This is a diagnostic tool, used to show the contents of
"upstream geom" data types, sent upstream for interactive
control in AVS3.
It uses "user defined data types".
The AVS flow executive has a special case for effiently handling
upstream flow. The print modules do not send anything
to the geometry viewer, and are hand-wired in afterwards,
so the flow exec bypasses them.
1. Have your probe and other upstream modules run at least once,
so you know valid data is sitting at the GeomViewer output ports.
2. Get the print module to run, by tweeking a parameter (or add a
one-shot "look" button, just to get it to fire. Or use the
CLI to fire it, or make some port that you wire from an upstream
module, like probe, so probe will fire the print module.