I'm using PovRay to visualise the distribution of galaxies from a
recently completed survey. The starting point is the 3D position
of 1/4 million galaxies. The survey is in 2 wedges, see
   http://astronomy.swin.edu.au/~pbourke/tmp/2df/set4/plan.gif
Each dot is a galaxy.

I take a 100Mpc cube (in white in the above diagram) and map some
variable onto the galaxy position. I also derive a density function
and create a volumetric dataset which I can represent as such, see
   http://astronomy.swin.edu.au/~pbourke/tmp/2df/set2/points_gas_1.jpg
for example, or I can compute isosurfaces (marching cubes), see
   http://astronomy.swin.edu.au/~pbourke/tmp/2df/set4/hi_transp.jpg
and recently I've been making fishnet stockings
   http://astronomy.swin.edu.au/~pbourke/tmp/2df/set4/mesh2.jpg
(Sorry for the big picture).

So finally to my question. I would like to experiment with an isosurface
(current a huge bucket of triangles in a mesh) where the transparency
was proprotional (or some other function) to the angle between the
camera and the triangle normal. In particular, where the dot product
is low I want high transparency, where the dot product is large I
want a high opacity. I'm interested in representing the borders of the
isosurface while being able to see the objects inside.

Ideas?
-- 
Paul Bourke
pdb_NOSPAMswin.edu.au

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