Dear Raphael,

if I were you I'd have a look at this tutorial:
http://www.ros.org/wiki/image_geometry/Tutorials/ProjectTfFrameToImage
and then try to inverse it using
http://www.ros.org/doc/api/image_geometry/html/c++/classimage__geometry_1_1PinholeCameraModel.html#a96e992cd1a511680b8588e81c52b2c27

cheers, D.

On Wed, Jun 9, 2010 at 5:56 PM, zizi poil
<zizipoil.leroidesbois@gmail.com> wrote:
> Dear all,
>
> I am trying to build a node that would reproduce the basics of the camera
> pluggin of rviz.
> The difference is that I'd like to be able to correlate a point clicked by
> the user on the camera screen (in pixels)  with a point from a 3D point
> cloud (in meters).
>
> In other words, I have my stereo camera that generates a 3D point cloud and
> I would like to allow the user to select on of these 3D points using the 2D
> image of the left or right eye.
> If the user clicks a point were no 3d info is available, then I'd like to
> choose the closest 3d point available.
>
> So, I need a way to correlate x,y coordinates in pixels with x,y,z
> coordinates in meters.
>
> I am thinking of 2 main alternatives:
>
> A) project the 3d-points back to a stereo_sensor frame that would represent
> the sensor of the camera, and from there convert my meters in pixels (I know
> 1 pixel is 6 um on my sensor)
> B) send a ray from my pixel point and see if I collide into a 3d point (I
> have no idea how to do this, maybe bullet apparently?)
>
> I have the feeling tf can help me for the first alternative.
> Still, would anyone know precisely how to achieve this and which packages
> would help in this way (ROS is really wide and I am new to it).
> Also, am I taking the good approach or is there a far more simple way do
> this?
>
> Thanks for your help
>
> Raphael
>
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>
>



-- 
MSc. Dejan Pangercic
PhD Student/Researcher
Intelligent Autonomous Systems Group
Technische Universität München
Telephone: +49 (89) 289-26908
E-Mail: dejan.pangercic@cs.tum.edu
WWW: http://ias.cs.tum.edu/people/pangercic