[Sidefx-houdini-list] camera projection mapping

Andrew D Lyons tstexture at gmail.com
Mon Jul 14 17:07:32 EDT 2008

Hi Jed,

You need to work with uv layering.

Look at:

group - prim grp by normal - backface from camera - if you only want
to effects uv's on front faces.
uv texture sop - choose project from camera. (the camera you will
render the still for painting from)
layer sop - has all kinds of controls for blending uv layers using masks etc.
attribute - to rename (store) incoming uv attrs and reinstate them on
output. Why? The uv texture sop will always work with uv layer 0. ie
"uv". You will often want to add a new layer (or blend with another
incoming uv layer). ie uv1 uv2 uv3 uv4 attrs. If you have all this in
a HDA, then the attr sop will let you rename uv to:
uv`ch("../uv_layer_id")` etc tc.
In your shader, use the matching uv layer for each texture. Blend
colors etc as needed.

Good luck!


2008/7/14 Jed Schwartz <jed at jedschwartz.com>:
> I'm exploring  the possibility of using camera projection mapping
> techniques (used quite successfully in a lightwave project) in our
> current production that calls for a bunch of extreme close up detail
> shots, mixed with broad sweeping moves across  very detailed martian
> terrain.  We have all our terrain built and a great set of very hi-
> res textures matching the DEMs we used to generate the terrain.
> Most of our shots are blocked out and approved for final render, so
> were to that stage where we're trying to figure out the most
> practical way to get detail into our shots where we need it- We have
> completed a few shots using Y projection maps with all the usual
> tiling, depth maps et-al- Very labor intensive and lots of extra
> detail generated that the camera will never see-
> My colleague who did this in lightwave breaks down his procedure into
> the following steps:
> 1. Finalize the camera move
> 2. Select "key" frames for terrain plate paintings
>   For a locked-off shot or a very small pan, one "key" painting
>   should be OK. For larger camera moves you may need to use several
>   paintings to cover the entire terrain seen by the camera. Instead
>   of using the (moving) final render camera I'll make a copy of it and
>   delete the motion so that each "key" painting camera is separate
>   and stationary.
> 3. Render a "screenshot" from the view of the plate camera
> 4. Paint on top of the screenshot
> 5. Project the final texture back through the plate camera onto the
>   terrain.
> The main reason to use this paint-projection technique is to get around
> the problem that ECU images never quite have enough resolution to
> look "photorealistic" for my typical MER shots. The disadvantage is
> the high amount of labor to set up each shot; the advantage is being
> able to put high-resolution detail exactly where it is needed for any
> given camera move.-
> I'd be most grateful if anyone who has explored this approach to
> projection mapping in Houdini and would be willing to share some
> insight into this process-
> Thanks!!
> Jed-
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Andrew D Lyons | Digital Artist | http://www.tstex.com

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