[Radiance-general] Radiance animation questions

[Georg Mischler]

Zack Rogers wrote:

> [about inter-polygon smoothing]
> I'm guessing that I can not just apply it to my polygons in my radout rad
> file cause there are no normals...but can't the normal be determined
> fairly easily as the cross product of this sides of the polygon?  Do you
> really need to define each surface normal when the surface vertices are
> defined?  Is it just a more expensive calculation?


Unfortunately, a typical rad file is just a heap of unrelated
triangles. Or worse, other types of polygons, which you then need
to split into triangles first.

If the normal vectors aren't supplied, then you'll have to try
to reconstruct the topology of the surface. Basically you run
through the list of triangles multiple times, searching all the
ones that share vertices. The assumption being that the normal of
each vertex will be the average of all adjoining triangles.
As long as the geometry is topologically simple (no manifolds or
intersections etc.), this can be done, but it isn't very
efficient, and may produce unexpected results in some cases.

If your surface has any discontinuities (eg. edges: triangles
connecting at an angle that shouldn't be smoothed away), then
you need to start guessing threshold angles, which is at best
unreliable. If the normals are supplied, then you can just smooth
each triangle individually, and not worry about connections
because you *know* the result will be correct in any case.

In your animation, the most obvious places where I noticed any
lack of smoothness in supposedly curved surfaces were the
handrails, and possibly the roof of the entrance pavillion. Those
effects *won't* go away with normal vector interpolation, because
it's not primarily the shading that gives them away, but the
segmented outlines. You'll have to make shorter segments for that
to improve. For some entity types (extruded arcs and arc segments
in polylines), you can reduce the angle and distance tolerances
in Radout to improve their appearance.


-schorsch

-- 
Georg Mischler  --  simulations developer  --  schorsch at schorsch com
+schorsch.com+  --  lighting design tools  --  http://www.schorsch.com/