on using the value of DMX after the
	      VVINIT call in order to adjust proportionally the
	      lengths of all the vectors in the plot.  It is
	      initially set to a value of 0.0.

       DPF - Vector Label Decimal Point Control Flag - Integer
	      If DPF is set to a non-zero value, and the optional
	      vector magnitude labels are enabled, the magnitude
	      values are scaled to fit in the range 1 to 999. The
	      labels will contain 1 to 3 digits and no decimal
	      point. Otherwise, the labels will consist of a
	      number up to six characters long, including a
	      decimal point. By default DPF is set to the value
	      1.

       LBC - Vector Label Color - Integer
	      This parameter specifies the color to use for the
	      optional vector magnitude labels, as follows:

	      Value	     Action

	      < -1	     Draw labels using the current GKS
			     text color index

	      -1 (default)   Draw labels using the same color as
			     the corresponding vector arrow

	      >=0	     Draw labels using the LBC value as
			     the GKS text color index

       LBL - Vector Label Flag - Integer
	      If set non-zero, Vectors draws labels representing
	      the vector magnitude next to each arrow in the
	      field plot.  The vector labels are primarily
	      intended as a debugging aid, since in order to
	      avoid excessive overlap, you must typically set the
	      label text size too small to be readable without
	      magnification. For this reason, as well as for
	      efficiency, unlike the other graphical text
	      elements supported by the Vectors utility, the
	      vector labels are rendered using low quality text.

       LBS - Vector Label Character Size - Real
	      This parameter specifies the size of the characters
	      used for the vector magnitude labels as a fraction



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      of the viewport width. The default value is 0.007.

       LWD - Vector Linewidth - Real

	      LWD controls the linewidth used to draw the lines
	      that form vector arrows and wind barbs. When the
	      arrows are filled (AST is set to 1) LWD controls
	      the width of the arrow's outline. If the fill is
	      drawn over the outline (AFO set to 1) then LWD must
	      be set to a value greater than 1.0 in order for the
	      outline to appear properly. When AST has the value
	      2, LWD controls the width of the line elements of
	      wind barbs. When AST is set to 0, specifying line-
	      drawn vector arrows, the linewidth applies equally
	      to the body of the vector and the arrowhead. Overly
	      thick lines may cause the arrow heads to appear
	      smudged. This was part of the motivation for
	      developing the option of filled vector arrows. Note
	      that since linewidth in NCAR Graphics is always
	      calculated relative to a unit linewidth that is
	      dependent on the output device, you may need to
	      adjust the linewidth value depending on the
	      intended output device to obtain a pleasing plot.
	      The default is 1.0, specifying a device-dependent
	      minimum linewidth.


       MAP - Map Transformation Code - Integer
	      MAP defines the transformation between the data and
	      user coordinate space.  Three MAP parameter codes
	      are reserved for pre-defined transformations, as
	      follows:

	      Value	     Mapping transformation

	      0 (default)    Identity transformation between data
			     and user coordinates: array indices
			     of U, V, and P are linearly related
			     to data coordinates.

	      1		     Ezmap transformation: first
			     dimension indices of U, V, and P are
			     linearly related to longitude;
			     second dimension indices are
			     linearly related to latitude.

	      2		     Polar to rectangular transformation:
			     first dimension indices of U, V, and
			     P are linearly related to the
			     radius; second dimension indices are
			     linearly related to the angle in
			     degrees.

	      If MAP has any other value, Vectors invokes the



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      user-modifiable subroutine, VVUMXY, to perform the
	      mapping.	The default version of VVUMXY simply
	      performs an identity transformation. Note that,
	      while the Vectors utility does not actually
	      prohibit the practice, the user is advised not to
	      use negative integers for user-defined mappings,
	      since other utilities in the NCAR Graphics toolkit
	      attach a special meaning to negative mapping codes.

	      For all the predefined mappings, the linear
	      relationship between the grid array indices and the
	      data coordinate system is established using the
	      four parameters, XC1, XCM, YC1, and YCN. The X
	      parameters define a mapping for the first and last
	      indices of the first dimension of the data arrays,
	      and the Y parameters do the same for the second
	      dimension. If MAP is set to a value of one, be
	      careful to ensure that the SET parameter is given a
	      value of zero, since the Ezmap routines require a
	      specific user coordinate space for each projection
	      type, and internally call the SET routine to define
	      the user to NDC mapping.	Otherwise, you may choose
	      whether or not to issue a SET call prior to calling
	      VVINIT, modifying the value of SET as required.
	      See the description of the parameter, TRT, and the
	      vvumxy man page for more information.

       MNC - Minimum Vector Text Block Color - Integer
	      MNC specifies the color of the minimum vector
	      graphical text output block as follows:

	      Value	     Action

	      <-2	     Both the vector arrow and the text
			     are colored using the current text
			     color index.

	      -2	     If the vectors are colored by
			     magnitude, both the vector arrow and
			     the text use the GKS color index
			     associated with the minimum vector
			     magnitude. Otherwise, the vector
			     arrow uses the current polyline
			     color index and the text uses the
			     current text color index.

	      -1 (default)   If the vectors are colored by
			     magnitude, the vector arrow uses the
			     GKS color index associated with the
			     minimum vector magnitude. Otherwise
			     the vector arrow uses the current
			     polyline color index. The text is
			     colored using the current text color
			     index in either case.



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      >= 0	     The value of MNC is used as the
			     color index for both the text and
			     the vector arrow

	      See the description of MNT for more information
	      about the minimum vector text block.

       MNP - Minimum Vector Text Block Positioning Mode - Integer
	      This parameter allows you to justify the minimum
	      vector text block, taken as a single unit, relative
	      to the text block position established by the
	      parameters, MNX and MNY. Nine positioning modes are
	      available, as follows:

	      Mode	     Justification

	      -4	     The lower left corner of the text
			     block is positioned at MNX, MNY.

	      -3	     The center of the bottom edge is
			     positioned at MNX, MNY.

	      -2	     The lower right corner is positioned
			     at MNX, MNY.

	      -1	     The center of the left edge is
			     positioned at MNX, MNY.

	      0		     The text block is centered along
			     both axes at MNX, MNY.

	      1		     The center of the right edge is
			     positioned at MNX, MNY.

	      2		     The top left corner is positioned at
			     MNX, MNY.

	      3		     The center of the top edge is
			     positioned at MNX, MNY.

	      4 (default)    The top right corner is positioned
			     at MNX, MNY.

	      See the description of MNT for more information
	      about the minimum vector text block.

       MNS - Minimum Vector Text Block Character Size - Real
	      MNS specifies the size of the characters used in
	      the minimum vector graphics text block as a
	      fraction of the viewport width. See the description
	      of MNT for more information about the minimum
	      vector text block. The default value of MNS is
	      0.0075.




