In article <c03t2ts9rc1r7ar0n3f5deje6aoh5pkmmb@4ax.com>, Defective 
<def### [at] homecom> wrote:

> Somewhere, long ago, I seem to recall seeing a macro for creating
> threads.  Now that I'm working on something with threaded parts, I
> can't find it and my own attempts at threading just don't work.

Well, I can't help with the macro, but threads are usually done with 
either a triangle mesh, a CSG with lots of small objects chopping away 
at or adding to a larger one in a spiral, or by using the parametric or 
isosurface objects in MegaPOV.

Using a parametric or isosurface would be the most memory efficient 
method, and can give smooth results. They can be slow, but that wouldn't 
be a problem unless the threaded part covers a large area of the final 
image.

It can be hard to get smooth shapes with the CSG technique, you have to 
use a large number of shapes to get it right, and it can be slow and 
memory consuming.

Meshes could be pretty fast and could be generated automatically with a 
macro, but can have visible "facets" if you don't use a high enough 
resolution, and can't be used in CSG (using CSG with meshes works in 
MegaPOV, but it isn't very reliable yet). Though they can use a lot of 
memory, copies of a mesh can use very little additional memory, because 
they can share data. Because screws and bolts have a very repetitive 
shape, a macro could make a basic "thread" shape like a short segment of 
a bolt, and use groups of these scaled and translated to make the actual 
screws/bolts very efficiently. That way, there would only be one basic 
"building block" that all the bolts in the scene could be constructed 
from, possibly saving a lot of memory.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

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