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

Francois Duchesneau sidefx at trinix.ca
Wed Oct 21 13:50:37 EDT 2009


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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