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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


       MNT - Minimum Vector Text String - Character* 36
	      The minimum vector graphics text block consists of
	      a user-definable text string centered underneath a
	      horizontal arrow. If the parameter VLC is set
	      negative the arrow is rendered at the size of the
	      reference minimum magnitude vector (which may be
	      smaller than any vector that actually appears in
	      the plot). Otherwise, the arrow is the size of the
	      smallest vector in the plot. Directly above the
	      arrow is a numeric string in exponential format
	      that represents the vector's magnitude.

	      Use MNT to modify the text appearing below the
	      vector in the minimum vector graphics text block.
	      Currently the string length is limited to 36
	      characters. Set MNT to a single space (' ') to
	      remove the text block, including the vector arrow
	      and the numeric magnitude string, from the plot.
	      The default value is 'Minimum Vector'

       MNX - Minimum Vector Text Block X Coordinate - Real
	      MNX establishes the X coordinate of the minimum
	      vector graphics text block as a fraction of the
	      viewport width.  Values less than 0.0 or greater
	      than 1.0 are permissible and respectively represent
	      regions to the left or right of the viewport. The
	      actual position of the block relative to MNX
	      depends on the value assigned to MNP. See the
	      descriptions of MNT and MNP for more information
	      about the minimum vector text block. The default
	      value of MNX is 0.475.

       MNY - Minimum Vector Text Block Y Coordinate - Real
	      MNY establishes the Y coordinate of the minimum
	      vector graphics text block as a fraction of the
	      viewport height.	Values less than 0.0 or greater
	      than 1.0 are permissible and respectively represent
	      regions below or above the viewport. The actual
	      position of the block relative to MNY depends on
	      the value assigned to MNP. See the descriptions of
	      MNT and MNP for more information about the minimum
	      vector text block. The default value of MNY is
	      -0.01.

       MSK - Mask To Area Map Flag - Integer
	      Use this parameter to control masking of vectors to
	      an existing area map created by routines in the
	      Areas utility.  When MSK is greater than 0, masking
	      is enabled and an the area map must be set up prior
	      to the call to VVECTR. The area map array and, in
	      addition, the name of a user-definable masked
	      drawing routine, must be passed as input parameters
	      to VVECTR. Various values of the MSK parameter have
	      the following effects:



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      Value	     Effect

	      <= 0 (default) No masking of vectors.

	      1		     The subroutine ARDRLN is called
			     internally to decompose the vectors
			     into segments contained entirely
			     within a single area.  ARDRLN calls
			     the user-definable masked drawing
			     subroutine.

	      >1	     Low precision masking. ARGTAI is
			     called internally to get the area
			     identifiers for the vector base
			     position point. Then the user-
			     definable masked drawing subroutine
			     is called to draw the vector.
			     Vectors with nearby base points may
			     encroach into the intended mask
			     area.

	      See the man page vvudmv for further explanation of
	      masked drawing of vectors

       MXC - Maximum Vector Text Block Color - Integer
	      MXC specifies the color of the maximum vector
	      graphical text output block as follows:

	      Value	     Action

	      <-2	     Both the vector arrow and the text
			     are colored using the current text
			     color index.

	      -2	     If the vectors are colored by
			     magnitude, both the vector arrow and
			     the text use the GKS color index
			     associated with the minimum vector
			     magnitude. Otherwise, the vector
			     arrow uses the current polyline
			     color index and the text uses the
			     current text color index.

	      -1 (default)   If the vectors are colored by
			     magnitude, the vector arrow uses the
			     GKS color index associated with the
			     minimum vector magnitude. Otherwise
			     the vector arrow uses the current
			     polyline color index. The text is
			     colored using the current text color
			     index in either case.

	      >= 0	     The value of MXC is used as the
			     color index for both the text and



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


			     the vector arrow

	      See the description of MXT for more information
	      about the maximum vector text block.

       MXP - Maximum Vector Text Block Positioning Mode - Integer
	      This parameter allows you to justify the maximum
	      vector text block, taken as a single unit, relative
	      to the text block position established by the
	      parameters, MXX and MXY. Nine positioning modes are
	      available, as follows:

	      Mode	     Justification

	      -4	     The lower left corner of the text
			     block is positioned at MXX, MXY.

	      -3	     The center of the bottom edge is
			     positioned at MXX, MXY.

	      -2	     The lower right corner is positioned
			     at MXX, MXY.

	      -1	     The center of the left edge is
			     positioned at MXX, MXY.

	      0		     The text block is centered along
			     both axes at MXX, MXY.

	      1		     The center of the right edge is
			     positioned at MXX, MXY.

	      2		     The top left corner is positioned at
			     MXX, MXY.

	      3		     The center of the top edge is
			     positioned at MXX, MXY.

	      4		     The top right corner is positioned
			     at MXX, MXY.

	      See the description of MXT for more information
	      about the maximum vector text block.

       MXS - Maximum Vector Text Block Character Size - Real
	      MXS specifies the size of the characters used in
	      the maximum vector graphics text block as a
	      fraction of the viewport width. See the description
	      of MXT for more information about the maximum
	      vector text block. The default value is 0.0075.

       MXT - Maximum Vector Text String - Character* 36
	      The maximum vector graphics text block consists of
	      a user-definable text string centered underneath a



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      horizontal arrow. If the parameter VHC is set
	      negative the arrow is rendered at the size of the
	      reference maximum magnitude vector (which may be
	      larger than any vector that actually appears in the
	      plot). Otherwise, the arrow is the size of the
	      largest vector in the plot. Directly above the
	      arrow is a numeric string in exponential format
	      that represents the magnitude of this vector.

	      Use MXT to modify the text appearing below the
	      vector in the maximum vector graphics text block.
	      Currently the string length is limited to 36
	      characters. Set MXT to a single space (' ') to
	      completely remove the text block, including the
	      vector arrow and the numeric magnitude string, from
	      the plot. Note that the name "Maximum Vector Text
	      Block" is no longer accurate, since using the
	      parameter VRM it is now possible to establish a
	      reference magnitude that is smaller than the
	      maximum magnitude in the data set. A more accurate
	      name would be "Reference Vector Text Block".  The
	      default value of MXT is 'Maximum Vector'.

       MXX - Maximum Vector Text Block X Coordinate - Real
	      MXX establishes the X coordinate of the maximum
	      vector graphics text block as a fraction of the
	      viewport width.  Values less than 0.0 or greater
	      than 1.0 are permissible and respectively represent
	      regions below or above of the viewport. The actual
	      position of the block relative to MXX depends on
	      the value assigned to MXP. See the descriptions of
	      MXT and MXP for more information about the maximum
	      vector text block. The default value is 0.525.

