[ros-users] PR-2 Camera frames

[Patrick Doyle]

On Mon, Oct 25, 2010 at 7:41 PM, Tully Foote <tfoote at willowgarage.com> wrote:
> Bharath,
> All frames are positions in free space in meters.  The camera frames point x
> forward, and the frames with optical in them are z forward.  These
> conventions are defined in REP 103 http://www.ros.org/reps/rep-0103.html
>
Having just looked through a bunch of URDF, I had a somewhat similar
question -- when I see link with a name such as
r_forearm_cam_optical_frame, to what does the origin of that link
refer?  Is it the location of the camera itself, or is it the focal
point of the camera?  (Not that I'm terribly sure what I would do with
the knowledge of the focal point in 3D space, although I suppose it
would be useful if I wanted to know the optimum position for holding
something up to the camera).

And diverging somewhat, to what point in space does the origin of
something like the r_gripper_l_finger_tip_frame refer?  Is it the
center of the finger tips?  Is it the portion of the finger tip
closest to the robot?  Is it the portion of the finger tip furthest
from the robot?  (I begin to see why biologists and doctors use words
like "proximal" and "distal" in this context.)

--wpd