Two MAVLink (type 10) rangefinders with the same orientation

clyde · August 22, 2023, 10:29pm

We have an ROV with 2 down-facing rangefinders (Ping1D, A50 DVL). The plan was to set them both up as MAVLink rangefinders, but when I read the ArduSub code I don’t see any code that looks at DISTANCE_SENSOR.id to disambiguate by id. So, it seems that 2 MAVLink rangefinders with the same orientation will stomp on each other.

github.com

ArduPilot/ardupilot/blob/5ddb649ed1a6d1eb23dd731ec74710e7f1609b5a/libraries/AP_RangeFinder/AP_RangeFinder_MAVLink.cpp#L25


      
          
          #include "AP_RangeFinder_MAVLink.h"
          
          #if AP_RANGEFINDER_MAVLINK_ENABLED
          
          #include <AP_HAL/AP_HAL.h>
          
          /*
             Set the distance based on a MAVLINK message
          */
          void AP_RangeFinder_MAVLink::handle_msg(const mavlink_message_t &msg)
          {
              mavlink_distance_sensor_t packet;
              mavlink_msg_distance_sensor_decode(&msg, &packet);
          
              // only accept distances for the configured orentation
              if (packet.orientation == orientation()) {
                  state.last_reading_ms = AP_HAL::millis();
                  distance_cm = packet.current_distance;
                  _max_distance_cm = packet.max_distance;
                  _min_distance_cm = packet.min_distance;

I can think of various workarounds, but all of them involve code changes somewhere. Am I reading this correctly?

Thanks,
/Clyde

EliotBR · August 31, 2023, 6:51am

Hi @clyde,

Yes, as far as I can tell ArduPilot does not differentiate between rangefinder instances.

In Sub-4.1 it seems there’s even a restriction to only accept downward distances.

If they’re close enough in values this could be fine, but I agree it’s sub-optimal if there’s disagreement and you want to be able to differentiate between them to know which one to trust from a consistency metric or something.

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Two MAVLink (type 10) rangefinders with the same orientation

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