       MXY - Maximum Vector Text Block Y Coordinate - Real
	      MXY establishes the Y coordinate of the maximum
	      vector graphics text block as a fraction of the
	      viewport width.  Values less than 0.0 or greater
	      than 1.0 are permissible and respectively represent
	      regions below or above the viewport. The actual
	      position of the block relative to MXY depends on
	      the value assigned to MXP. See the descriptions of
	      MXT and MXP for more information about the maximum
	      vector text block.  The default value is -0.01.

       NLV - Number of Colors Levels - Integer
	      NLV specifies the number of color levels to use
	      when coloring the vectors according to data in a
	      scalar array or by vector magnitude.  Anytime CTV
	      has a non-zero value, you must set up the first NLV
	      elements of the color index array CLR. Give each
	      element the value of a GKS color index that must be
	      defined by a call to the the GKS subroutine, GSCR,
	      prior to calling VVECTR. If CTV is less than 0, in



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      addition to setting up the CLR array, you are also
	      responsible for setting the first NLV elements of
	      the threshold values array, TVL to appropriate
	      values. NLV is constrained to a maximum value of
	      255. The default value of NLV is 0, specifying that
	      vectors are colored according to the value of the
	      GKS polyline color index currently in effect,
	      regardless of the value of CTV.  If CTV is greater
	      than 0, you must initialize Vectors with a call to
	      VVINIT after modifying this parameter.

       PAI - Parameter Array Index - Integer
	      The value of PAI must be set before calling VVGETC,
	      VVGETI, VVGETR, VVSETC, VVSETI, or VVSETR to access
	      any parameter which is an array; it acts as a
	      subscript to identify the intended array element.
	      For example, to set the 10th color threshold array
	      element to 7, use code like this:

	       CALL VVSETI ('PAI - PARAMETER ARRAY INDEX',10)
	       CALL VVSETI ('CLR - Color Index',7)

	      The default value of PAI is one.

       PLR - Polar Input Mode - Integer
	      When PLR is greater than zero, the vector component
	      arrays are considered to contain the field data in
	      polar coordinate form: the U array is treated as
	      containing the vector magnitude and the V array as
	      containing the vector angle. Be careful not to
	      confuse the PLR parameter with the MAP parameter
	      set to polar coordinate mode (2). The MAP parameter
	      relates to the location of the vector, not its
	      value. Here is a table of values for PLR:

	      Value	     Meaning

	      0 (default)    U and V arrays contain data in
			     cartesian component form.

	      1		     U array contains vector magnitudes;
			     V array contains vector angles in
			     degrees.

	      2		     U array contain vector magnitudes; V
			     array contains vector angles in
			     radians.

	      You must initialize Vectors with a call to VVINIT
	      after modifying this parameter.

       PMN - Minimum Scalar Array Value - Real, Read-Only
	      You may retrieve the value specified by PMN at any
	      time after a call to VVINIT. It will contain a copy



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      of the minimum value encountered in the scalar data
	      array. If no scalar data array has been passed into
	      VVINIT it will have a value of 0.0.

       PMX - Maximum Scalar Array Value - Real
	      You may retrieve the value specified by PMX at any
	      time after a call to VVINIT. It contains a copy of
	      the maximum value encountered in the scalar data
	      array.  If no scalar data array has been passed
	      into VVINIT it will have a value of 0.0.

       PSV - P Array Special Value - Real
	      Use PSV to indicate the special value that flags an
	      unknown data value in the P scalar data array. This
	      value will not be considered in the determination
	      of the data set maximum and minimum values. Also,
	      depending on the setting of the SPC parameter, the
	      vector may be specially colored to flag the unknown
	      data point, or even eliminated from the plot. You
	      must initialize Vectors with a call to VVINIT after
	      modifying this parameter.

       SET - SET Call Flag - Integer
	      Give SET the value 0 to inhibit the SET call VVINIT
	      performs by default. Arguments 5-8 of a SET call
	      made by the user must be consistent with the ranges
	      of the user coordinates expected by Vectors. This
	      is determined by the mapping from grid to data
	      coordinates as specified by the values of the
	      parameters XC1, XCM, YC1, YCN, and also by the
	      mapping from data to user coordinates established
	      by the MAP parameter. You must initialize Vectors
	      with a call to VVINIT after modifying this
	      parameter. The default value of SET is 1.

       SPC - Special Color - Integer
	      SPC controls special value processing for the
	      optional scalar data array used to color the
	      vectors, as follows:

	      Value	     Effect

	      < 0 (default)  The P scalar data array is not
			     examined for special values.

	      0		     Vectors at P scalar array special
			     value locations are not drawn.

	      > 0	     Vectors at P scalar array special
			     value locations are drawn using
			     color index SPC.

	      You must initialize Vectors with a call to VVINIT
	      after modifying this parameter.



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


       SVF - Special Value Flag - Integer
	      The special value flag controls special value
	      processing for the U and V vector component data
	      arrays. Special values may appear in either the U
	      or V array or in both of them. Five different
	      options are available (although the usefulness of
	      some of the choices is debatable):

	      Value	     Effect

	      0 (default)    Neither the U nor the V array is
			     examined for special values

	      1		     Vectors with special values in the U
			     array are not drawn

	      2		     Vectors with special values in the V
			     array are not drawn

	      3		     Vectors with special values in
			     either the U or V array are not
			     drawn

	      4		     Vectors with special values in both
			     the U and V arrays are not drawn

	      The U and V special values are defined by setting
	      parameters USV and VSV. You must initialize Vectors
	      with a call to VVINIT after modifying this
	      parameter.

       TRT - Transformation Type - Integer
	      As currently implemented, TRT further qualifies the
	      mapping transformation specified by the MAP
	      parameter, as follows:

	      Value	     Effect

	      -1	     Direction, magnitude, and location
			     are all transformed. This option is
			     not currently supported by any of
			     the pre-defined coordinate system
			     mappings.

	      0		     Only location is transformed

	      1 (default)    Direction and location are
			     transformed

	      This parameter allows you to distinguish between a
	      system that provides a mapping of location only
	      into an essentially cartesian space, and one in
	      which the space itself mapped. To understand the
	      difference, using polar coordinates as an example,



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      imagine a set of wind speed monitoring units
	      located on a radial grid around some central point
	      such as an airport control tower. Each unit's
	      position is defined in terms of its distance from
	      the tower and its angular direction from due east.
	      However, the data collected by each monitoring unit
	      is represented as conventional eastward and
	      northward wind components.  Assuming the towers's
	      location is at a moderate latitude, and the
	      monitoring units are reasonably 'local', this is an
	      example of mapping a radially defined location into
	      a nearly cartesian space (i.e. the eastward
	      components taken alone all point in a single
	      direction on the plot, outlining a series of
	      parallel straight lines). One would set MAP to two
	      (for the polar transformation) and TRT to zero to
	      model this data on a plot generated by the Vectors
	      utility.

