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

Francois Duchesneau sidefx at trinix.ca
Wed Oct 21 12:48:19 EDT 2009


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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