VVUDMV - This routine is the user-definable external subroutine used to draw masked vectors. The default

       To use VVUDMV, load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c, preferably in that order.

       Copyright (C) 1987-2009
       University Corporation for Atmospheric Research
       The use of this Software is governed by a License Agreement.

UNIX                                               April 1993                                     VVUDMV(3NCARG)

       XCS         (REAL  array,  assumed  size  NCS,  input): Array of X coordinates of the points defining the
                   polyline with the given set of area identifiers.

       YCS         (REAL array, assumed size NCS, input): Array of Y coordinates  of  the  points  defining  the
                   polyline with the given set of area identifiers.

       NCS         (INTEGER,  input):  Number  of points; assumed size of the X and Y coordinate arrays, XCS and
                   YCS.

       IAI         (INTEGER array, assumed size NAI,  input):  Array  of  area  identifier  values.  Each  value
                   represents  the  area  identifier with respect to the area group in the area group array with
                   the same array index.

       IAG         (INTEGER array, assumed size NAI, input): Array of area-identifier groups.

       NAI         (INTEGER, input): Number of area identifier groups. The current version of  Vectors  supports
                   up to 64 area groups.

       Use the ncargex command to see the following relevant examples: ffex05, vvex01.

       VVUDMV - This routine is the user-definable external subroutine used to draw masked vectors. The default
       version of the routine draws any polyline all of whose area identifiers are greater than or equal to
       zero.

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

       Hardcopy: NCAR Graphics Fundamentals, UNIX Version

       CALL VVUDMV (XCS,YCS,NCS,IAI,IAG,NAI)

       ´VVUDMV´  is  the  name given to the default version of the masked vector drawing routine, and it is also
       the name given to the argument through which the external subroutine is passed to  VVECTR.  However,  you
       may  choose  any  acceptable FORTRAN identifier as the name of a user-defined version of the routine. The
       substitute routine must have an argument list equivalent to the default version of VVUDMV. Also,  whether
       or  not  the  default  version  is  used,  the  subroutine  that  calls VVECTR should contain an external
       declaration of the routine similar to the following:

               EXTERNAL VVUDMV

       If the MSK parameter is set to the value 1, specifying high precision masking, Vectors sends one set of X
       and Y polyline coordinate arrays to the area masking routine,  ARDRLN,  for  each  vector  arrow.  ARDRLN
       subdivides  the  polyline  into  pieces such that each smaller polyline has a single area identifier with
       respect to each area identifier group, then makes a call to VVUDMV for each polyline  piece.   While  the
       default  version  of  VVUDMV  only  checks to see that none of the area identifiers are negative, a user-
       defined version could perform more complicated decision processing based on knowledge of the  meaning  of
       specific area identifier groups and/or area identifier values.  Note that, before invoking VVUDMV, ARDRLN
       modifies the user coordinate space by making the following calls:

               CALL GETSET(VPL,VPR,VPB,VPT,WDL,WDR,WDB,WDT,LLG) CALL SET(VPL,VPR,VPB,VPT,VPL,VPR,VPB,VPT,1)

       These  calls  temporarily turn the user to NDC mapping into an identity, allowing the user to call any of
       the routines, CURVE, CURVED, or the GKS routine GPL, to render the polygon piece , without worrying about
       a possible non-identity mapping between user and world coordinates.

       If MSK has a value greater than 1, specifying low precision masking, Vectors calls the routine ARGTAI  to
       get  the  area identifiers with respect to the area identifier groups for a single point that locates the
       base position of the vector. Vectors then calls the VVUDMV routine itself, passing the coordinate  arrays
       for a complete vector arrow.  Thus, a vector arrow whose base position is within an area to be masked can
       be  eliminated,  but  an arrow whose base position is nearby, but outside, a masked area may intrude into
       the area. Also, in this case, since faster rendering is the goal, Vectors does not convert the coordinate
       arrays into normalized device coordinates and do the identity SET call. Therefore, the  user  should  use
       only  CURVE  or  CURVED  to render the polyline, unless there is no possibility of a non-identity user to
       world coordinate mapping.

       The current version of Vectors supports masked drawing with up to 64 area groups. Vectors will exit  with
       an error message if an area map with more than 64 groups is passed to it.