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

guillaume laforge guillaume at alamaison.fr
Wed Oct 21 08:30:16 EDT 2009

Hi François,

Thanks for the info on your similar experience !

I tried to scale down all except the camera but it doesn't solve the problem

Btw, it is using 9.5.310. Didn't try in 10 yet.



2009/10/21 François Duchesneau <sidefx at trinix.ca>

> 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.
> François
> 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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