Provided by: libncarg-dev_6.4.0-9_amd64 
NAME
VELVCT - Plots a vector field, given two 2-dimensional vector component arrays, U and V. You may control
certain characteristics of the plot by adjusting the values given to the input arguments. Other less
frequently changed characteristics may be affected by modifying VELDAT, the BLOCK DATA routine that
initializes members of the common blocks VEC1 and VEC2. In addition, depending on the value given to the
compatibility parameter, CPM, you may set other options by calling VVSETC, VVSETI, or VVSETR to modify
internal parameters.
SYNOPSIS
CALL VELVCT (U,LU,V,LV,M,N,FLO,HI,NSET,LENGTH,ISPV,SPV)
STATUS
VELVCT is obsolete, and is supported only to provide compatibility with old NCAR Graphics codes. However,
the compatibility mode parameter, CPM, offers a number of options to help ease the the transition to the
new version of the utility. When writing new code you are encouraged not to use this entry point, since
it provides less capability than the standard Vectors interface, and may eventually be phased out.
C-BINDING SYNOPSIS
#include <ncarg/ncargC.h>
void c_velvct(float *u, int lu, float *v, int lv, int m,
int n, float flo, float hi, int nset,
int length, int ispv, float *spv)
DESCRIPTION
U (REAL 2-dimensional array, dimensioned LU x n: n >= N, input): By default, assumed to contain
the first dimensional Cartesian components of the vector field. However, if PLR is non-zero,
it is treated as containing the vector magnitudes.
LU (INTEGER, input): Actual value of the first dimension of array U.
V (REAL 2-dimensional array, dimensioned LV x n: n >= N, input): By default, assumed to contain
the second dimensional Cartesian components of the vector field. However, if PLR is non-zero,
it is treated as containing the vector angles.
LV LV (INTEGER, input): Actual value of the first dimension of array V.
M (INTEGER, input): Number of contiguous elements along the first dimensional axis containing
data to be processed in each of the arrays, U and V.
N (INTEGER, input): Number of contiguous elements along the second dimensional axis containing
data to be processed in each of the arrays, U and V.
FLO (REAL, input): Minimum vector magnitude allowed to be displayed in the plot.
HI (REAL, input): Maximum vector magnitude allowed to be displayed in the plot. If set to 0.0
there is no upper limit imposed.
NSET (INTEGER, input): Flag that controls how and when the SET call is invoked. If NSET is 0,
VELVCT makes a SET call to establish a standard viewport and window boundaries coincident
with the array coordinate boundaries. PERIM is called to draw a border. If NSET is greater
than zero, VELVCT does not call SET or PERIM. If NSET is less than zero, VELVCT calls SET to
establish window boundaries coincident with the array grid coordinate boundaries but does not
modify the viewport or call PERIM. Unlike the VVINIT/VVECTR interface, when VELVCT does a SET
call, it always restores the original coordinate system state before returning.
LENGTH (INTEGER, input): The length in plotter address units (PAUs) used to render the vector with
the greatest magnitude that is eligible for plotting. A vector is eligible for plotting if it
is less than or equal to the value of HI, unless HI is 0.0 in which case all vectors are
eligible. If LENGTH is set to 0.0, the length selected is one half the diagonal length of a
grid cell assuming a linear mapping of the grid coordinate space into the viewport.
ISPV (INTEGER, input): Flag to control the special value feature. 0 means that the feature is not
in use. 1 means that if the value of U(I,J)=SPV(1) the vector will not be plotted. 2 means
that if the value of V(I,J)=SPV(2) the vector will not be plotted. 3 means that if either
U(I,J)=SPV(1) or V(I,J)=SPV(2) then the vector will not be plotted. 4 means that if
U(I,J)=SPV(1) and V(I,J)=SPV(2), the vector will not be plotted.
SPV (REAL array, dimensioned 2, input): An array of length 2 which gives the value in the U array
and the value in the V array which denote special values. This argument is ignored if ISPV=0.
The default values are 1.0E12.
