[ros-users] small text for report which includes object detection

René Ladan r.c.ladan at gmail.com
Tue Jul 13 16:03:16 UTC 2010

Hi Matei,

so the wireframe is only used for display reasons and to store the models
more efficiently in the database. Is the detection then realized by comparing
perceived pointcloud with the pointcloud version of the database models?


2010/7/13 Matei Ciocarlie <matei at willowgarage.com>:
> 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 at 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
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