What is ZXPLOT?

ZXPLOT is a vector based graphics package developed by Ming Xue and Zuojun Zhang. ZXPLOT performs tasks ranging from the definition of plotting space, axis annotation, character string writing, curve plotting to the 2-D wind vector and scalar contour field plotting as well as color fill in between contours. Most of these features are available with NCAR Graphics, but ZXPLOT offers an additional degree of flexibility and ease of use. Here is an incomplete list of ZXPLOT capabilities:

2-D X-Y curve plotting, with axis labeling,
Contouring on an irregular grid (such as the vertical cross section of a terrain-following model grid) with user controls over the labeling,
Vector field plotting,
3-D surface plotting,
Text plotting with choices of fonts, picture coordinate transformations, masking, and window clipping.

The contouring subroutines in ZXPLOT allow a user to

set the limits on the maximum and minimum number of contours to be plotted,
allow the contour interval to be internally adjusted or kept at a prespecified value,
define the intensity of labeling,
adjust the way contours are highlighted,
choose the line pattern,
specify the line pattern of zero contours or suppress zero contours,
redefine the reference contour,
plot contours at irregular intervals,
hatch between contours,
perform gray-scale shading or color fill in between contours.

The graphics analysis program, ARPSPLT, used by the Advanced Regional Prediction System of the Center for Analysis and Prediction of Storms is based exclusively on ZXPLOT.

Two low-level interfaces for ZXPLOT are currently available - one calls a few low-level NCAR Graphics routines and produces CGM (computer graphics metafile) output compatible with the NCAR graphics output and the related tools (e.g., ctrans). This interface requires that NCAR graphics library be available. The interface routines are included in file xncar.f and the source code is freely available with the ZXPLOT object library distribution.

The other interface produces, independent of any other software package, PostScript files that can be viewed using PostScript viewers such as Ghostview or printed on a PostScript printer. In this case, no other graphic library is required for ZXPLOT to work. The PostScript interface routines are included in xpost.f and are freely available for users who may be interested modifying the code. The PostScript output has a few advantages: it is an ASCII file, therefore is device independent, it can be printed on any PostScript printer with high quality output, and the laser printer fonts are used for the text.

Another low-level interface is being developed that calls Xlib routines, so that the graphic output is directly sent to the X-window display. This will provide an interactive capability for ZXPLOT.