# I can't see OBSTACLE_DISTANCE on QGC

Source: https://forum.modalai.com/topic/3133/i-can-t-see-obstacle_distance-on-qgc
Category: General Questions (https://forum.modalai.com/category/2/general-questions)
Posted: 2024-02-21 11:19:24 UTC by rogerli
Replies: 17 · Views: 3950

## rogerli · 2024-02-21 11:19:24 UTC

I am attempting to use VOXL2 to connect to an external flight controller for collision prevention. I can see the information from voa_pc_out on VOXL2, but I am unable to see the information from OBSTACLE_DISTANCE on QGC. VOXL2 is connected to the telemetry 2 port of the external flight controller via UART. Here are my MAVLink parameter settings:
MAV_1_CONFIG : TELEM 2
MAV_1_FLOW_CTRL : Auto-detected
MAV_1_FORWARD : Disabled
MAV_1_MODE : Onboard
MAV_1_RADIO_CTL : Enabled
MAV_1_RATE : 0
SER_TEL2_BAUD : 921600
COM_OBS_AVOID : Enabled

On the VOXL2, it is connected to the USB/UART add-on board at J3, and the parameters in the voxl-mavlink-server.conf file are set as follows:
{
	"primary_static_gcs_ip":	"192.168.8.10",
	"secondary_static_gcs_ip":	"192.168.124.197",
	"onboard_port_to_autopilot":	14556,
	"onboard_port_from_autopilot":	14557,
	"gcs_port_to_autopilot":	14558,
	"gcs_port_from_autopilot":	14559,
	"en_external_uart_ap":	true,
	"autopilot_uart_bus":	1,
	"autopilot_uart_baudrate":	921600,
	"en_external_ap_timesync":	1,
	"en_external_ap_heartbeat":	1,
	"udp_mtu":	0,
	"gcs_timeout_s":	4.5
}

Then, when I use the "mavlink status" command on QGC to check, I see that the rx loss is 63.1%, why is this problem happening? How can I resolve it?"

## Reply by Moderator (ModalAI staff) · 2024-02-21 16:44:12 UTC

Have you verified the voltage level of your UART match?

## Reply by rogerli · 2024-02-21 20:04:12 UTC (in reply to Moderator)

@Moderator 
The external flight controller I am using is Cube Orange+. The voltage level of UART on both the USB/UART add-on board at J3 and the Cube Orange+ telemetry port (telem2) is shown in the image below
add-on board:
![add-on.jpg](https://forum.modalai.com/assets/uploads/files/1708545557827-add-on.jpg) 
cube orange+:
![cube orange+.jpg](https://forum.modalai.com/assets/uploads/files/1708545560578-cube-orange.jpg)

## Reply by Vinny (ModalAI staff) · 2024-02-22 20:53:00 UTC (in reply to rogerli)

Hi @rogerli 
Are you only connecting the UART and GND?
You need a 2-2, 3-3, and 4-6 cable.
Not sure what the CUBE connector is, but maybe our https://docs.modalai.com/cable-datasheets/#mcbl-00067 will work for you?

Be sure the 3.3V and 5V is not connected.
Hope this helps.

## Reply by wilkinsaf · 2024-02-23 15:17:45 UTC

Shot in the dark I would turn off MAV_1_FORWARD  if it is enabled. 

Also, do you have any other mavlink based device that is connected? If so I would unplug it to see if this helps resolve the issue

## Reply by rogerli · 2024-02-25 18:44:32 UTC

I only connected UART and GND, and VOXL2 is only connected to the Cube Orange+, a WiFi dongle, and a stereo camera.

I can use the "listener obstacle_distance" command on QGC's MAVLink console to obtain depth information about obstacles, and I have successfully enabled collision prevention for the drone in position mode. However, I still cannot see "obstacle_distance" on the MAVLink inspector.

![2c10b38d-a06e-4e0d-8bc5-4d6d04c8faaa-voxl_distance.png](https://forum.modalai.com/assets/uploads/files/1708886588436-2c10b38d-a06e-4e0d-8bc5-4d6d04c8faaa-voxl_distance.png)

## Reply by Eric Katzfey (ModalAI staff) · 2024-02-26 16:59:41 UTC (in reply to rogerli)

@rogerli What messages do you see in mavlink inspector?

## Reply by rogerli · 2024-03-11 08:05:45 UTC (in reply to Eric Katzfey)

@Eric-Katzfey said in [I can't see OBSTACLE\_DISTANCE on QGC](/post/14917):
> mavlink inspector

This is the messages I see in the MAVLink inspector.
![6c9c15c5-c926-4f17-a250-dd14b791311d-Screenshot from 2024-03-11 16-01-00.png](https://forum.modalai.com/assets/uploads/files/1710144256129-6c9c15c5-c926-4f17-a250-dd14b791311d-screenshot-from-2024-03-11-16-01-00.png) 
![43a275aa-2cbc-49ff-b687-3e9a2869ff94-Screenshot from 2024-03-11 16-01-42.png](https://forum.modalai.com/assets/uploads/files/1710144264271-43a275aa-2cbc-49ff-b687-3e9a2869ff94-screenshot-from-2024-03-11-16-01-42.png)

## Reply by Eric Katzfey (ModalAI staff) · 2024-03-12 02:20:02 UTC (in reply to rogerli)

@rogerli The OBSTACLE_DISTANCE Mavlink message is based on the `obstacle_distance_fused` topic. Can you do listener on that topic to see if it is being published?