	      On the other hand, picture a set of wind data,
	      again given as eastward and northward wind
	      components, but this time the center of the polar
	      map is actually the south pole. In this case, the
	      eastward components do not point in a single
	      direction; instead they outline a series of circles
	      around the pole. This is a space mapping
	      transformation: one would again set MAP to two, but
	      TRT would be set to one to transform both direction
	      and location.

	      Changing the setting of this parameter affects the
	      end results only when a non-uniform non-linear
	      mapping occurs at some point in the transformation
	      pipeline. For this discussion a uniform linear
	      transformation is defined as one which satisfies
	      the following equations:

	       x_out = x_offset + scale_constant * x_in
	       y_out = y_offset + scale_constant * y_in

	      If scale_constant is not the same for both the X
	      axis and the Y axis then the mapping is non-
	      uniform.

	      This option is currently implemented only for the
	      pre-defined MAP parameter codes, 0 and 2, the
	      identity mapping and the polar coordinate mapping.
	      However, it operates on a different stage of the
	      transformation pipeline in each case. The polar
	      mapping is non-linear from data to user
	      coordinates. The identity mapping, even though
	      necessarily linear over the data to user space
	      mapping, can have a non-uniform mapping from user
	      to NDC space, depending on the values given to the



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      input parameters of the SET call. This will be the
	      case whenever the LL input parameter is other than
	      one, or when LL equals one, but the viewport and
	      the user coordinate boundaries do not have the same
	      aspect ratio. Thus for a MAP value of 2, TRT
	      affects the mapping between data and user space,
	      whereas for MAP set to 0, TRT influences the
	      mapping between user and NDC space.

       TVL - Array of Threshold Values - Real Array
	      TVL is an array of threshold values that is used to
	      determine the individual vector color, when CTV and
	      NLV are both non-zero. For each vector the TVL
	      array is searched for the smallest value greater
	      than or equal to the scalar value associated with
	      the vector. The array subscript of this element is
	      used as an index into the CLR array.  Vectors uses
	      the GKS color index found at this element of the
	      CLR array to set the color for the vector. Note
	      that Vectors assumes that the threshold values are
	      monotonically increasing.

	      When CTV is less than 0, you are responsible for
	      assigning values to the elements of TVL yourself.
	      To do this, first set the PAI parameter to the
	      index of the threshold level element you want to
	      define, then call VVSETR to set TVL to the
	      appropriate threshold value for this element.
	      Assuming the desired values have previously been
	      stored in a array named TVALS, you could assign the
	      threshold values for a fourteen level color palette
	      using the following loop:

		   DO 100 I=1,14,1
		       CALL VVSETI(PAI -- Parameter Array Index, I)
		       CALL VVSETR(TVL -- Threshold Value, TVALS(I))
	       100 CONTINUE

	      When CTV is greater than 0, Vectors assigns values
	      into TVL itself. Each succeeding element value is
	      greater than the preceding value by the value of
	      the expression:

	       (maximum_data_value - minimum_data_value) / NLV

	      where the data values are either from the scalar
	      data array or are the magnitudes of the vectors in
	      the vector component arrays. The first value is
	      equal to the minimum value plus the expression; the
	      final value (indexed by the value of NLV) is equal
	      to the maximum value. If Vectors encounters a value
	      greater than the maximum value in the TVL array
	      while processing the field data, it gives the
	      affected vector the color associated with the



UNIX			    April 1993			       20





Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      maximum TVL value.

       USV - U Array Special Value - Real
	      USV is the U vector component array special value.
	      It is a value outside the range of the normal data
	      used to indicate that there is no valid data for
	      this grid location. When SVF is set to 1 or 3,
	      Vectors will not draw a vector whose U component
	      has the special value. You must initialize Vectors
	      with a call to VVINIT after modifying this
	      parameter. It has a default value of 1.0 E12.

       VFR - Minimum Vector Fractional Length - Real
	      Use this parameter to adjust the realized size of
	      the reference minimum magnitude vector relative to
	      the reference maximum magnitude vector in order to
	      improve the appearance or perhaps the information
	      content of the plot. Specify VFR as a value between
	      0.0 and 1.0, where 0.0 represents an unmodified
	      linear scaling of the realized vector length, in
	      proportion to magnitude, and 1.0 specifies that the
	      smallest vector be represented at 1.0 times the
	      length of the largest vector, resulting in all
	      vectors, regardless of magnitude, having the same
	      length on the plot. A value of 0.5 means that the
	      smallest magnitude vector appears half as long as
	      the largest magnitude vector; intermediate sizes
	      are proportionally scaled to lengths between these
	      extremes. Where there is a wide variation in
	      magnitude within the vector field, you can use this
	      parameter to increase the size of the smallest
	      vectors to a usefully visible level. Where the
	      variation is small, you can use the parameter to
	      exaggerate the differences that do exist. See also
	      the descriptions of VRL, VLC, VHC, and VRM. The
	      default value is 0.0.

       VHC - Vector High Cutoff Value - Real
	      If the parameter VRM is set to a value greater than
	      0.0, it supercedes the use of VHC to specify the
	      reference magnitude. VRM allows greater flexibility
	      in that it can be used to specify an arbitrary
	      reference magnitude that need not be the maximum
	      magnitude contained in the data set. VHC can still
	      be used to set a high cutoff value -- no vectors
	      with magnitude greater than the cutoff value will
	      be displayed in the plot.

	      If VRM has its default value, 0.0, VHC specifies
	      the reference maximum magnitude represented by an
	      arrow of length VRL (as a fraction of the viewport
	      width). The realized length of each individual
	      vector in the plot is based on its magnitude
	      relative to the reference maximum magnitude and, if



UNIX			    April 1993			       21





Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      VFR is non-zero, the reference minimum magnitude
	      (as specified by VLC). Note that the reference
	      maximum magnitude may be greater than the magnitude
	      of any vector in the dataset. The effect of this
	      parameter varies depending on its value, as
	      follows:

	      Value	     Effect

	      < 0.0	     The absolute value of VHC
			     unconditionally determines the
			     reference maximum magnitude. Vectors
			     in the dataset with magnitude
			     greater than VHC are not displayed.

	      0.0 (default)  The vector with the greatest
			     magnitude in the dataset determines
			     the reference maximum magnitude.

