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In article <1992Sep10.220413.11698@ncar.ucar.edu> scheitln@ncar.ucar.edu (Tim Scheitlin) writes:
>I have a question about the Explorer IsosufaceLat2 module.
>Some of the polygons in the isosurfaces I am generating with this module 
>appear to have their normals pointing in the wrong direction.

That's rather peculiar, all the normals should be right or all should be
wrong.  What kind of graphics do you have, do you see the same behavior
on the original IsosurfaceLat, and is your input lattice curvilinear?

>My question is:  Is the problem I am having with incorrect normals 
>related to the bug in the original Marching Cubes algorithm?

No, that bug just causes polygons to be missing.  Normal generation is
entirely separate.

Here are my guesses:

1.  You have a curvilinear lattice that reflects on itself so that cells
can have two different "senses".

2.  The module has a bug in normal generation.  Quite possible, but it's
strange that we haven't seen it before.

3.  There is a bug in the rendering code or the GL.  Very unlikely, but
not out of the question.

Roy Hashimoto
hashimoto@sgi.com