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

guillaume laforge guillaume at alamaison.fr
Wed Oct 21 15:11:50 EDT 2009


François :so the info was not so hidden in the doc :). Thanks again for the
links.
Ivan :
I tried to subdivide the sphere but it doesn't help much. It was not a
primitive sphere as UVs were needed.

If you download my sample scene, you will see that I moved the camera to the
center of the world and that the surface artifacts are close to the center
of world too.
I'm not sure it is a floating point error.

Andrew :
I'm not 100% sure but in one of my test to remove those artifacts(before
François help me with the vm_measure parameter),
I tried to scale down my big sphere by parenting all objects under a null
scaled down to 0.01. As It doesn't help, I created a new object and get the
scalled down sphere using an object merge. From this new object the shading
was better. I guess some transformation are more accurate at sop level ?

Cheers

Guillaume


On Wed, Oct 21, 2009 at 7:50 PM, Francois Duchesneau <sidefx at trinix.ca>wrote:

> http://www.sidefx.com/docs/houdini10.0/rendering/dicing
> http://www.sidefx.com/docs/houdini10.0/props/mantra10_0
>
> > It works :)
> >
> > I tried to add and tweak randomly different combination but didn't get
> the
> > good one.
> >
> > Is there any doc about all those dicing parameters ?
> >
> > Thanks a lot Francois !!!
> >
> > Cheers
> >
> > Guillaume
> >
> > On Wed, Oct 21, 2009 at 6:48 PM, Francois Duchesneau
> > <sidefx at trinix.ca>wrote:
> >
> >> If you add the vm_measure to your object and set it to "Uniform
> >> Measuring", the problem goes away. It's probably less efficient because
> >> it
> >> will have to dice too much far away.
> >>
> >> Let's hope it won't introduce artifacts elsewhere.
> >>
> >> François
> >>
> >> > 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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> >> >> >>
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> >> >>
> >> >>
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