	      > 0.0	     The minimum of VHC and the vector
			     with the greatest magnitude in the
			     data set determines the reference
			     maximum magnitude. Vectors in the
			     dataset with magnitude greater than
			     VHC are not displayed.

	      Typically, for direct comparison of the output of a
	      series of plots, you would set VHC to a negative
	      number, the absolute value of which is greater than
	      any expected vector magnitude in the series. You
	      can turn on Vectors statistics reporting using the
	      parameter VST in order to see if any vectors in the
	      datasets do exceed the maximum magnitude you have
	      specified. See also the descriptions of the
	      parameters VRM, VRL, DMX, VLC, and VFR.

       VLC - Vector Low Cutoff Value - Real
	      Use this parameter to prevent vectors smaller than
	      the specified magnitude from appearing in the
	      output plot. VLC also specifies the reference
	      minimum magnitude that is rendered at the size
	      specified by the product of VRL and VFR (as a
	      fraction of the viewport width), when VFR is
	      greater than 0.0. Note that the reference minimum
	      magnitude may be smaller than the magnitude of any
	      vector in the dataset. The effect of this parameter
	      varies depending on its value, as follows:

	      Value	     Effect

	      < 0.0	     The absolute value of VLC
			     unconditionally determines the
			     reference minimum magnitude. Vectors
			     in the dataset with magnitude less



UNIX			    April 1993			       22





Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


			     than VLC do not appear.

	      0.0 (default)  The vector with the minimum
			     magnitude in the dataset determines
			     the reference minimum magnitude.

	      > 0.0	     The maximum of VLC and the vector
			     with the least magnitude in the data
			     set determines the reference minimum
			     magnitude. Vectors in the dataset
			     with magnitude less than VLC do not
			     appear.

	      The initialization subroutine, VVINIT, calculates
	      the magnitude of all the vectors in the vector
	      field, and stores the maximum and minimum values.
	      You may access these values by retrieving the read-
	      only parameters, VMX and VMN.  Thus it is possible
	      to remove the small vectors without prior knowledge
	      of the data domain. The following code fragment
	      illustrates how the smallest 10% of the vectors
	      could be removed:

	       CALL VVINIT(...
	       CALL VVGETR('VMX - Vector Maximum Magnitude', VMX)
	       CALL VVGETR('VMN - Vector Minimum Magnitude', VMN)
	       CALL VVSETR('VLC - Vector Low Cutoff Value',
	      +	    VMN+0.1*(VMX-VMN))
	       CALL VVECTR(...


	      On the other hand, when creating a series of plots
	      that you would like to compare directly and you are
	      using VFR to set a minimum realized size for the
	      vectors, you can ensure that all vectors of a
	      particular length represent the same magnitude on
	      all the plots by setting both VHC and VLC to
	      negative values. If you do not actually want to
	      remove any vectors from the plot, make VLC smaller
	      in absolute value than any expected magnitude. You
	      can turn on Vectors statistics reporting using the
	      parameter VST in order to see if any vectors in the
	      datasets are less the minimum magnitude you have
	      specified. See also the descriptions of parameters
	      VFR, VRL, VHC, DMN, and VRM.

       VMD - Vector Minimum Distance - Real
	      If VMD is set to a value greater than 0.0, it
	      specifies, as a fraction of the viewport width, a
	      minimum distance between adjacent vectors arrows in
	      the plot. The distribution of vectors is analyzed
	      and then vectors are selectively removed in order
	      to ensure that the remaining vectors are separated
	      by at least the specified distance. The thinning



UNIX			    April 1993			       23





Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      algorithm requires that you supply Vectors with a
	      work array twice the size of the VVINIT arguments N
	      and M multiplied together. Use of this capability
	      adds some processing time to the execution of
	      Vectors. If VMD is set to a value greater than 0.0
	      and no work array is provided, an error condition
	      results.

	      If the data grid is transformed in such a way that
	      adjacent grid cells become very close in NDC space,
	      as for instance in many map projections near the
	      poles, you can use this parameter to reduce the
	      otherwise cluttered appearance of these regions of
	      the plot. The default value of VMD is 0.0.

       VMN - Minimum Vector Magnitude - Real, Read-Only
	      After a call to VVINIT, VMN contains the value of
	      the minimum vector magnitude in the U and V vector
	      component arrays. Later, after VVECTR is called, it
	      is modified to contain the magnitude of the
	      smallest vector actually displayed in the plot.
	      This is the vector with the smallest magnitude
	      greater than or equal to the value specified by
	      VLC, the vector low cutoff parameter, (0.0 if VLC
	      has its default value) that falls within the user
	      coordinate window boundaries. The value contained
	      in VMN is the same as that reported as the 'Minimum
	      plotted vector magnitude' when Vectors statistics
	      reporting is enabled. It may be larger than the
	      reference minimum magnitude reported by the minimum
	      vector text block if you specify the VLC parameter
	      as a negative value. VMN is initially set to a
	      value of 0.0.

       VMX - Maximum Vector Magnitude - Real, Read-Only
	      After a call to VVINIT, VMX contains the value of
	      the maximum vector magnitude in the U and V vector
	      component arrays. Later, after VVECTR is called, it
	      is modified to contain the magnitude of the largest
	      vector actually displayed in the plot. This is the
	      vector with the largest magnitude less than or
	      equal to the value specified by VHC, the vector
	      high cutoff parameter, (the largest floating point
	      value available on the machine if VHC has its
	      default value, 0.0) that falls within the user
	      coordinate window boundaries. The value contained
	      in VMX is the same as that reported as the 'Maximum
	      plotted vector magnitude' when Vectors statistics
	      reporting is enabled. It may be smaller than the
	      reference maximum magnitude reported by the maximum
	      vector text block if you specify the VHC parameter
	      as a negative value. VMX is initially set to a
	      value of 0.0.




UNIX			    April 1993			       24





Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


       VPB - Viewport Bottom - Real
	      The parameter VPB has an effect only when SET is
	      non-zero, specifying that Vectors should do the
	      call to SET. It specifies a minimum boundary value
	      for the bottom edge of the viewport in NDC space,
	      and is constrained to a value between 0.0 and 1.0.
	      It must be less than the value of the Viewport Top
	      parameter, VPT. The actual value of the viewport
	      bottom edge used in the plot may be greater than
	      the value of VPB, depending on the setting of the
	      Viewport Shape parameter, VPS.  You must initialize
	      Vectors with a call to VVINIT after modifying this
	      parameter. The default value of VPB is 0.05.

