viewing matrix and feedback mode

[Thomas E Reed]

USER:  Randy Blaschke
       Bell Helicopter
       Arlington TX
       (817) 280-5860

Has asked me to post this request for information.

He is having a problem using feedback mode on a 4D80/GT rev 3.1C.

He is using feedback mode to select the nearest of a group of overlapping
triangular polygons.

The problem is closely tied to the viewing matrix being used.

Feedback mode will return incorrect z-values at times. However by changing
the viewing matrix ala the "ortho" and "polarview" commands the problem
will go away. It seems to improve by shifting the object nearer the far
clipping plane. We isolated it to the viewing matrix but haven't gone much
farther since changing the viewing parameters somewhat fixes the problem.

Has anyone had similar troubles?
Does anyone have a possible explanation?
Any input on feedback mode is welcome.

You can call Randy directly or mail me and I will forward it.
  

					 thanks in advance....
--

					Tom Reed
					SGI - Dallas

				     email: treed at sgidallas@sgi.com
				     vmail: 8705
				     phone: 214-788-4122