# mpa to ros voxl-tag detector

Source: https://forum.modalai.com/topic/1296/mpa-to-ros-voxl-tag-detector
Category: Flight Core and Legacy VOXL (https://forum.modalai.com/category/9/flight-core-and-legacy-voxl)
Tags: voxl
Posted: 2022-09-06 04:11:24 UTC by Mostafa Nikpour
Replies: 6 · Views: 1775

## Mostafa Nikpour · 2022-09-06 04:11:24 UTC

Hi,

I am trying to get voxl-tag detector data by tracking camera in host PC, but it gives me some weird numbers that are not related to tag detection data. I use the  roslaunch voxl_mpa_to_ros voxl_mpa_to_ros.launch in voxl and rostopic echo /tracking_tag_overlay in PC.![Screenshot from 2022-09-06 16-06-03.png](https://forum.modalai.com/assets/uploads/files/1662437418039-screenshot-from-2022-09-06-16-06-03.png)

## Reply by Guest · 2022-09-07 22:37:30 UTC

Hi,

You're echoing the tracking tag **overlay**, which is an image stream with the original image annotated with any detected tags, not a ros packet with information about the tags. You'll want to view this with rviz or rqt_image_view.

## Reply by Mostafa Nikpour · 2022-09-08 02:13:32 UTC

Hi Alex,

How can I remotely access the data displayed by  `voxl-inspect-tags`? I noticed that there were several ROS topics available:
```
/imu0
/imu1
/qvio_overlay
/rosout
/rosout_agg
/stereo_tag_overlay/left
/stereo_tag_overlay/right
/tracking
/tracking_tag_overlay
/voa_pc_out
```
but none of those (`tracking` and `tracking_tag_overlay`) seem to be what I need.

## Reply by Nicolas Brissonneau · 2022-09-13 16:57:15 UTC

Hi,

I'm also interested in accessing this data, I noticed the voxl-inspect-tags code manages to access it but I'm not sure what is the proper approach to send it through MAVROS/Mavlink to an external flight controller. I tried the following things:

* adding the libraries from voxl-inspect-tags that open the pipe associated with tags to a CMakeLists file in a ROS package, though it doesn't compile with an error message stating they're incompatible when running catkin_make

* reading the "/tracking" ROS msg from within the kinetic docker and then:
 (1) use a standard ROS package for AprilTag detection, doesn't work as it requires catkin build which fails.
 (2) catkin_make a ROS package for AprilTag detection, but I didn't have any luck with compiling OpenCV in the docker.

My ultimate goal would be to send this data to PX4 via UART for precision landing but so far I'm a bit lost and would truly appreciate an opinion on this. Would it be simpler to copy the process from voxl-inspect-tags and use mavlink directly to send it to the separate flight controller? If so how would one add mavlink messaging capabilities to the .c code? Or am I way off?

## Reply by Patrick Hinchey · 2022-11-16 07:11:24 UTC

Did anything come of this?
I'm also trying to access AprilTag location in ROS, but there's nothing obvious in ```rostopic list```.
I can't find any documentation on it either.
@modaltb

## Reply by Patrick Hinchey · 2022-11-17 15:34:08 UTC (in reply to Guest)

@Alex-Gardner Is there any way to get the tag X.Y.Z coords in ROS?

## Reply by Jose Alfredo Rosas Cordova · 2023-02-15 17:51:54 UTC (in reply to Nicolas Brissonneau)

Hello, @Nicolas-Brissonneau:

I am trying to do the same thing as you and am stuck with the same problem. Did you manage to solve it?