       VPL - Viewport Left - Real
	      The parameter VPL has an effect only when SET is
	      non-zero, specifying that Vectors should do the
	      call to SET. It specifies a minimum boundary value
	      for the left edge of the viewport in NDC space, and
	      is constrained to a value between 0.0 and 1.0. It
	      must be less than the value of the Viewport Right
	      parameter, VPR. The actual value of the viewport
	      left edge used in the plot may be greater than the
	      value of VPL, depending on the setting of the
	      Viewport Shape parameter, VPS.  You must initialize
	      Vectors with a call to VVINIT after modifying this
	      parameter. The default value of VPL is 0.05.

       VPO - Vector Positioning Mode - Integer
	      VPO specifies the position of the vector arrow in
	      relation to the grid point location of the vector
	      component data.  Three settings are available, as
	      follows:

	      Value	     Effect

	      <0	     The head of the vector arrow is
			     placed at the grid point location

	      0 (default)    The center of the vector arrow is
			     placed at the grid point location

	      >0	     The tail of the vector arrow is
			     placed at the grid point location

       VPR - Viewport Right - Real
	      The parameter VPR has an effect only when SET is
	      non-zero, specifying that Vectors should do the
	      call to SET. It specifies a maximum boundary value
	      for the right edge of the viewport in NDC space,
	      and is constrained to a value between 0.0 and 1.0.
	      It must be greater than the value of the Viewport
	      Left parameter, VPL. The actual value of the
	      viewport right edge used in the plot may be less



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      than the value of VPR, depending on the setting of
	      the Viewport Shape parameter, VPS.  You must
	      initialize Vectors with a call to VVINIT after
	      modifying this parameter. The default value of VPR
	      is 0.95.

       VPS - Viewport Shape - Real
	      The parameter VPS has an effect only when SET is
	      non-zero, specifying that Vectors should do the
	      call to SET; it specifies the desired viewport
	      shape, as follows:

	      Value	     Effect

	      <0.0	     The absolute value of VPS specifies
			     the shape to use for the viewport.,
			     as the ratio of the viewport width
			     to its height,

	      0.0	     The viewport completely fills the
			     area defined by the boundaries
			     specifiers, VPL, VPR, VPB, VPT

	      >0.0,<1.0 (0.25, default)
			     Use R = (XCM-XC1)/(YCN-YC1) as the
			     viewport shape if MIN(R, 1.0/R) is
			     greater than VPS. Otherwise
			     determine the shape as when VPS is
			     equal to 0.0.

	      >= 1.0	     Use R = (XCM-XC1)/(YCN-YC1) as the
			     viewport shape if MAX(R, 1.0/R) is
			     less than VPS. Otherwise make the
			     viewport a square.

	      The viewport, whatever its final shape, is centered
	      in, and made as large as possible in, the area
	      specified by the parameters VPB, VPL, VPR, and VPT.
	      You must initialize Vectors with a call to VVINIT
	      after modifying this parameter. The default value
	      of VPS is 25.

       VPT - Viewport Top - Real
	      The parameter VPT has an effect only when SET is
	      non-zero, specifying that Vectors should do the
	      call to SET. It specifies a maximum boundary value
	      for the top edge of the viewport in NDC space, and
	      is constrained to a value between 0.0 and 1.0. It
	      must be greater than the value of the Viewport
	      Bottom parameter, VPB. The actual value of the
	      viewport top edge used in the plot may be less than
	      the value of VPT, depending on the setting of the
	      Viewport Shape parameter, VPS.  You must initialize
	      Vectors with a call to VVINIT after modifying this



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      parameter. The default value of VPT is 0.95.

       VRL - Vector Reference Length - Real
	      Use this parameter to specify the realized length
	      of the reference magnitude vector as a fraction of
	      the viewport width. Based on this value a reference
	      length in NDC units is established, from which the
	      length of all vectors in the plot is derived. The
	      relationship between magnitude and length also
	      depends on the setting of the minimum vector
	      magnitude fraction parameter, VFR, but, given the
	      default value of VFR (0.0), the length of each
	      vector is simply proportional to its relative
	      magnitude. Note that the arrow size parameters, AMN
	      and AMX, allow independent control over the minimum
	      and maximum size of the vector arrowheads.

	      Given a reference length, Vectors calculates a
	      maximum length based on the ratio of the reference
	      magnitude to the larger of the maximum magnitude in
	      the data set and the reference magnitude itself.
	      This length is accessible in units of NDC via the
	      read-only parameter, DMX. If VRL is set less than
	      or equal to 0.0, VVINIT calculates a default value
	      for DMX, based on the size of a grid box assuming a
	      linear mapping from grid coordinates to NDC space.
	      The value chosen is one half the diagonal length of
	      a grid box. By retrieving the value of DMX and
	      calling GETSET to retrieve the viewport boundaries
	      after the call to VVINIT, you can make relative
	      adjustments to the vector length, as shown by the
	      following example, where the maximum vector length
	      is set to 1.5 times its default value:

	       CALL VVINIT(...
	       CALL VVGETR('DMX - NDC Maximum Vector Size', DMX)
	       CALL GETSET(VL,VR,VB,VT,UL,UR,UB,UT,LL)
	       VRL = 1.5 * DMX / (VR - VL)
	       CALL VVSETR('VRL - Vector Realized Length', VRL)
	       CALL VVECTR(...

	      When VVECTR sees that VRL is greater than 0.0, it
	      will calculate a new value for DMX. If VRL is never
	      set, the initially calculated value of DMX is used
	      as the reference length. Do not rely on the
	      internal parameters used for setting the viewport,
	      VPL, VPR, VPB and VPT to retrieve information about
	      viewport in lieu of using the GETSET call. These
	      values are ignored entirely if the SET parameter is
	      zero, and even if used, the viewport may be
	      adjusted from the specified values depending on the
	      setting of the viewport shape parameter, VPS. See
	      also the descriptions of VFR, VRM, and VHC. The
	      default value of VRL is 0.0.



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


       VRM - Vector Reference Magnitude - Real
	      The introduction of the parameter VRM means that it
	      is now possible to specify an arbitrary vector
	      magnitude as the reference magnitude appearing in
	      the "Maximum Vector Text Block" annotation. The
	      reference magnitude no longer needs to be greater
	      or equal to the largest magnitude in the data set.
	      When VRM has a value greater than 0.0, it specifies
	      the magnitude of the vector arrow drawn at the
	      reference length. See VRL for an explanation of how
	      the reference length is determined. If VRM is less
	      than or equal to 0.0, the reference magnitude is
	      determined by the value of VHC, the vector high
	      cutoff value. If, in turn, VHC is equal to 0.0 the
	      maximum magnitude in the vector field data set
	      becomes the reference magnitude. The default value
	      of VRM is 0.0.

