lighting/opacity question

harsh at harsh at
Wed Jun 23 13:08:21 EDT 1999


I'm not understanding something about lighting/opacity, at least I'm not
getting the results I'm expecting. I have forty data files representing a
volume changing over time. ( a timestep per file). I read the data files
in order, extract three surfaces using marching cubes, assign each surface 
a color and an opacity so I can see thru the object, and display these three
surfaces. I works fine if I just read and display the data looking down the z
axis. What I'd like to do is to move around the object. The approch I've been
trying is to move the camera every time step. I have a light defined. I set the
light's position to the camera position after moving the camera. I also
recompute the viewplane normals after the camera and light moves.When I'm on
the "front" of the object I can see thru the object .e.g., the object is sort of
like a cone, wher there is one surface it is light blue, where there are two
surfaces it is a darker blue. But when I'm on the back of the object I see only
light blue or a single surface. Also at 90 and 270 degrees there is a mottled
look to the surfaces.

I have a mpeg file if the above discription isn't clear. 

Any ideas??


Jim Harsh  E-Mail: harsh at
Los Alamos National Laboratory, MS P940
Los Alamos, NM 87545
505-665-0485, FAX - 505-665-3359
Date: 23-Jun-99,Time: 09:38:44

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