[x3d-public] ideal points in IndexedFaceSet

[Leonard Daly]

Hi Andrey,

As I understand your need, you want to put something in essentially the 
backdrop of the scene. This needs to be far enough away that it will 
never have parallax and the user cannot zoom in to anything that might 
be displayed. This would normally be down with the X3D node 
"Background", but that requires six total images, when all that is 
visible is one ("Front") and part of another two ("Up" and "Down"). In 
the case of really wide-angle lenses, there might be portions of "Left" 
and "Right" that show up too.

Would it be possible to construct template images that is lens-dependent 
that marks out the visible areas and those portions of the scene that 
are too far away (10km in your description) just be painted into the 
background image. The "Back" image can always be a transparent PNG as 
would the regions of the other background images that are outside of the 
lens' field-of-view.

Leonard Daly



> We are using x3d models to present long-range 3d scenes captured by a 
> quad stereo camera. And really far objects do not have the distance 
> resolved, so they should be treated as at infinity. We first tried to 
> use background node for such images, but it is not very convenient - 
> we had to provide all 6 images (only one is real), and extend the 
> camera image to match the stereo angle to 1/6 of the full sphere. The 
> rest of the models consist of multiple surfaces as IndexedFaceSet (the 
> viewer is here: https://community.elphel.com/3d+map, just the models: 
> https://community.elphel.com/3d+map/models/). So we ended up with just 
> a very far (at 10,000 m with the rest of the objects closer than 
> 1000m) IndexedFaceSet instead of the background.
>
> Can it make sense to extend IndexedFaceSet (and possibly some other 
> nodes) to use ideal points (x,y,z,0) without increasing number of the 
> point coordinates?
> For our particular application just a single boolean would do, but 
> other applications might benefit from a mixture of the finite and and 
> ideal points by providing a per-vertex boolean array. This can make 
> more uniform representation to replace background and suggest a 
> straightforward way to export the model to the systems that do not 
> support objects at infinity.
>
>
>
>
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-- 
*Leonard Daly*
3D Systems & Cloud Consultant
LA ACM SIGGRAPH Past Chair
President, Daly Realism - /Creating the Future/
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