# Cannot see obstacle\_distance\_fused on QGC **URL:** \ **Category:** PX4 Autopilot\ **Created:** [April 9, 2025, 8:39pm UTC](https://discuss.px4.io/t/cannot-see-obstacle-distance-fused-on-qgc/44936 "2025-04-09T20:39:30Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![aroig1](https://discuss.px4.io/user_avatar/discuss.px4.io/aroig1/32/19077_2.png) [@aroig1](https://discuss.px4.io/u/aroig1)\ **Post date:** [April 9, 2025, 8:39pm UTC](https://discuss.px4.io/t/cannot-see-obstacle-distance-fused-on-qgc/44936/1 "2025-04-09T20:39:30Z")
Hello, I am trying to send obstacle\_distance messages to my Pixhawk6X flight controller from a Nvidia Jetson Orin Nano companion computer connected via ethernet using ROS2 uORB messages. My intention is to then query these messages on my ground control station to display the LiDAR data. However, I am having issues getting PX4 to publish the obstacle\_distance data. I am not able to see the obstacle\_distance topics in the MAVLink Inspector however I am able to see them using the listener command in the MAVLink console. I read that the publish revolved around the obstacle\_distance\_fused message, however when I use the listener with that message it indicates that it is never published. I have tried the steps to activate the collision prevention such as setting CP\_DIST to 1, and modifying the dds\_topics.yaml to include the obstacle\_distance\_fused publication as described in: [https://docs.px4.io/main/en/computer\_vision/collision\_prevention.html](https://collision_prevention) then re-flashed the Pixhawk with the custom firmware, and the result did not change. Note, I pulled the most recent repository changes on the main PX4 branch and was receiving missing parameters errors in QGC after re-flashing. It said I was missing the parameters: BAT1\_V\_LOAD\_DROP, BAT2\_V\_LOAD\_DROP, and COM\_OBS\_AVOID. Is there anything else I should try, or steps that I am missing? Any help would be appreciated. ---
**Author:** ![dakejahl](https://discuss.px4.io/user_avatar/discuss.px4.io/dakejahl/32/20420_2.png) [@dakejahl](https://discuss.px4.io/u/dakejahl)\ **Post date:** [April 10, 2025, 3:22am UTC](https://discuss.px4.io/t/cannot-see-obstacle-distance-fused-on-qgc/44936/2 "2025-04-10T03:22:06Z")
This should be testable in simulation > **[Collision Prevention | PX4 Guide (main)](https://docs.px4.io/main/en/computer_vision/collision_prevention.html)** > > PX4 User and Developer Guide Although I just tried and it doesn’t appear to work. @Claudio-Chies could you take a look? Are the docs missing a step or did maybe something change that broke Collision Prevention? ---
**Author:** ![Claudio-Chies](https://discuss.px4.io/user_avatar/discuss.px4.io/claudio-chies/32/16980_2.png) [@Claudio-Chies](https://discuss.px4.io/u/Claudio-Chies)\ **Post date:** [April 14, 2025, 6:25am UTC](https://discuss.px4.io/t/cannot-see-obstacle-distance-fused-on-qgc/44936/3 "2025-04-14T06:25:48Z")
Collision prevention in SITL, using the lidar airframes doesnt work, or using ros to publish the obstacle\_distance message doesnt work? I can have a look in the next few days ---
**Author:** ![aroig1](https://discuss.px4.io/user_avatar/discuss.px4.io/aroig1/32/19077_2.png) [@aroig1](https://discuss.px4.io/u/aroig1)\ **Post date:** [April 14, 2025, 5:43pm UTC](https://discuss.px4.io/t/cannot-see-obstacle-distance-fused-on-qgc/44936/4 "2025-04-14T17:43:35Z")
For my case, its that I cannot get px4 to publish the obstacle\_distance\_fused message. I am able to get the obstacle\_distance published via a ros2 node on my Nvidia Jetson. If there is an issue with the most recent release causing this, would there be an older release that I could use that we know works? ---
