INSTALL.plplot

  GDL creates graphical content using the support libraries of plplot, which relies on the use of 
some ASCII files.  Under many circumstances, these files are located successfully from the
information built into the program.  However other situations require a small extra step to
incorporate these.  For the windows' distribution a directory has been created to hold the files,
 and environment variables need to be set to point to these directories.

These directories are created when plplot is installed, located as follows:
<install prefix>/lib/plplot5.13.0/drivers for PLPLOT_DRV_DIR
<install prefix>/share/plplot5.13.0       for PLPLOT_LIB

the PLPLOT_LIB directory contains font info and color map info; the PLPLOT_DRV_DIR
directory provides the <driver>.driver_info used in dynamically linking the drivers.
For GDL distribution, where the plplot install directory may be absent or in an unknown location,
it is convenient to separately place these directories in a visible spot.  So a directory
named "plplot5.13" is created and the useful data copied into its subdirectories:

PLPLOT_LIB=plplot5.13/lib
PLPLOT_DRV_DIR=plplot5.13/drivers

Generally the driver shareable images (.dll) files are also found in the drivers directory;
the file used is the one found in the PATH, so either PATH is modified or the drivers can
be copied to an active PATH directory.