McMillan Airfield GPS origin is not correct

[Jaeyoung-Lim]

When comparing to the map, the origin of the GPS coordinates are not correct and seems to be off a few hundred meters.

I tried fixing this comparing on google maps, but changing
https://github.com/PX4/sitl_gazebo/blob/12da9e6104aaf72a0c52bf802644310f0c5b1ee1/worlds/mcmillan_airfield.world#L18-L23

Didn't have an effect on setting the gps origins. It seems like https://github.com/PX4/sitl_gazebo/blob/master/src/gazebo_gps_plugin.cpp#L51 is not able to be modified.

@ahcorde Is there somewhere else that the world origins are set?

Cross posted from PX4/PX4-SITL_gazebo-classic#496

[issouker97]

Hi , unfortunately i don't have any reply for your question , in the other hand i want to add person_walking i clone it but i don't know how to launch it in gazebo , actually i need the command to launch it , i would be grateful if you could help me

[Jaeyoung-Lim]

@issouker97 I believe your issue is not related to your issue. Please don't hijack the topic of this thread

[Jaeyoung-Lim]

@ahcorde Could you shed any light on this issue?

[ahcorde]

The tags that you mentioned are being readed in the Gazebo code ( in the world class ).

In the plugin you need to setup some env vars:

 // Use environment variables if set for home position.
  const char *env_lat = std::getenv("PX4_HOME_LAT");
  const char *env_lon = std::getenv("PX4_HOME_LON");
  const char *env_alt = std::getenv("PX4_HOME_ALT");

[Jaeyoung-Lim]

@ahcorde Without the environment variables, it reads from the worldfile with https://github.com/PX4/sitl_gazebo/blob/master/src/gazebo_gps_plugin.cpp#L105, However even if I change the spherical coordinates in https://github.com/PX4/sitl_gazebo/blob/master/worlds/mcmillan_airfield.world#L20 the returned value doesn't change

Therefore, the problem is that the return value from

  gazebo::common::SphericalCoordinatesPtr spherical_coords = world->SphericalCoords();

Doesn't seem to reflect the tag properly from the world file.

[Jaeyoung-Lim]

@ahcorde I can confirm that when reading the spherical coordinates from the world object, it returns the origin set from the mcmillan_airfield.tif file and not the one that is defined in the .world file

[Jaeyoung-Lim]

@ahcorde It seems like gazebo overrides the spherical coordinate defined in the world file and uses the origin of the DEM if I understand correctly the following.

If this is the default behavior, this would explain the issues that I have been seeing.

https://github.com/osrf/gazebo/blob/063d7386ed5499c2883de48e19ff5fb9dec01dff/gazebo/physics/HeightmapShape.cc#L109-L131

    // Modify the reference geotedic latitude/longitude.
    // A GPS sensor will use the real georeferenced coordinates of the terrain.
    common::SphericalCoordinatesPtr sphericalCoordinates;
    sphericalCoordinates = this->world->SphericalCoords();

    if (sphericalCoordinates)
    {
      ignition::math::Angle latitude, longitude;
      double elevation;

      this->dem.GetGeoReferenceOrigin(latitude, longitude);
      elevation = this->dem.GetElevation(0.0, 0.0);

      sphericalCoordinates->SetLatitudeReference(latitude);
      sphericalCoordinates->SetLongitudeReference(longitude);
      sphericalCoordinates->SetElevationReference(elevation);
      sphericalCoordinates.reset();
    }
    else
      gzerr << "Unable to get a valid SphericalCoordinates pointer\n";

    return 0;
  }