View Full Version : UV unwrapping and ST in Renderman?

03 March 2003, 11:21 PM
I was wondering if someone could help me with understanding texturing coordinates and rewriting UV's in Renderman. Perhaps Mauritius..... There is a concept that renderman books out there don't seem to cover. I know that you can use projection methods such as spherical and conical projection. These may work fine for patches and Nurbs. However, how do you explain UV unwrapping polygonal objects for texturing which is done in programs like Maya, Max, and XSI. As far as I know UV mapping by hand gives the least amount of distortion for complex organic shapes like polygonal human heads. Are these programs in a sense rebuilding/reparameterizing the default UV coordinates so that it works out easier for the texture artist? Are UV's for mapping in Maya,Max,and XSI equivalent to S and T in renderman? Basically, I'm asking if the UV coordinates are reassigned/rewritten/renumbered as you layout your UV's by hand. I'm also asking if this new UV coordinate setup can be transferred from the "modeler program" to Renderman so that it understands the new UV/ST coordinate setup. Can Maxman/Mayaman/MTOR make this translation? Any help would be greatly appreciated.

03 March 2003, 11:28 AM
it should be no problem getting manipulated mapping coordinates
converted to RIB, for Polys and SubDs what you see in your App
is what you get in your render output. More tricky are different
mapping channels(Max) or UV sets(Maya)...because a second
group of varying floats (e.g. ST2) must be generated in your
RIB and used in the assigned shader.
Forget MayaMan and MaxMan they are not supported anymore
(i heard) and its not predictable how handwritten shader may
react on the strange RIB they are generating.
For Maya MTOR is very good and Liquid (Wetas converter) is opensource this means for free...

03 March 2003, 12:40 PM
Originally posted by Fex
Forget MayaMan and MaxMan they are not supported anymore
(i heard) and its not predictable how handwritten shader may
react on the strange RIB they are generating.

i don't know where you heard that, but mayaman is still supported very well, there was a new release just one week ago. and animallogic has a really great support, maybe the best i ever had for a 3d-programm.
what do you mean with "its not predictable how handwritten shader may
react on the strange RIB they are generating"?? i never had problems with any handwritten stuff (mostly the problems occured because of my code :rolleyes: ), and i also can't retrace in what way the mayaman-generated ribs should be strange!?

basically s,t are by default identical to u/v (means s=u, t=v), but they could be modified in the rib if you want to.

03 March 2003, 03:53 PM
@Flinch: sorry i tought the problems that MaxMan has
are equal to MayaMan...cause MaxMan does many
concat transforms that make it hard or sometimes impossible
to have clear defined shader spaces... causes trouble in
shaders with many layers of procedual textures

MTOR makes RMan features accessible in Maya while
Maya and MaxMan converts application features to RMan..

03 March 2003, 05:29 PM
@Fex: i don't know how bugfree and complete the last release of MaxMan was, so it could be that MaxMan has alot of bugs which aren't existent in MayaMan. it seems that animallogic isn't supporting MaxMan for a quite a while now.

i don't really know MTOR very well, but as far as i know MTOR makes RMan features accessible in Maya, but doesn't convert many of the maya features to RMan (which means you've to use slim to texture your objects and can't use the maya-tools. - please correct me if it's wrong-).

MayaMan on the other hand converts mayafeatures to RMan. therefore you can use nearly all mayatools, like hypershade or fur for example without the need of additional tools. but MayaMan not only converts application features to RMan, it also adds RMan features to Maya. therefore you've different MayaMan-Attributes which give you access to RMan features. e.g. you can build a shading-network in hypershade and you can add a sl-node to include sl-code in your shading-network.

03 March 2003, 06:12 PM
@Flinch: totally missed it you are from Munich too
:beer: prost

i used MaxMan for some projects but skipped it cause many
things work automaticly and couldn't be switch off
e.g. shadow maps are always generated from lights
camera and use all objects in scene, with MTOR everything
is much more precise and deeper accessible...
and SLIM is completly open (every node is a quite simple

Liquid should be faster at converting and powerful...we will
see :)

03 March 2003, 06:23 PM
RAT exports UVs and even multiple UVs from Maya's UV Texture Editor for use as ST coordinates in rendering polygon meshes and subdivision surfaces. If you have the docs check the modeling subdivision surfaces section.


03 March 2003, 08:49 PM
I find that if I use UV snapshot, then paint over it in photoshop, then apply it with the default st coordinate system in Slim, I have to rotate the image by 90 degrees ccw in Photoshop for it to look right!

03 March 2003, 10:50 PM
Thank you everyone for your replies. They were all very informative and helpful. Yeah, playmesumch00ns I heard that from some other fellow in another forum. He said he had to do the exact same thing! I don't know what's going on there either. Maybe the S is V and T is U instead of S-U, T-V. Perhaps a flipping occurred somewhere in the translation or Maya's default UV setup is a flipped version of the renderman ST coordinates. That's my best guess.:shrug:

03 March 2003, 12:34 AM
I think the order of them may be reversed just by definition. Something I remember vaguley from one of my maths lectures in NURBS. There's something in the RAT docs about the "natural parameterization" and having to rotate it by 270 degress or something with an ST matrix or somesuch, but that was to do with NURBS again.

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