GEMPAK Online Tutorial
16 GEMPAK Overlays
We've already seen a little of the overlaying capabilities
of GEMPAK. When the CLEAR is set to
YES, a new frame is created. With the XW device, loops were created
using stored frames.
When CLEAR is set to NO, graphics are drawn to the same frame
which allows the creation of complex graphics with data overlays.
When CLEAR=NO, satellite and radar
images are not dropped, since those images would obscure any graphics
alrady drawn. However, the navigation information from the SAT or
RAD projection is still accessed from those files, so that other
data can be drawn on top of images already in place using the same
projection.
YOU are responsible for ensuring that
the times of the data you overlay make sense. GEMPAK makes no
attempt to ensure that your 500mb map is for the same time as
a GOES-8 image for instance.
Some Overlay Hints
To avoid the title line overwriting the previous
title drawn, be sure to set the TITLE variable to
a different line.
Be cautious of cluttering.
When using filled areas as overlays, a COLOR
of 0 will prevent the filled area from blocking out graphics
beneath for the value associated with that COLOR.
In many cases you will want to use filled areas as the base image with
other values plotted on top.
When plotting graphs, be sure to define the X and Y ranges,
since the ranges of different parameters may be different.
Also be weary of scaling changes.
GEMPAK Online Tutorial