UV Pelting

[mattc01223]

Hi houdini users

I've just seen on the home page a poll for new houdini features and one of them is UV Pelting. Where is this in Houdini and does it have anything to do with unwrapping polys when applying textures to a character (ie - animal pelt). And I'll say thanks now to anyone who knows the answer to this.

Matt

[Wolfwood]

In Houdini build 6.1.101 (at vislab) you can get to the pelter in SOPs. Its called UVPelt.

jim.

[Mcronin]

does it have anything to do with unwrapping polys when applying textures to a character (ie - animal pelt).

Matt

That's precisely what it does.

[Wolfwood]

does it have anything to do with unwrapping polys when applying textures to a character (ie - animal pelt).

Matt

That's precisely what it does.

In addition to this I've heard rumors that if you turn the iterations up high enough Houdini will actually spawn a beer in your hand.

jim.

[tallkien]

Hi All

can someone please post a simple hip demonstrating its use, or are there some docs you can point me to. Yet to figure this one out

thanks

[Mcronin]

Take a model and apply UV Pelt. The first thing you need to do is select boundary edges for the pelt, so select a closed loop of edges around your model. There are several hotkeys that will help you select a loop. If you select an edge and hit l, Houdini will try to select a loop around your model automaticly, ending at you currently selected edge. If you select an edge and use shift+l, houdini will try to select a loop as far as it can around the model, not necessarily ending at your selection. If you select an edge and start pressing f, houdini will begin walking the edges (selecting the next edge, one at a time, each time you hit f). Lastly if you hit the r key while walking edges, the direction in which you are walking th edges will be reversed.

Once you have selected an enclosed area to apply th pelt, you need to select a hint polygon. Now I could be completely misunderstanding what the hint polygon is, but what it seems to do is tell houdini what the internal area of the pelt is, and set an orientation in UV space. Hold control and left click on a polygon in the area you want to unwrap. You should see the edges in this area turn blue. If they don't, hit the g key. the g hotkey turns on the visualization of the pelt. If the blue edged area looks good to you right click.

Next UV Pelt asks for a frame face. This is totally optional. What this will do is allow you to select a polygon that will serve as a frame for the area you are unwrapping. I'm sorry that's convoluted, and I can't explain it better, but try it and see what happens it'll make perfect sense when you see it. Select a polygon and right click, or select nothing and right click. It's all up to you. If you select nothing you will end up with a circular frame.

Now pop open your UV viewport. In the UV Pelt's parameters page. Bring up the maximum iterations. You should now see your pelt in the UV viewport. Play around with the options so you can get a feel for what they all do, and realize if you go to the UV mapping tab in the Pelt SOP's parameters you can do some global UV adjustments to your pelt.

Hope this helps. Have fun.

[mattc01223]

Thanks for your help with this one - tried it on a simple model and it worked a treat!!

Looks like I'll have to get out my old box of paints and start making textures!!

Matt

[Mcronin]

Glad it worked for you. I played with it a bit myself just now, and I guess a good explanation for the frame face might be that the frame face defines the ultimate shape the pelt tries to achieve. It kinda works like a spring, like you are stretching canvas on a frame. The thing I don't like is it doesn't seem to let you choose an arbitrary group of faces to define a frame, and I don't see anyway to manipulate the frame. It might be useful to be able to define a frame that's shaped like, I dunno, a cross or something in some instances.

[edward]

The next public early access should have help. A little birdy tells me that it should be out sometime soon.

The second input accepts arbitrary frame geometry so that you could exactly do the shape you want.

You guys should really post about this on the Early Access Feedback forum at http://www.sidefx.com/forum so that the right people read about it.

[Mcronin]

Are you saying the current version of UV Pelt does this? Or the next rev will? I tried plugging arbitrary geometry into the second input and UVPelt went haywire on me. My frame face was a triangle, when I was giving it several quads in the shape of a cross. I thought it was maybe because I had mutliple faces feeding into the second input, so I dissolved all the interior edges to make it a big n-gon, and got the same result. This was in 6.1.101 BTW...

[tallkien]

Ah, I see now, Very interesting..

Thanks Mcronin,

frame face works fine for me with multiface selections (as long as they form a rect) on build 101, well mostly anyway, changing the hint primitive despite using frame geo occasionally sets things right... i think, much playing around needed

[tallkien]

Hi,

MichaelC posted an example scene on sidefx, here's a slightly modified version of the same file demo-ing how i think pelt might be used, as always suggestions and comments welcome

cheers

tallkien

--------------------

think hint primitive 67 and a higher spring constant makes more sense in this example

ofcourse normally you would use inconspicuous edges to cut

UVPeltExample_01.hipnc.gz

[rebo]

Im trying to use this method to UV a basic head. Im selecting around 10 edges that go from the crown to the base of the neck. For a frame face im selecting, a single grid face which faces the Z axis.

I have no idea how to choose a hint face.

Unfortunately the uv's when layed out are extremely squashed in the middle making it quite impossible to texture the head. Does anyone have an example where they have UV'd a basic head using UVpelt... Thanks.

[Mcronin]

Maybe this will help rebo and anyone else who is having trouble. I put together a quick walk through and have included an example head scene.

Page is here.

http://home.earthlink.net/~mdcronin1/UVPelt/index.htm

Scroll to the bottom and you'll fins a link to a zip containing the pelted head.

If anyone finds this useful and Marc or Jason wants to move this to the odforce tutorial section, that's fine with me. I can't keep it where it is forever.

Good Luck

[rebo]

Thanks Mcronin, I think the problem i have is to do with the topology of my head. i.e. its very detailed at the front but has only a few polys at the back. I reckon i can sort it via some uv editing.

The hint poly seems a strange way of implementing this tool. As all it seems to do is decide what section you are uving a the the orientation of that setion. I think it would be far more logical to choose an edge that you can orient the uvs to this way creating a symetrial pelt will be much easier.

I dont know if thats possible tho.

[Jason]

I linked this on the odforce main page.. I'll add it to the tutorials once it gets released and the tool is mature. I'm pretty sure that there are a few good ways to use pelting, in particular on diffrerent topology models.