A common problem facing POVers is how to difference (ouch, that
shouldn't be a verb!) a bunch of CSG objects from another one, without
taking hours and hours to render.
Mike Williams has a great tutorial (
http://www.econym.demon.co.uk/holetut/ ) that talks about two of the
methods (subdividing the object and using isosurfaces). Another handy
method is to use blobs with negative strength component.
In the first and second pictures I created a blob with a big, flat
sphere and a bunch of negative cylinders, and then intersected the
result with a box. Render times were under 2 minutes, and, as the
second picture shows, an advantage is that you don't need regularly
spaced holes (as you would with the subdivision method.)
The third picture shows why I was needing a quicker difference. I've
been modeling "milling processes," where a milling tool rotates and cuts
pieces out of a block. If the block is a cylinder or a box, the
subdivision method works fine, with a little prep work, but when you're
carving out of some more irregularly shaped thing, this negative blob
method is much easier. In the fourth picture, I put the milling union
back in (slightly smaller) as a separate blob, to see how the carving
was done.
If anyone's interested, I can post the sources to PBSF or PTSF.
Dave Matthews
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