Paul Bourke <pdb### [at] swineduau> wrote in news:pdb_NOSPAM-
157### [at] netplexaussieorg:

> 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?


If you use your density function/data to render an isosurface in POV-Ray,
then you can define another function that calculates the dot product
stuff.

This second function can then be used to control a pigment_map or a
texture_map so that you get an "Angle Of Incidence" controlled texture
(e.g. with varying opacity).


For some sample code, see my recent post:

'Source code for "AOI textures for isosurfaces"'
-> povray.text.scene-files


Tor Olav

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