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

[Matei Ciocarlie]

Hi Renee,

For now you will have to add models to the database by hand - we will
have some tutorials coming out probably next week on how to do that.

Matei

On Wed, Jul 14, 2010 at 3:14 AM, René Ladan <r.c.ladan at gmail.com> wrote:
> Hi,
>
> is there currently any node available to input custom models?
> The model_assembler node seems to have vanished in thin air.
>
> Regards,
> Rene
>
> 2010/7/13 Matei Ciocarlie <matei at willowgarage.com>:
>> That's hard to quantify precisely... I would say that you should not
>> worry about precision too much, any reasonably lifelike mesh will do.
>>
>> It also depends what else is in the database of models: if you only
>> have your own models, then only those will be fitted against. You will
>> be able to recognize fewer objects, but at least other models will not
>> get in the way. You can also play with the thresholds in
>> tabletop_object_detector/src/tabletop_node.cpp to make the recognition
>> more forgiving.
>>
>> Matei
>>
>> On Tue, Jul 13, 2010 at 9:24 AM, René Ladan <r.c.ladan at gmail.com> wrote:
>>> Hi Matei,
>>>
>>> I get it now ;)
>>>
>>> If I want to model my own objects (for any reason), how precise and
>>> complete must the triangle meshes be for the object detection to work?
>>>
>>> Regards.
>>> Rene
>>>
>>> 2010/7/13 Matei Ciocarlie <matei at willowgarage.com>:
>>>> Hi Rene,
>>>>
>>>> The models are stored in the database as triangle meshes. For display,
>>>> we found it more clear to render them as wireframe rather than
>>>> triangle meshes, as the wireframe still allows the original point
>>>> cloud to show trough a little bit.
>>>>
>>>> The detection is done by comparing the perceived point cloud against
>>>> the triangle mesh stored in the database.
>>>>
>>>> Best,
>>>> Matei
>>>>
>>>> On Tue, Jul 13, 2010 at 9:03 AM, René Ladan <r.c.ladan at gmail.com> wrote:
>>>>> 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?
>>>>>
>>>>> Regards,
>>>>> Rene
>>>>>
>>>>> 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/
>>>>>>>
>>>>>>> GPG fingerprint = E738 5471 D185 7013 0EE0  4FC8 3C1D 6F83 12E1 84F6
>>>>>>> (subkeys.pgp.net)
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>>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Matei Ciocarlie
>>>>>> Research Scientist
>>>>>> Willow Garage Inc.
>>>>>> 650-475-9780
>>>>>> _______________________________________________
>>>>>> ros-users mailing list
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>>>>>>
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>>>>
>>>>
>>>>
>>>> --
>>>> Matei Ciocarlie
>>>> Research Scientist
>>>> Willow Garage Inc.
>>>> 650-475-9780
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>>
>>
>> --
>> Matei Ciocarlie
>> Research Scientist
>> Willow Garage Inc.
>> 650-475-9780
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>> ros-users at code.ros.org
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-- 
Matei Ciocarlie
Research Scientist
Willow Garage Inc.
650-475-9780