Cycling 74 » Topic: point clouds

point clouds

Barney Haynes — Sat, 11 Feb 2006 23:23:41 +0000

Greetings,

Has anyone worked with point clouds in open GL? I tried the brute force
method of reading each point into jit.gl.sketch, but it took along
time. The results were a tad sluggish averaging 8 to 9 fps on G5 dual
2.7. Is there is a more efficient way of doing this? If not can anyone
recommend a plug in or application for the mac that will convert point
clouds to obj files? I’ve seen several on line but the cost is
prohibitive enough to preclude experimentation.

Thanks

Barney

Re: point clouds

Wesley Smith — Sat, 11 Feb 2006 23:43:00 +0000

Well, I learned a new term today. I don’t see anyway of efficiently
doing this in jitter right now. I think the best way to go would be
to modify the jit.gl.gridshape SDK example and change the @position
and @scale attributes to matrix inputs for drawing, say, thousands of
spheres per frame. You would pass in 2 3-plane nx1 matrices with
position and scale data and on each render pass, it would call draw
for every scale/position pair, just moving the sphere around.

wes

Re: point clouds

Barney Haynes — Mon, 13 Feb 2006 02:03:02 +0000

Thanks Wes,
Will the jit.gl.gridshape solution run more efficiently on the graphics
card once all the data points are loaded?
Barney

Re: point clouds

Wesley Smith — Mon, 13 Feb 2006 03:23:16 +0000

You know,
I’m not incredibly familiar with the point cloud litterature, so I’m
going to refrain from answering your question as I don’t want to
posture a wild guess. That said, the best thing to do is avoid tons
of max messages. Point clouds seem like an ideal candidate for their
own external as from what cursoiry knowledge I have they require a
decently sophisticated data structure to manage their rendering. From
what I could tell, people were using octrees to choose the detail of
the rendering. If you set this up in a jitter external, you could
have a float parameter for precision that would traverse the octree to
a particular level of detail. This way, you could adjust the detail
to the machine you’re running on and get interactive frame-rates.

Hope this helps. If you’re really into the point cloud thing, I would
take this opportunity to learn how to make a jitter external. Once
you make one successfully, you realize how simple it really is and
your jittering will be that much better since you can overcome hacking
objects together and instead make your own, saving you much processing
power.

good luck,
wes

PS, on yahoo groups, there is a jitter-dev list. you may find the
archives handy when you start out.

Re: point clouds

Barney Haynes — Tue, 14 Feb 2006 00:55:12 +0000

Wes,
Thanks again.
Sounds like my summer vacation plans are starting to become a little
more concrete.
Barney