[x3d-public] Allowing Normal node to accompany PointSet, then achieving well-defined rendering

[Don Brutzman]

On 12/5/2019 7:01 AM, Andreas Plesch wrote:
> Hi Michalis,
> 
> thanks for thinking this through.

yes

> To me, then, there are really two options concerning normal maps for Pointset:
> 
> (A) allow normal maps for Pointsets, and introduce a MFVec3f Tangent
> and probably Bitangent nodes, similar to the existing Normal node.
> Similar to the Normal node, values would be automatically computed for
> continuous surfaces using the MIKKTspace method when not provided.
> (B) If introducing Tangent nodes is not feasible at this point, do not
> allow normal maps for Pointsets and rely exclusively on the Normal
> node to provide normals, per vertex.

hmmm, aren't tangents unambiguously computable from surface geometry and Normal vectors?  Knowing the surrounding mesh geometry constrains the more-general case of a point.

If they are computable (tangent, bitangent, whatever) and accurately renderable only when another property or two is specified, then such properties might be included in PointProperties (i.e. tangent=true/false).

If tangent/bitangent remain geometrically unconstrained, then let us defer solving that new feature until we can address it more thoroughly.

The primary motivation is to keep simple consistent data structures associated with Coordinate data.  This would allow PointSet to have compatible scene-graph structures as IndexedLineSet, IndexedFaceSet etc.

Similarly important motivation is that scanning companies often include Normal data together with their mesh (or point cloud) outputs.

So it would seem there is no impediment to including Normal with PointSet in X3Dv4.  Adding corresponding prose for rendering can follow, with tangent definitions a candidate future capability to consider.

all the best, Don
-- 
Don Brutzman  Naval Postgraduate School, Code USW/Br       brutzman at nps.edu
Watkins 270,  MOVES Institute, Monterey CA 93943-5000 USA   +1.831.656.2149
X3D graphics, virtual worlds, navy robotics http://faculty.nps.edu/brutzman