[Sidefx-houdini-list] Shading artifact when really close to surface

François Duchesneau sidefx at trinix.ca
Wed Oct 21 08:48:41 EDT 2009

I ran into similar issues too.

I wanted to render a pre-fractured ground with camera projection but 
many artifacts were visible around the seams. After many hours of 
research I tested the same in Maya and it worked so I decided to test it 
with Ray Tracing in Mantra and like you the problem disappear. My 
geometry had a big scale too and was also tangent to the camera. Maybe 
there are some tesselation settings out there in the properties to try out.

I thought it might be an issue with micro-polygon but honestly I'd be 
surprised RenderMan had the same issue. Unfortunately I don't have it to 
test it.

Out of curiosity, I guess if you recreate that kind of render in a 
smaller scale with a non-scaled camera you won't find any artifact. I'm 
asking because one day I had to scale a whole scene including the camera 
and a volume and I had to increase the volume sample a lot to make it 
render at a reasonable time.

Good luck and let me know if you find anything.


guillaume laforge wrote:
> Hi,
> I've got some shading artifacts when using micropolygon rendering with a
> camera really close to a geometry.
> The camera is tangent to the surface of a sphere. The sphere radius is 6371
> unit with a white lambert shader.
> When the camera distance to the surface is around four units, some patterns
> appeared in the shading of the sphere.
> At a distance of one unit, it is really "bumpy" !
> If I'm rendering polygons as subdivision surfaces it is worst (and when need
> to render this way).
> If I increase the shading quality, it is worst too.
> If I switch to Raytracing renderer, the problem disappear. Unfortunately we
> need to use Micorpolygon Rendering for this project.
> I tried to scale down all the scene but it doesn't work. I guess the problem
> came form the ratio between sphere radius and camera/surface distance being
> too big...
> Is there any magic settings to remove this kind of artifact, or is it a
> precision limitation of the micropolygon system.
> Thanks for any advice,
> Cheers.

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