Perhaps the biggest challenge in underwater robotics is localization:
- radio signals (e.g., GPS) are absorbed rapidly in water, particularly seawater
- you often can't see the seafloor
- sonar is useful, but it is typically big, expensive and power-hungry (although this is improving)
- inexpensive IMUs aren't good for more than a few meters, and the good ones are big and expensive
Orca3 supports two SLAM (Simultaneous Localization And Mapping) systems:
- fiducial_vlam looks for ArUco markers in the environment using the forward-facing camera. This is useful for test environments like pools.
- orb_slam2_ros looks for ORB features along the seafloor. It is configured to use a custom down-facing stereo camera. This works well in simulation, but it has not been tested in the field.
The FiducialLocalizer node does the following:
- subscribe to
/fiducial_observations(a list of marker observations) and/forward_camera/camera_pose(the pose of the camera generated by solvePnP or GTSAM) - reject poses generated by markers that are too far away (~2m). This avoids unstable solutions.
- calculate the map->base_link transform
- publish the map->odom transform
No transforms are published until a marker is observed. After the first observation transforms are published at the target rate with updated timestamps, even if they are old.
| Parameter | Type | Default | Notes |
|---|---|---|---|
| map_frame_id | string | map | Map frame id |
| odom_frame_id | string | odom | Odom frame id |
| camera_frame_id | string | camera_frame | Camera frame id |
| publish_rate | int | 20 | How often to publish transforms, Hz |
| wait_for_transform_ms | int | 500 | How long to wait for the odom->base transform, ms |
| transform_expiration_ms | int | 1000 | How far ahead to post-date the map->odom transform, ms |
| good_pose_distance | double | 2.0 | Maximum distance for a good marker observation, m |
The OrbSlam2Localizer node does the following:
- subscribe to
/camera_pose - calculate the map->base_link transform
- publish the map->odom transform
The systems starts as soon as there's a good pose. The simulated world has a depth of 4m and the mapping starts immediately.
| Parameter | Type | Default | Notes |
|---|---|---|---|
| map_frame_id | string | map | Map frame id |
| odom_frame_id | string | odom | Odom frame id |
| camera_frame_id | string | camera_frame | Camera frame id |
| publish_rate | int | 20 | How often to publish transforms, Hz |
| transform_expiration_ms | int | 1000 | How far ahead to post-date the map->odom transform, ms |