[x3d-public] ideal points in IndexedFaceSet

GPU Group gpugroup at gmail.com
Fri Feb 16 12:42:04 PST 2018

I've never tried it - using a homogenous coordinate with w = 0.- is that
what you mean?
After projection, don't we divide by w? ie x=x/w, y=y/w. Somewhere. Does
the shader do that automatically? Isn't dividing by zero a problem?
But if it works, then I think you would start by designing a new node type
- CoordinateH node lets say- derived from X3DCoordinateNode, and it would
have MFVec4f point field.
Then web3d browsers internally would need to check if its a CoordinateH
node and if so do a bit different math.
Not sure what the math would be or where it would take place.
How do you do it?
I would love to have one of those quad cameras. I come from photogrammetry
and machine vision, and want to get back into it this year. If I find an
application that pays.

On Fri, Feb 16, 2018 at 12:44 PM, Andrey Filippov <andrey at elphel.com> wrote:

> 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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