Greg, Since (I am told) hardware rendering works for this simple example, presumably a different algorithm is used there.
Thanks for your explanation. Gib > -----Original Message----- > From: Gregory D Abram [mailto:[EMAIL PROTECTED] > Sent: Friday, 10 August 2001 03:20 > To: [email protected] > Subject: Re: [opendx-users] Funny tetrahedron visualisation - > Volume Vis > > > > The problems you are seeing is inherant in the > volume-rendering algorithm > used by OpenDX, which is designed for large numbers of small > primitives, > rather than a few large primitives. It uses a back-to-front > algorithm in > which the faces of the primitives are composited over one > another taking > into account the distance in depth between the triangles. To > generate the > back-to-front ordering of the faces, OpenDX sorts them in Z > based on the > depth of the centroid of each face. Unfortunately, you don't > always get > the right answer - for that matter, there isn't always a right answer. > Consider two polygons in an orthographic projection : > > \ / > \ / > / > eye ----> Z / > / > / > / > / > > The \ triangle is in front of the / triangle, from the point > of view of the > eye, but the centroid of the / is shallower, so the > centroid-based depth > sort puts the / triangle in front of the \ triangle, which is wrong. > > > You can improve the situation by putting the Refine(level = 3 > or 4) in > front of Image, generating a lot of little tets from your two > big ones. > > Greg > > > NOTICE - This e-mail is only intended to be read by the named recipient. It may contain information which is confidential, proprietary or the subject of legal privilege. If you are not the intended recipient please notify the sender immediately and delete this e-mail. You may not use any information contained in it. Legal privilege is not waived because you have read this e-mail. For further information on the Beca Group of Companies, visit our web page http://www.beca.co.nz
