orca_localize

Orca3 Localization

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.

FiducialLocalizer

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.

Parameters

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

OrbSlam2Localizer

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.

Parameters

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