## Reply by rogerli · 2024-03-18 03:51:52 UTC (in reply to Eric Katzfey)

@Eric-Katzfey said in [I can't see OBSTACLE\_DISTANCE on QGC](/post/15230):

No, I am unable to use the listener command to see the obstacle_distance_fused message. How can I enable this feature?

## Reply by Eric Katzfey (ModalAI staff) · 2024-03-18 15:55:00 UTC (in reply to rogerli)

@rogerli What is the parameter CP_DIST set to?

## Reply by Inverse AJ · 2025-04-03 02:21:59 UTC (in reply to Eric Katzfey)

@Eric-Katzfey I am having a similar problem, where I can see obstacle_distance, but not obstacle_distance_fused using the listener command. When I checked CP_DIST it was set to -1 so I set it to 1 and then I could briefly see both with the listener command, and was able to see obstacle_distance using the mavlink inspector. After unplugging then replugging in my pixhawk, this was gone and I was back to only being able to see obstacle_distance with the listener command. Was there something that could've changed during my restart? I checked CP_DIST and it was still set to 1 even afterwards.

The only notable differences between my system and the original users is that my connection is across ethernet.

## Reply by Eric Katzfey (ModalAI staff) · 2025-04-03 17:02:39 UTC (in reply to Inverse AJ)

@Inverse-AJ A quick look at the code shows that CP_DIST has to be greater than 0 and current flight mode has to be manual position mode. What flight mode are you in?

## Reply by Inverse AJ · 2025-04-08 01:29:19 UTC (in reply to Eric Katzfey)

@Eric-Katzfey I was previously in "Hold" mode, but I tried in "manual" and still am not seeing the obstacle_distance_fused message. I noticed one other difference in my parameters which is that COM_OBS_AVOID doesn't exist for me. 

Another question, I had previously re-flashed the Pixhawk firmware after changing the file: "PX4Autopilot/src/modules/uxrce_dds_client/dds_topics.yaml". I had added the following to the publications section:
- topic: /fmu/out/obstacle_distance_fused
    type: px4_msgs::msg::ObstacleDistance

However, it had no effect so I reverted back to the default px4 firmware shown on QGC. Is that change necessary to see the message or should I leave the default?

## Reply by Inverse AJ · 2025-04-08 02:22:37 UTC (in reply to Eric Katzfey)

@Eric-Katzfey Small update. I also tried it with the custom firmware with that additional publication added (from previous reply), and the result has not changed. obstacle_distance_fused still shows up as "never published" when using the listener. However, with the custom firmware I get warnings from QGC about missing parameters: BAT1_V_LOAD_DROP, BAT2_V_LOAD_DROP, and COM_OBS_AVOID. I pulled the most recent main branch for the PX4 Repository to build it, so maybe there's not support by QGC yet?

## Reply by Eric Katzfey (ModalAI staff) · 2025-04-08 15:49:03 UTC (in reply to Inverse AJ)

@Inverse-AJ Have you asked this question on PX4 forum? https://discuss.px4.io/c/px4/25

## Reply by Inverse AJ · 2025-04-09 20:42:06 UTC (in reply to Eric Katzfey)

@Eric-Katzfey I had not since this discussion was the closest I could find to my issue. But I have created one now: [Cannot see obstacle_distance_fused on QGC](https://discuss.px4.io/t/cannot-see-obstacle-distance-fused-on-qgc/44936)

## Reply by constantines · 2025-07-21 09:09:14 UTC (in reply to Inverse AJ)

@Inverse-AJ @rogerli 
Hi, I also struggled with the *OBSTACLE_DISTANCE* MAVLink message not appearing in the MAVLink Inspector. Moreover, obstacle avoidance was not functioning after I upgraded  v1.3.5 to ModalAI SDK v1.5.0. If you're experiencing this issue, ensure the following:

**Set** *MPC_POS_MODE* to **0** (Simple Position Control) **or 3** (Smooth Position Control). The default value (4, Acceleration-based Input) is incompatible with ModalAI’s VOXL platform.
**Set** *COM_OBS_AVOID* to **1**. This enables obstacle avoidance in PX4.
**Set** *CP_DIST* to a value **greater than 0**. This specifies the critical distance for collision prevention.
**Ensure your drone has a valid home position or local position from QVIO**. This is required for proper navigation.
**Ensure your drone is in Position Hold mode.** Obstacle avoidance requires this flight mode.

Although the *OBSTACLE_DISTANCE* message does not appear in the MAVLink Inspector, QGroundControl displays the obstacle distance overlay in its telemetry view, and the drone successfully performs obstacle avoidance. Note: This applies to ModalAI SDK v1.5.0; check for updates in newer versions.

![f0d0fe9f-61ff-4287-9210-186dafc0879a-Untitled.jpg](https://forum.modalai.com/assets/uploads/files/1753088579973-f0d0fe9f-61ff-4287-9210-186dafc0879a-untitled.jpg)