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

guillaume laforge guillaume at alamaison.fr
Thu Oct 22 04:18:39 EDT 2009


For info, the scanline measuring set to "uniform" give a perfectly smoothed
surface but it is not usable if you need to change N and/or P in your
material...
You lost all the details of a displacement shader for example.

I also tried to use a sop transformation instead of objects transformation
but there is still some shading artifact.

Finally, as my surface (it is an ocean) is perturbed by a lot of noise, the
shading artifacts are not really distinguishable.

But this dicing problem is still a mystery to me...

Cheers

Guillaume

On Wed, Oct 21, 2009 at 9:11 PM, guillaume laforge
<guillaume at alamaison.fr>wrote:

> 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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