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

Ivan DeWolf ivan at martian-labs.com
Wed Oct 21 13:10:06 EDT 2009

I found that if you get extremely close to a primitive so that it is  
larger than the field of view you run into problems. I was using one  
giant polygon out to the horizon for an ocean surface.

using a single sphere primitive and getting down under .1 percent of  
the radius off the surface sounds like a similar problem.

The solution I found was to subdivide the geometry so that there were  
no polygons sticking off more than one side of the camera at a time.  
For your sphere, I wouldn't use a sphere primitive, I'd try something  
like a polygonal sphere and group polygons that are close  to camera  
and subdivide 'em.....

or creep a grid or flat cylinder onto a sphere....

Quoting "guillaume laforge" <guillaume at alamaison.fr>:

> 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.
> --
> Guillaume Laforge
> 3D at la maison.
> http://www.alamaison.fr
> my blog : frenchdog.wordpress.com/
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