       VST - Vector Statistics Output Flag - Integer
	      If VST is set to one, VVECTR writes a summary of
	      its operation to the default logical output unit,
	      including the number of vectors plotted, number of
	      vectors rejected, minimum and maximum vector
	      magnitudes, and if coloring the vectors according
	      to data in the scalar array, the maximum and
	      minimum scalar array values encountered. Here is a
	      sample of the output:

	       VVECTR Statistics
				   Vectors plotted:  906
	       Vectors rejected by mapping routine:  0
		   Vectors under minimum magnitude:  121
		    Vectors over maximum magnitude:  0
			 Other zero length vectors:  0
			   Rejected special values:  62
		  Minimum plotted vector magnitude:  9.94109E-02
		  Maximum plotted vector magnitude:	 1.96367
			      Minimum scalar value:	-1.00000
			      Maximum scalar value:	 1.00000

       VSV - V Array Special Value - Real
	      VSV is the V vector component array special value.
	      It is a value outside the range of the normal data
	      used to indicate that there is no valid data for
	      this grid location. When SVF is set to 2 or 3,
	      Vectors will not draw a vector whose V component
	      has the special value. You must initialize Vectors
	      with a call to VVINIT after modifying this
	      parameter. It has a default value of 1.0 E12.


       WBA - Wind Barb Angle - Real

	      WBA sets the angle of the wind barb ticks in



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      degrees as measured clockwise from the vector
	      direction. It also sets the angle between the
	      hypotenuse of the triangle defining the pennant
	      polygon and the vector direction. You can render
	      southern hemisphere wind barbs, which by
	      convention, have their ticks and pennants on the
	      other side of the shaft, by setting WBA to a
	      negative value. WBA has an effect only when AST has
	      the value 2.


       WBC - Wind Barb Calm Circle Size - Real

	      WBC sets the diameter of the circle used to
	      represent small vector magnitudes (less than 2.5)
	      as a fraction of the overall wind barb length (the
	      value of the VRL parameter). WBC has an effect only
	      when AST has the value 2.


       WBD - Wind Barb Distance Between Ticks - Real

	      WBD sets the distance between adjacent wind barbs
	      ticks along the wind barb shaft as a fraction of
	      the overall wind barb length (the value of the VRL
	      parameter). Half this distance is used as the
	      spacing between adjacent wind barb pennants. Note
	      that there is nothing to to prevent ticks and/or
	      pennants from continuing off the end of the shaft
	      if a vector of high enough magnitude is
	      encountered. You are responsible for adjusting the
	      parameters appropriately for the range of
	      magnitudes you need to handle. WBD has an effect
	      only when AST has the value 2.


       WBS - Wind Barb Scale Factor - Real

	      WBS specifies a factor by which magnitudes passed
	      to the wind barb drawing routines are to be scaled.
	      It can be used to convert vector data given in
	      other units into the conventional units used with
	      wind barbs, which is knots. For instance, if the
	      data are in meters per second, you could set WBS to
	      1.8974 to create a plot with conventional knot-
	      based wind barbs. Note that setting WBS does not
	      currently have any effect on the magnitude values
	      written into the maximum or minimum vector legends.
	      WBS has an effect only when AST has the value 2.


       WBT - Wind Barb Tick Size - Real

	      WBT the length of the wind barb ticks as a fraction



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      of the overall length of a wind barb (the value of
	      the VRL parameter). The wind barb length is defined
	      as the length of the wind barb shaft plus the
	      projection of a full wind barb tick along the axis
	      of the shaft. Therefore, increasing the value of
	      WBT, for a given value of VRL has the effect of
	      reducing the length of the shaft itself somewhat.
	      You may need to increase VRL itself to compensate.
	      WBT also sets the hypotenuse length of the triangle
	      defining the pennant polygon. WBT has an effect
	      only when AST has the value 2.


       WDB - Window Bottom - Real
	      When VVINIT does the call to SET, the parameter WDB
	      is used to determine argument number 7, the user Y
	      coordinate at the bottom of the window. If WDB is
	      not equal to WDT, WDB is used. If WDB is equal to
	      WDT, but YC1 is not equal to YCN, then YC1 is used.
	      Otherwise, the value 1.0 is used. You must
	      initialize Vectors with a call to VVINIT after
	      modifying this parameter. The default value of WDB
	      is 0.0.

       WDL - Window Left - Real
	      When VVINIT the call to SET, the parameter WDL is
	      used to determine argument number 5, the user X
	      coordinate at the left edge of the window. If WDL
	      is not equal to WDR, WDL is used. If WDL is equal
	      to WDR, but XC1 is not equal to XCM, then XC1 is
	      used. Otherwise, the value 1.0 is used. You must
	      initialize Vectors with a call to VVINIT after
	      modifying this parameter. The default value of WDL
	      is 0.0.

       WDR - Window Right - Real
	      When VVINIT does the call to SET, the parameter WDR
	      is used to determine argument number 6, the user X
	      coordinate at the right edge of the window. If WDR
	      is not equal to WDL, WDR is used. If WDR is equal
	      to WDL, but XCM is not equal to XC1, then XCM is
	      used.  Otherwise, the value of the VVINIT input
	      parameter, M, converted to a real, is used. You
	      must initialize Vectors with a call to VVINIT after
	      modifying this parameter. The default value of WDR
	      is 0.0.

       WDT - Window Top - Real
	      When VVINIT does the call to SET, the parameter WDB
	      is used to determine argument number 8, the user Y
	      coordinate at the top of the window. If WDT is not
	      equal to WDB, WDT is used. If WDT is equal to WDB,
	      but YCN is not equal to YC1 then YCN is used.
	      Otherwise, the value of the VVINIT input parameter,



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      N, converted to a real, is used.	You must
	      initialize Vectors with a call to VVINIT after
	      modifying this parameter. The default value of WDT
	      is 0.0.

       XC1 - X Coordinate at Index 1 - Real
	      The parameter XC1 specifies the X coordinate value
	      that corresponds to a value of 1 for the first
	      subscript of the U, V, vector component arrays as
	      well as for the P scalar data array, if used.
	      Together with XCM, YC1, and YCN it establishes the
	      mapping from grid coordinate space to data
	      coordinate space. If XC1 is equal to XCM, 1.0 will
	      be used. You must initialize Vectors with a call to
	      VVINIT after modifying this parameter. The default
	      value of XC1 is 0.0.

