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

guillaume laforge guillaume at alamaison.fr
Wed Oct 21 11:29:35 EDT 2009


My scene is just a sphere :).

For info, here is a sample file showing the problem :
http://www.vol2nuit.fr/repro_shading_pb.hip

Cheers

Guillaume

On Wed, Oct 21, 2009 at 4:01 PM, Francois Duchesneau <sidefx at trinix.ca>wrote:

> In that case what I don't understand is if I'm creating a sphere with a
> radius of 1 with a close up camera aiming at the top of the sphere, I
> won't get artifacts.
>
> This means there's must be something in particular that causes this. In my
> case all the fractured piece of geometries were separated. Is your sphere
> made up of different polygons not fused together?
>
> François
>
>
> > 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.
> >
> > Cheers
> >
> > Guillaume
> >
> > 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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