Wasn't it Richard Kline who wrote:
>
>When I attempted to render the gravitation equipotential surface of two 
>bodies (i.e the surfaces of the double planet in Robert Forward's 
>"Flight of the Dragonfly"). The iso_surface object behaved oddly with 
>these three behaviors:
>
>1) If the contained_by shape is larger than the true surface for the 
>given threshold value, the entire contained_by shape (either box or 
>sphere) is rendered as part of the surface.
>
>2) If parts of the surface extend beyond the contained_by shape, you get 
>the difference of the contained_by shape and the true surface. (this is 
>shown in POVRay Example 1 below)
>
>3) If the contained_by shape is made large enough to contain the true 
>surface, camera, and light_source, you get the correct results for the 
>iso_surface, but it takes a long time to render since every point in the 
>scene has to be tested.
>

I confess to not having tried all your examples, but what you describe
sounds exactly like rendering the isosurface inside out.

See <http://www.econym.demon.co.uk/isotut/insideout.htm>

The "inside" of an isosurface is the region where the function minus the
threshold is less than zero and the outside is where it's greater than
zero. For some functions this may be different from what common sense
tells you should be the inside and outside.

Try using "isosurface {function {0 - Roche(x,y,z) }" and 
"threshold -2.0" to flip the thing right side out.

-- 
Mike Williams
Gentleman of Leisure

Post a reply to this message