[ros-users] 2d numpy arr msgs?

Tingfan Wu (UCSD) t3wu at ucsd.edu
Mon Aug 22 16:09:30 UTC 2011

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.

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
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