Provided by: libncarg-dev_6.3.0-6build1_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VELVCT is obsolete, and is supported only to provide compatibility with old NCAR Graphics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.