       XCM - X Coordinate at Index M - Real
	      The parameter XCM specifies the X coordinate value
	      that corresponds to the value of the VVINIT input
	      parameter, M, for the first subscript of the U and
	      V vector component arrays as well as for the P
	      scalar data array, if used.  Together with XC1,
	      YC1, and YCN it establishes the mapping from grid
	      coordinate space to data coordinate space. If XC1
	      is equal to XCM, the value of M, converted to a
	      real, will be used. You must initialize Vectors
	      with a call to VVINIT after modifying this
	      parameter. The default value of XCM is 0.0.

       XIN - X Axis Array Increment (Grid) - Integer
	      XIN controls the step size through first
	      dimensional subscripts of the U,V vector component
	      arrays and also through the P scalar data array if
	      it is used. For dense arrays plotted at a small
	      scale, you could set this parameter to a value
	      greater than one to reduce the crowding of the
	      vectors and hopefully improve the intelligibility
	      of the plot. The grid point with subscripts (1,1)
	      is always included in the plot, so if XIN has a
	      value of three, for example, only grid points with
	      first dimension subscripts 1, 4, 7... (and so on)
	      will be plotted. See also YIN. You must initialize
	      Vectors with a call to VVINIT after modifying this
	      parameter. The default value of XIN is 1.

       YC1 - Y Coordinate at Index 1 - Real
	      The parameter YC1 specifies the Y coordinate value
	      that corresponds to a value of 1 for the first
	      subscript of the U, V, vector component arrays as
	      well as for the P scalar data array, if used.
	      Together with YCN, XC1, and XCM it establishes the
	      mapping from grid coordinate space to data
	      coordinate space. If YC1 is equal to YCN, 1.0 will



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Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      be used. You must initialize Vectors with a call to
	      VVINIT after modifying this parameter. The default
	      value of YC1 is 0.0.

       YCN - Y Coordinate at Index N - Real
	      The parameter YCN specifies the Y coordinate value
	      that corresponds to the value of the VVINIT input
	      parameter, N, for the second subscript of the U and
	      V vector component arrays as well as the P scalar
	      data array, if used.  Together with YC1, XC1, and
	      XCM it establishes the mapping from grid coordinate
	      space to data coordinate space. If YC1 is equal to
	      YCN, the value of N, converted to a real, will be
	      used. You must initialize Vectors with a call to
	      VVINIT after modifying this parameter. The default
	      value of YCN is 0.0.

       YIN - Y Axis Array Increment (Grid) - Integer
	      YIN controls the step size through the second
	      dimension subscripts of the U and V vector
	      component arrays and also through the P scalar data
	      array if it is used. For dense arrays plotted at a
	      small scale, you could set this parameter to a
	      value greater than one to reduce the crowding of
	      the vectors and hopefully improve the
	      intelligibility of the plot. The grid point with
	      subscripts (1,1) is always included in the plot, so
	      if YIN has a value of three, for example, only grid
	      points with second dimension subscripts 1, 4, 7...
	      (and so on) will be plotted. See also XIN. You must
	      initialize Vectors with a call to VVINIT after
	      modifying this parameter. The default value of YIN
	      is 1.

       ZFC - Zero Field Text Block Color - Integer
	      If ZFC is greater or equal to zero, it specifies
	      the GKS color index to use to color the Zero Field
	      text block.  Otherwise the Zero Field text block is
	      colored using the current GKS text color index. The
	      default value of ZFC is -1.

       ZFP - Zero Field Text Block Positioning Mode - Integer
	      The ZFP parameter allows you to justify, using any
	      of the 9 standard justification modes, the Zero
	      Field text block unit with respect to the position
	      established by the parameters, ZFX and ZFY The
	      position modes are supported as follows:

	      Mode	     Justification

	      -4	     The lower left corner of the text
			     block is positioned at ZFX, ZFY.

	      -3	     The center of the bottom edge is



UNIX			    April 1993			       32





Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


			     positioned at ZFX, ZFY.

	      -2	     The lower right corner is positioned
			     at ZFX, ZFY.

	      -1	     The center of the left edge is
			     positioned at ZFX, ZFY.

	      0 (default)    The text block is centered along
			     both axes at ZFX, ZFY.

	      1		     The center of the right edge is
			     positioned at ZFX, ZFY.

	      2		     The top left corner is positioned at
			     ZFX, ZFY.

	      3		     The center of the top edge is
			     positioned at ZFX, ZFY.

	      4		     The top right corner is positioned
			     at ZFX, ZFY.

       ZFS - Zero Field Text Block Character Size - Real
	      ZFS specifies the size of the characters used in
	      the Zero Field graphics text block as a fraction of
	      the viewport width. The default value is 0.033.

       ZFT - Zero Field Text String - Character* 36
	      Use ZFT to modify the text of the Zero Field text
	      block.  The Zero Field text block may appear
	      whenever the U and V vector component arrays
	      contain data such that all the grid points
	      otherwise eligible for plotting contain zero
	      magnitude vectors. Currently the string length is
	      limited to 36 characters. Set ZFT to a single space
	      (' ') to prevent the text from being displayed. The
	      default value for the text is 'Zero Field'.

       ZFX - Zero Field Text Block X Coordinate - Real
	      ZFX establishes the X coordinate of the Zero Field
	      graphics text block as a fraction of the viewport
	      width. Values less than 0.0 or greater than 1.0 are
	      permissible and respectively represent regions to
	      the left or right of the viewport. The actual
	      position of the block relative to ZFX depends on
	      the value assigned to the Zero Field Positioning
	      Mode parameter, ZFP. The default value is 0.5.

       ZFY - Zero Field Text Block Y Coordinate - Real
	      ZFY establishes the Y coordinate of the minimum
	      vector graphics text block as a fraction of the
	      viewport height.	Values less than 0.0 or greater
	      than 1.0 are permissible and respectively represent



UNIX			    April 1993			       33





Vectors_params(3NCARG)	  NCAR GRAPHICS	   Vectors_params(3NCARG)


	      regions below and above the viewport. The actual
	      position of the block relative to ZFY depends on
	      the value assigned to the Zero Field Positioning
	      Mode parameter, ZFP. The default value is 0.5.

SSEEEE AALLSSOO
       Online: vectors, vvectr, vvgetc, vvgeti, vvgetr, vvinit,
       vvrset, vvsetc, vvseti, vvsetr.	vvudmv, vvumxy,
       ncarg_cbind.

       Hardcopy: NCAR Graphics Fundamentals, UNIX Version

CCOOPPYYRRIIGGHHTT
       Copyright (C) 1987-2000
       University Corporation for Atmospheric Research

       This documentation is free software; you can redistribute
       it and/or modify it under the terms of the GNU General
       Public License as published by the Free Software
       Foundation; either version 2 of the License, or (at your
       option) any later version.

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       useful, but WITHOUT ANY WARRANTY; without even the implied
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UNIX			    April 1993			       34


