[ros-users] 2d numpy arr msgs?

[Tingfan Wu (UCSD)]

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
>>
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>>
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