[Sidefx-houdini-list] Confused about ptransform(), wo_space(), ow_space() and rest position.

Vinz ubik.lists at noos.fr
Fri Aug 13 09:14:42 EDT 2010


Hi,

I'm a bit confused about spaces transforms in a vop surface.

First I tried the transform vop, which uses the ptransform() function.
This one works as expected, from what I understand, in a vop surface, 
the current space is camera space, and if I transform the P in the vop 
from camera space to object space I get the expected result (same P as 
in SOP).


Then I noticed that the rest position node, when no attribute rest 
exists, uses a uvspace change which itself corresponds to 
wo_space()/wt_space()/toNDC().

The wo_space() and wt_space() function give me the same result, which is 
the same as ptransform("space:camera", "space:object").
And this is what I don't understand at all.

The help says for wo_space() : transforms a position value from World to 
Object space.
for wt_space() : transforms a position value from World to Texture space.

What's the difference between these two ? And it looks like they 
transform from camera to object space and not from world to 
object/texture space.


Thanks a lot for clearing things up,
Vincent




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