I'm working on a project where I have a spacecraft modeled in inches, and
I'm putting it in a world scene (earth, sun, moon) that I have modeled in
kilometers.

So I scale my craft into kilometers with "scale .0000254".  Yikes, yes,
thats awful small. And many of the vertices have coordinates that small to
begin with. (So I do end up with a lot of degenerate triangles).

The problem is, when I scale that small, my renders go so slow they're
unusable.  When rendered in its native units (inches), a typical image
renders in about 40 minutes. Whereas when I scale it into kilometers, that
same image...well...it rendered for 17 hours until I killed it because it
wasnt even halfway done.

Whats the issue here?  What is MOST confusing, is on the last project, with
a very similar model file that was modeled in milimeters, I did a similar
scaling only MORE extreme (scale .000001), and that rendered fine!!  All on
the same machines with the same architecture (develop on Windows, render
animation frames on linux cluster, and yes the problem occurs on both
archs).

So, why does such a scale drop rendering to a crawl, and why did it NOT do
that when I was scaling with .000001 on the other project?

Yes, I can look into 64-bit archs, look into work arounds, find a happy
medium unit to work in, etc.  But I want to understand more clearly how
performance is being affected by this.

Any input?  Thanks in advance.

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