C-BINDING DESCRIPTION
The C-binding argument descriptions are the same as the FORTRAN argument descriptions with the following
exceptions:
lu The second dimension of u in the calling program.
lv The second dimension of v in the calling program.
m Number of contiguous elements along the second dimensional axis containing data to be
processed in each of the arrays, u and v.
n Number of contiguous elements along the first dimensional axis containing data to be
processed in each of the arrays, u and v.
USAGE
Beginning with version 3.2 of NCAR Graphics, the VELVCT entry point has been recoded as a front end to
the VVINIT/VVECTR interface to Vectors. The compatibility mode parameter, CPM, controls the degree to
which a call to the Version 3.2 VELVCT emulates the older call. Appropriate settings of CPM can
separately address each of the following three questions regarding the level of emulation:
• Should FX, FY, MXF, and MYF rather than the Version 3.2 mapping routines perform the mapping to
user coordinates?
• Should the input arguments FLO, HI, NSET, LENGTH, ISPV, SPV override the current values of the
corresponding Vectors' internal parameters?
• Should the values contained in the common blocks VEC1 and VEC2 override the current values of
corresponding Vectors' internal parameters?
Given the default value of CPM, all these questions are answered in the affirmative, and a call to VELVCT
gives a reasonably faithful emulation of the older version's behavior.
However, even in this case, it is possible to use the parameter setting routines to control the behavior
of features that have no counterpart in the older version of VELVCT, as long as the feature is accessible
without calling the new interface. For instance, you could control the vector linewidth by setting the
LWD parameter, although you could not draw vectors masked to an area map because doing so requires direct
invocation of VVECTR
The following two tables show how the VELVCT input arguments and VEC1/VEC2 common block members map into
internal parameters currently supported by Vectors. (Consult the vectors_params man page for descriptions
of the internal parameters.)
Input Argument Internal Parameter
FLO VLC (VLC is set to -FLO if FLO is positive, 0.0 otherwise)
HI VHC (VHC is set to -HI if HI is positive, 0.0 otherwise)
NSET SET (NSET = 0 is approximately equivalent to SET = 1)
LENGTH VRL (LENGTH in Plotter Address Units is converted to VRL as a fraction of
the viewport width)
ISPV SVF
SPV(1) USV
SPV(2) VSV
Common Block Member Internal Parameter
EXT VPS
ICTRFG VPO
ILAB LBL
IOFFD DPF
RMN AMN (RMN in metacode coordinates is converted to AMN as a fraction of the
viewport width)
RMX AMX (RMX in metacode coordinates is converted to AMX as a fraction of the
viewport width)
SIZE LBS (Character size in metacode coordinates is converted to LBS as a
fraction of viewport width)
INCX XIN
INCY YIN
- MNT (When common blocks VEC1 and VEC2 override parameter settings, MNT is
always set to " ", indicating that the minimum vector text block is not to
be displayed.)
IOFFM MXT (If IOFFM is non-zero, MXT is set to " ", indicating that the maximum
text block is not to be displayed. Otherwise MXT is set to the string
"MAXIMUM VECTOR")
IOFFM MXX (If IOFFM is 0, MXX is set to a computed value that, as a fraction of
the viewport width, specifies a point 0.05 in NDC left of the right hand
edge of the plotter frame.)
IOFFM MXY (If IOFFM is 0, MXY is set to a computed value that, as a fraction of
the viewport height, specifies a point 0.005 in NDC up from the bottom edge
of the plotter frame.)
IOFFM MXP (If IOFFM is 0, MXP is set to -2, indicating that the text block should
be lower-right justified.
Note that the emulation of the maximum vector text block differs from
the older implementation in that it now uses high-quality text.
EXAMPLES
Use the ncargex command to see the following relevant example: stex02, tvelvc.
ACCESS
To use VELVCT or c_velvct, load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c, preferably in
that order.
SEE ALSO
Online: vectors, vectors_params, fx, vvectr, vvgetc, vvgeti, vvgetr, vvinit, vvrset, vvsetc, vvseti,
vvsetr, vvudmv, vvumxy, ncarg_cbind.
COPYRIGHT
Copyright (C) 1987-2009
University Corporation for Atmospheric Research
The use of this Software is governed by a License Agreement.