[ros-users] 2d numpy arr msgs?

[Tingfan Wu (UCSD)]

bugfix: I forget to specify the numpy.dtype, so you'll get wrong result.
New file attached.

When testing, you should see identical send/recv'd numpy arrays.

$./numpy_nd_msg.py
sending
[[ 0.66123694 -0.49842736  0.52398044]
 [-0.58045769 -0.2468847  -0.96691573]]
I heard
[[ 0.66123694 -0.49842736  0.52398044]
 [-0.58045769 -0.2468847  -0.96691573]]
...

-Tingfan
PhD Student
Machine Perception Laboratory
UC San Diego






On Mon, Aug 22, 2011 at 11:15 AM, Tingfan Wu (UCSD) <t3wu at ucsd.edu> wrote:
> Thanks Ken for the suggestion.
> I made a custom message type generator similar to rospy/numpy_msg.py
> called numpy_nd_msg.py in the attachment. Hopefully it will be useful.
>
> When running as an standalone script, it is a self-talking node
> publishing and subscribing /mytopic with random 2x3 numpy arrays as
> type Float32MultiArray.
>
> To test (some sense of) compatibility, one can run the following
> command to bounce the message
> rostopic echo /mytopic | rostopic pub /mytopic  std_msgs/Float32MultiArray
>
> -Tingfan
> PhD Student
> Machine Perception Laboratory
> UC San Diego
>
>
>
>
>
>
> On Mon, Aug 22, 2011 at 9:29 AM, Ken Conley <kwc at willowgarage.com> wrote:
>> Hi Tingfan,
>>
>> rospy allows you to substitute  your own message
>> serializer/deserializers as you please.  The proposal you suggest
>> would require custom messages as the generators have no knowledge of
>> MultiArrayLayouts.
>>
>> cheers,
>> Ken
>>
>> On Mon, Aug 22, 2011 at 9:09 AM, Tingfan Wu (UCSD) <t3wu at ucsd.edu> wrote:
>>> Hi,
>>> Sorry for replying an old message. But I am also interested in
>>> multidimensional numpy array msg.
>>> My proposal is to initialize the layout of a *MultiArray msg from the
>>> incoming numpy.ndarray information.
>>>
>>> Take Float32MultiArray for an example, the current method of
>>> numpy_serialization in Float32MultiArray.numpy_serialization leaves
>>> the layout untouched. And in the numpy_msg tutorial, the layout seems
>>> to be None through out the example, which seems awkward. Therefore, I
>>> propose to initialize the layout size and stride using the buff when
>>> layout is None. This can be done with a numpy specific __init__() or
>>> just add few lines into numpy_serialization()). Similarly, in the
>>> Float32MultiArray.numpy_deserialization, reshape the array according
>>> to the layout information.
>>>
>>> This shouldn't break cross-language compatibility  as the lowlevel
>>> data is still transferred using the "tostring()" mechanism as 1D
>>> arrays but makes the numpy users' life much easier.
>>>
>>>
>>> -Tingfan
>>> PhD Student
>>> Machine Perception Laboratory
>>> UC San Diego
>>>
>>>
>>>
>>>
>>>
>>>
>>> On Mon, Jun 14, 2010 at 3:27 PM, Ken Conley <kwc at willowgarage.com> wrote:
>>>> The ROS msg IDL only supports 1D arrays. The reshape approach is the correct
>>>> approach to ensure compatibility in multiple languages.
>>>>
>>>>  - Ken
>>>>
>>>> On Mon, Jun 14, 2010 at 3:23 PM, Floris van Breugel <florisvb at gmail.com>
>>>> wrote:
>>>>>
>>>>> Hi folks,
>>>>>
>>>>> Is there a way to publish 2D numpy arrays as messages (using python)? I
>>>>> went through the numpy tutorial for rospy but it seems to only work for 1D
>>>>> arrays. I suppose one could reshape the 2D array to be 1D, and pass the
>>>>> shape as another message, and then reconstruct it on the other side, but
>>>>> maybe there's a more efficient way to do it? Or that functionality could be
>>>>> added to numpy_msg.py?
>>>>> http://www.ros.org/wiki/rospy_tutorials/Tutorials/numpy
>>>>>
>>>>> Thanks!
>>>>>
>>>>> - Floris
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Floris van Breugel
>>>>> Caltech Graduate Student
>>>>> Control and Dynamical Systems
>>>>> (925) 963 8280
>>>>>
>>>>> Wildlife and Landscape Photographer
>>>>> Galleries: http://www.ArtInNaturePhotography.com/
>>>>> Blog: http://www.ArtInNaturePhotography.com/wordpress/
>>>>> 2010 CALENDARS! Now available on my website!
>>>>>
>>>>>
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>>>>
>>>>
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