**Author:** ![Claudio-Chies](https://discuss.px4.io/user_avatar/discuss.px4.io/claudio-chies/32/16980_2.png) [@Claudio-Chies](https://discuss.px4.io/u/Claudio-Chies)\ **Post date:** [April 15, 2025, 7:34am UTC](https://discuss.px4.io/t/cannot-see-obstacle-distance-fused-on-qgc/44936/5 "2025-04-15T07:34:05Z")
you should publish only the `obstacle_distance` and not `obstacle_distance_fused`. see [docs](https://docs.px4.io/main/en/computer_vision/collision_prevention.html#companion-computers) The collision prevention in PX4 takes in all different sensors and measurements it has and fuses them into a combined ObstacleDistance message called `obstacle_distance_fused` so if you have a 1d lidar pointing forward, and a companion computer with a 360 lidar publishing into `obstacle_distance` both would be merged into `obstacle_distance_fused`. ---
**Author:** ![aroig1](https://discuss.px4.io/user_avatar/discuss.px4.io/aroig1/32/19077_2.png) [@aroig1](https://discuss.px4.io/u/aroig1)\ **Post date:** [April 15, 2025, 8:04pm UTC](https://discuss.px4.io/t/cannot-see-obstacle-distance-fused-on-qgc/44936/6 "2025-04-15T20:04:13Z")
Yes I understand that aspect. My companion computer (Nvidia Jetson Orin Nano) is publishing the obstacle\_distance topics as you described. The issue is that I am not seeing them on the MAVLink inspector within QGC. I saw on another discussion that it being displayed is directly associated with the obstacle\_distance\_fused message functionality, but when using the MAVLink console and doing “listener obstacle\_distance\_fused”, it says that it is never published. The reason I need it to be published by PX4 is that I am trying to query and display that data via a MavLink command on my own Ground Control Station, and as of now am receiving no obstacle\_distance messages when listening with MAVLink. ---
**Author:** ![aroig1](https://discuss.px4.io/user_avatar/discuss.px4.io/aroig1/32/19077_2.png) [@aroig1](https://discuss.px4.io/u/aroig1)\ **Post date:** [April 21, 2025, 7:10pm UTC](https://discuss.px4.io/t/cannot-see-obstacle-distance-fused-on-qgc/44936/7 "2025-04-21T19:10:00Z")
@dakejahl Do you know what the last release was that the Collision Prevention still worked? ---
**Author:** ![dakejahl](https://discuss.px4.io/user_avatar/discuss.px4.io/dakejahl/32/20420_2.png) [@dakejahl](https://discuss.px4.io/u/dakejahl)\ **Post date:** [April 21, 2025, 7:21pm UTC](https://discuss.px4.io/t/cannot-see-obstacle-distance-fused-on-qgc/44936/8 "2025-04-21T19:21:43Z")
I don’t know. Hey @Claudio-Chies just a heads up Collision Prevention is currently broken. I tested with SITL using the 2D lidar model same as before, but no worky now. If you have some time maybe you could take a look? Thanks 😁 ---
**Author:** ![Claudio-Chies](https://discuss.px4.io/user_avatar/discuss.px4.io/claudio-chies/32/16980_2.png) [@Claudio-Chies](https://discuss.px4.io/u/Claudio-Chies)\ **Post date:** [June 18, 2025, 7:21am UTC](https://discuss.px4.io/t/cannot-see-obstacle-distance-fused-on-qgc/44936/9 "2025-06-18T07:21:26Z")
might have the time to look into it in the next few weeks, no promises. issue will be tracked here > > > \### Describe the bug > > Some users have reported issues with the new collision pre…vention. We should regression test the implementation since a lot of changes have been made even since the original PR. > > @PX4/testflights ---
**Author:** ![system](https://discuss.px4.io/uploads/default/original/3X/7/3/73ce918bdcd64854de904f0c8d9ab70ca9723f2a.png) [@system](https://discuss.px4.io/u/system)\ **Post date:** [September 16, 2025, 7:21am UTC](https://discuss.px4.io/t/cannot-see-obstacle-distance-fused-on-qgc/44936/10 "2025-09-16T07:21:33Z")
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