[x3d-public] Normal vectors for points and lines?

[vmarchetti at kshell.com]

A contrary issues is that we haven't identified the visualization role of normal direction for a point cloud. That direction data is generated by  scanning processes and  it is used in some surface reconstruction algorithms that generate a mesh from point cloud data; however at this stage of the technology that surface reconstruction is not explicitly referenced in the X3D standard. For visualizatione there are two suggestions for use of normal data that have no relation to each other:

One is the 'point cloud with hair' idea as shown in the DirectedPointSet example on the page http://kshell.com/pages/archimedes/visualization_comparison/ <http://kshell.com/pages/archimedes/visualization_comparison/> . This rendering is done with an X3D Prototype (see http://kshell.com/pages/archimedes/visualization_comparison/pointset_archie_dps.x3d ) that does contain a Coordinate node and a Normal node; but to define the visualization it also requires two Appearance fields and an SFFLoat field.

The other idea is to use the Normal field to cull the point cloud, to not show points which are directed away from the viewpoint. The result should be kind of a quasi-mesh visualization, visually intermediate between a point cloud and a surface mesh constructed from the cloud. This use of the normal field is analogous to the use of the Normal node in the TriangleSet and FaceSet nodes, where the normal direction is not directly represented but only indirectly shown, where the surface is shaded so that it visually appears to be perpendicular to the normal vectors.

I don't think we information as to which of these visualizations would be more useful to the user community. So as a standards writing matter, what guidance can we offer to the browser implementers as to how to use the normal data for a PointSet when implementing this extension in X3D V4?

The same considerations would hold for adding a 'normal' field to the LineSet nodes.

Vince Marchetti




> On Nov 28, 2019, at 1:31 PM, Don Brutzman <brutzman at nps.edu> wrote:
> 
> It would seem that we are going to allow Normal nodes in PointSet nodes - not sure if consensus was declared on that yet.  Any contrary issues will be good to know.
> 
> For example: X3dMeshDesignPattern.x3d
> https://x3dgraphics.com/examples/X3dForAdvancedModeling/Scanning/X3dMeshDesignPatternIndex.html
> 
> Wondering, will we allow Normal nodes within LineSet and IndexedLineSet also?  (They are defined in the example also.)
> 
> Of note is that X_ITE renders scene in the preceding page correctly, no complaints about Normal nodes.
> 
> Seems logical to consistently allow Normal with all such geometry nodes, preserving data-structure patterns also helps preserve data.
> 
> IF that is agreeable then I will update DOCTYPE x3d-4.0.dtd and schema x3d-4.0.xsd and X3DUOM accordingly.
> How to render lines with normals would then seem to be another capability to integrate in revised rendering definitions of the X3Dv4 specification.
> 
> 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
> 
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