Bob,
Your guess is right. Radiance's triangles, even with normal
interpolation, are still flat. To use the normals to present a true curved surface would (I think) require an implicit representation of the surface.
This particular example, with a low-res mesh and direct sunlight, is the "poster-child" of this problem.
I usually avoid this problem by a combination of higher resolution (I use tri meshes up to 1M elements) and more ambient than direct light.
So, I see no way to completely avoid this for some problems.
Mark
mstock@umich.edu
···
On Tue, 13 Dec 2005, bob coyne wrote:
Hi,
I'm having a problem rendering polygon mesh objects with interpolated
vertex normals (converted via obj2mesh). I'm running Radiance 3.7.2b
patch release 22 Aug 2005.
When I render a sphere mesh that's illuminated from above and to the
side, I get bad artifacts along the shadow line, with large dark
triangular wedges periodically protruding into the illuminated
area. (See link below for what this looks like.) The dark triangles
seem to correspond to those quadrilaterals in the mesh where only a
single vertex is illuminated. My guess is that it's treating the whole
quad as pointing away from the light source, even though one vertex
and a significant area of it are in the illuminated region of the
object.
Is there any way to avoid this?
www.semanticlight.com/images/sphere-problem.jpg
Thanks for any help.
- Bob
_______________________________________________
Radiance-general mailing list
Radiance-general@radiance-online.org
http://www.radiance-online.org/mailman/listinfo/radiance-general
Mark, thanks for verifying that this was the problem.
- Bob
Mark Stock wrote:
···
Bob,
Your guess is right. Radiance's triangles, even with normal
interpolation, are still flat. To use the normals to present a true curved surface would (I think) require an implicit representation of the surface.
This particular example, with a low-res mesh and direct sunlight, is the "poster-child" of this problem.
I usually avoid this problem by a combination of higher resolution (I use tri meshes up to 1M elements) and more ambient than direct light.
So, I see no way to completely avoid this for some problems.
Mark
mstock@umich.edu
On Tue, 13 Dec 2005, bob coyne wrote:
Hi,
I'm having a problem rendering polygon mesh objects with interpolated
vertex normals (converted via obj2mesh). I'm running Radiance 3.7.2b
patch release 22 Aug 2005.
When I render a sphere mesh that's illuminated from above and to the
side, I get bad artifacts along the shadow line, with large dark
triangular wedges periodically protruding into the illuminated
area. (See link below for what this looks like.) The dark triangles
seem to correspond to those quadrilaterals in the mesh where only a
single vertex is illuminated. My guess is that it's treating the whole
quad as pointing away from the light source, even though one vertex
and a significant area of it are in the illuminated region of the
object.
Is there any way to avoid this?
www.semanticlight.com/images/sphere-problem.jpg
Thanks for any help.
- Bob
_______________________________________________
Radiance-general mailing list
Radiance-general@radiance-online.org
http://www.radiance-online.org/mailman/listinfo/radiance-general
_______________________________________________
Radiance-general mailing list
Radiance-general@radiance-online.org
http://www.radiance-online.org/mailman/listinfo/radiance-general
Mark is right. To get the correct appearance out of a triangle mesh, you actually need to use a displacement map to give the underlying model the correct appearance w.r.t. grazing shadows such as this one. Implementing displacement maps in a ray tracer is pretty difficult, and in the end it costs more to render them than simply increasing the resolution of your T-mesh as Mark suggests.
-Greg
···
From: Mark Stock <mstock@umich.edu>
Date: December 13, 2005 6:49:52 AM PST
Bob,
Your guess is right. Radiance's triangles, even with normal
interpolation, are still flat. To use the normals to present a true curved surface would (I think) require an implicit representation of the surface.
This particular example, with a low-res mesh and direct sunlight, is the "poster-child" of this problem.
I usually avoid this problem by a combination of higher resolution (I use tri meshes up to 1M elements) and more ambient than direct light.
So, I see no way to completely avoid this for some problems.
Mark
mstock@umich.edu
On Tue, 13 Dec 2005, bob coyne wrote:
Hi,
I'm having a problem rendering polygon mesh objects with interpolated
vertex normals (converted via obj2mesh). I'm running Radiance 3.7.2b
patch release 22 Aug 2005.
When I render a sphere mesh that's illuminated from above and to the
side, I get bad artifacts along the shadow line, with large dark
triangular wedges periodically protruding into the illuminated
area. (See link below for what this looks like.) The dark triangles
seem to correspond to those quadrilaterals in the mesh where only a
single vertex is illuminated. My guess is that it's treating the whole
quad as pointing away from the light source, even though one vertex
and a significant area of it are in the illuminated region of the
object.
Is there any way to avoid this?
www.semanticlight.com/images/sphere-problem.jpg
Thanks for any help.
- Bob
