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> http://wiki.povray.org/content/Reference:Union#Split_Union
>
> OK ... narrative says it's used with photons, but made a typo and
> accidentally enabled on a tile floor (many tiles and grout) but I wasn't
> using photons. The object count went down like expected, but render time
> slowed to a crawl ... walked away from computer, and the usual 3 minute
> render had only managed to get almost through the first row. Like I said
> a mistake, and can't off the top of my head think of any use of
> split_union /without/ photons ... could it be that split_union should
> first check for photon usage then ignore the "on" setting if photons
> aren't used?
Normaly, unions are split into the individual component. It improve
bounding, making the scene render much faster. Each component have it's
own bounding box.
With split_union off, you are forced to evaluate the whole union, and
all of it's elements, for every ray that enter it's bounding box. You no
loner have the individual bounding boxes, bot only one large one.
You get something similar when you use merge or apply a manual bounding
on an union.
Alain
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