Python MPA image example

david.moro

Hi, I am working on the integration of a camera on the VOXL2. The camera acts as a USB CDC device and outputs an 8-bit greyscale image on ttyACM0. The manufacturer provides a python example to talk to the camera. I was able to deploy it on the voxl2 and read the images. Now I would like to push those to a pipeline for consumption by voxl-streamer and other processes. Do you have any sample code or guidance on how to do this on python? I would like to have a functional prototype of the whole thing before porting it to C++.

Thanks!

Alex Kushleyev

@david-moro , here is a complete example that receives rtsp stream and publishes images via MPA:

https://gitlab.com/voxl-public/voxl-sdk/utilities/voxl-mpa-tools/-/blob/pympa-experimental/tools/python/rtsp_rx_mpa_pub.py

You need to build voxl-mpa-tools package from this branch and install it on VOXL2. The python scripts will get installed to /usr/share/modalai/voxl-mpa-tools/, you will need at least pympa.py which provides wrappers for python bindings for the mpa functions. libpympa.so will be installed to /usr/lib which contains the C side of the bindings.

Since you don't need opencv, you can just extract the mpa publishing part from the example and add it to your python camera code.

Alex

david.moro

Awesome! Will give it a try. Thanks @Alex-Kushleyev !

david.moro

@Alex-Kushleyev , it worked. Thanks!

Alex Kushleyev

@david-moro , awesome! thanks for confirming.

Alex

Meytal Lempel

@Alex-Kushleyev Hi!

My team and I are working with both voxl1 and voxl2 based platforms. We used your example and changed it to publish a ros topic (Image) to pipe on voxl2. It works great. Now we try to do the same on voxl1 (compiling the same code to ipk) and encounter the problem:

Traceback (most recent call last):
  File "ros_img_mpa_pub.py", line 19, in <module>
    from pympa import *
  File "/usr/share/modalai/voxl-mpa-tools/pympa.py", line 23, in <module>
    pympa = ct.CDLL("libpympa.so")
  File "/usr/lib/python3.6/ctypes/__init__.py", line 348, in __init__
    self._handle = _dlopen(self._name, mode)
OSError: libpympa.so: wrong ELF class: ELFCLASS64

Is there any other branch that may be suitable for voxl1 to our purpose?

Thank you, Meytal

Alex Kushleyev

Hi @Meytal-Lempel ,

There was an issue causing a 64 bit library to be installed into /usr/lib on VOXL1. 32 bit library was never built. I fixed the issue on the pympa branch : https://gitlab.com/voxl-public/voxl-sdk/utilities/voxl-mpa-tools/-/commit/4e9f35ee26217e490c28cf559f4c4b33e0bacd59

Native python3 on VOXL1 is 32 bit.

After building and installing the ipk on voxl1, you can check the library for 32 bit:

readelf -a /usr/lib/libpympa.so | more
ELF Header:
  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF32
  Data:                              2's complement, little endian

The 64-bit libpympa.so library will now go to /usr/lib64, as it should on VOXL1

I hope this helps!

Alex

Meytal Lempel

@Alex-Kushleyev Thank you, it works!