Hi Rene,

That's generally correct, except for the transformation of the point
cloud into wireframe. The tabletop_object_detector uses sensor data
directly as point clouds. You might see a wireframe displayed on the
screen but that's only after a database model has been recognized. The
wireframe is that of the model, superimposed on the point cloud that
has been recognized.

Matei

On Tue, Jul 13, 2010 at 4:59 AM, René Ladan <r.c.ladan@gmail.com> wrote:
> Hi,
>
> below is a text I intend to include in a report. Do I get the basic ideas right?
>
> Regards,
> Rene
>
> Object handling consists of several steps, which are performed by the
> tabletop_object_detector (and other) nodes.
> •       Get an image of the object (e.g. a pool ball) from e.g. a stereo
> camera with texturing or e.g. a laser range finder.
> •       Transform the image (either a stereo-photo or a “sphere” of
> distances) into a point cloud. A point cloud is a collection of
> points, where all points have a number of pre-defined attributes, like
> spatial coordinates, color, or neighborhood density. Point clouds are
> the universal data structures for performing 3-dimensional algorithms
> within ROS. TODO: figure out the algorithm
> •       Transform the point cloud into a wireframe. TODO: figure out which
> algorithm is used for this.
> •       Now that an approximate wireframe model of the object is available,
> (because the camera images are probably imperfect), this model can be
> compared to a database of existing, perfect wireframe models. Because
> the models are stored as blobs in the database, the approximation is
> done in the ROS node. The database is thus only used a storage
> backend.
> •       The comparison algorithm, given the actual model at one side and the
> database models at the other side, is able to calculate the likelihood
> that the presented object matches a or multiple objects in the
> database (e.g. for a ping-pong ball, it could say “90% pool ball, 8%
> bottle cap, and 2% unknown”).
>
> --
> http://www.rene-ladan.nl/
>
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-- 
Matei Ciocarlie
Research Scientist
Willow Garage Inc.
650-475-9780