# Collision Prevention

Source: https://forum.modalai.com/topic/382/collision-prevention
Category: General Questions (https://forum.modalai.com/category/2/general-questions)
Posted: 2021-08-04 20:58:06 UTC by gauravshukla914
Replies: 13 · Views: 2520

## gauravshukla914 · 2021-08-04 20:58:06 UTC

Hi. I'm using a Voxl flight deck with the System Image 3.2.0 / voxl-suite 0.3.4. I want to test collision prevention on this, however I see that this image doesn't support collision prevention. 
Is there any update on this? What are my options? Since I want to enable this feature on my drone for further development.

## Reply by Guest · 2021-08-04 21:25:40 UTC

System image 3.3.0 / Voxl-suite 0.4.6 supports collision prevention using stereo cameras (voxl-dfs-server) and the en_voa flag in /etc/modalai/voxl-vision-px4.conf

## Reply by gauravshukla914 · 2021-08-05 17:10:59 UTC

@Alex-Gardner Thanks for the reply. I updated the image to 3.3.0. I've also set the en_voa flag to true in the configuration file. However when I do the "voxl-vision-px4 -s" to print the obstacle date, I get nothing. 
On checking the services running by voxl-inspect-services, I see that the voxl-dfs -server is enabled but not running. Is there anything else that I need to do?
Also, I'm able to see the stereo camera output in the rqt image viewer.

## Reply by gauravshukla914 · 2021-08-05 19:49:28 UTC

@Alex-Gardner Also, just to let you know, we have the stereo camera replaced, so we have attempted the stereo calibration once. And we pushed the files to VOXL. 
When I do on - voxl-dfs-server I get this
 voxl-dfs-server 
=================================================================
skip_n_frames:                    5
n_disparity_levels:               48
=================================================================
Failed to open calibration file: /data/modalai/opencv_stereo_intrinsics.yml

But the calibaration method that we performed pushes left.yaml and right.yaml files. Is there anything wrong that I'm doing?

## Reply by gauravshukla914 · 2021-08-05 21:42:22 UTC

Update - we were able to push the opencv_intrinsics.yml. But when I do voxl-inspect-services, it still shows dfs server enabled, but not running.

## Reply by gauravshukla914 · 2021-08-06 15:08:19 UTC

Update - we are able to get the obstacle data printed on the terminal. But this only comes when we run the voxl-dfs-server in one terminal and then run voxl-vision-px4 -s in other terminal.
Do we have to always run voxl-dfs-server in one window for this?

## Reply by Guest · 2021-08-06 15:32:01 UTC

voxl-dfs-server and voxl-vision-px4 should run in the background just fine if they're marked as enabled in voxl-inspect-services. If you boot the voxl and see that dfs server is enabled but not running, then can you paste the output of ```journalctl -u voxl-dfs-server``` so we can see why it's aborting

## Reply by gauravshukla914 · 2021-08-06 16:23:45 UTC

@Alex-Gardner its now perfectly running on boot up. Thanks for the help.

## Reply by gauravshukla914 · 2021-08-09 17:32:33 UTC

@Alex-Gardner I want to check the stereo disparity. However, when I do the voxl streamer -c dfs-server, the stream is getting stuck on the the VLC media player. How do I see the disparity output?

## Reply by Guest · 2021-08-09 20:06:29 UTC

The config option is ```dfs-disparity``` not dfs-server

## Reply by Daniel Ryu · 2021-08-24 22:23:15 UTC (in reply to Guest)

@Alex-Gardner Different guy, but I followed the same steps as above and am also just getting a black screen on the VLC player for 
```
voxl-streamer -c dfs-disparity
```

Everything else seems to be working fine when I run voxl-inspect-services (you can see my status here https://forum.modalai.com/topic/409/obstacle_detection-messages-not-appearing/3). 
 
I would like to have collision avoidance integrated onto my drone for a time sensitive project, but the documentation for voxl-dfs-server is not yet present and I am out of resources to turn to.

## Reply by Prasad Antervedi · 2021-10-01 20:32:24 UTC (in reply to gauravshukla914)

@gauravshukla914 Hi! I am also getting the same error (i.e. "Failed to open calibration file: /data/modalai/opencv_stereo_intrinsics.yml" ). How did you manage to get the opencv_stereo_intrinsics.yml file. Did you write it yourself? 
Thanks in advance :D

## Reply by gauravshukla914 · 2021-10-06 16:15:19 UTC

@Prasad-Antervedi as far as I rember we calibrated the stereo cameras and then pushed the resulting files into voxl.

## Reply by Daniel Ryu · 2021-10-06 18:53:14 UTC (in reply to Prasad Antervedi)

@Prasad-Antervedi Try following these: https://docs.modalai.com/calibrate-cameras/