ROS Coordinate Systems
Refer to ROS standard https://www.ros.org/reps/rep-0103.html:
- For positions represented with reference to a initial body frame, FLU (NWU) should be used
- However, if the position represents a geographic location (either global or local), ENU should be used
- This includes
/mavros/local_position, outputing ENU frame Code
- This includes
Similarly, in RVIS visualisations, RGB represents the 3-axis of the coordinates in sequence. The default global coordinates is map. This map should represent ENU aligned global position or ENU aligned local position.
warning
Reading from this issue, we should note that NWU is neither a ROS standard nor a Mavros convention, when describing a location.
However, NWU is used in sensors for example IMU for their linear acceleration and angular rates, which creates confusion, by Mavros. (Mavlink always uses NED)
Frame ID and Coordinate Frames#
Naming convention: REP 105
Rule of thumb: sensor data should be in NED frame (depth, VIO), global position and orientation should be in ENU frame (Motion Capture, Code).
From Mavros to ROS (Planning)#
| Frame ID | Coordinate Frame | Remark | Example |
|---|---|---|---|
map | ENU | True North Aligned | /mavros/local_position/pose (configurable in launch file) |
map_ned | NED | By Mavros | |
base_link | local ENU | INCONSISTENT | /mavros/local_position/odom, and static tf sent by mavros |
base_link_frd | local NED | By Mavros | Should use this as the pointcloud measurement frame |
base_link_enu | shall we define this? |
It appears that although ROS recommand NWU as the convention for local frame, but base_link in mavros uses ENU.
From Mavros to ROS (VIO)#
| Frame ID | Coordinate Frame | Remark | Example |
|---|---|---|---|
base_link | ENU | /mavros/imu/data/orientation | |
base_link | local NWU | /mavros/imu/data/angular_velocity, /mavros/imu/data/linear_acceleration | |
base_link | local NWU | INCONSISTENT | /mavros/imu/data_raw/* |
From ROS to Mavros (VIO)#
| Frame ID | Coordinate Frame | Remark | Example |
|---|---|---|---|
odom | ENU | True North Aligned | |
odome_ned | NED | By Mavros | /mavros/odometry/out with frame_id = "odom_ned" |
// Publish helper TFs used for frame transformation in the odometry plugin std::vector<geometry_msgs::TransformStamped> transform_vector; add_static_transform("map", "map_ned", Eigen::Affine3d(ftf::quaternion_from_rpy(M_PI, 0, M_PI_2)),transform_vector); add_static_transform("odom", "odom_ned", Eigen::Affine3d(ftf::quaternion_from_rpy(M_PI, 0, M_PI_2)),transform_vector); add_static_transform("base_link", "base_link_frd", Eigen::Affine3d(ftf::quaternion_from_rpy(M_PI, 0, 0)),transform_vector);
tf2_static_broadcaster.sendTransform(transform_vector);Case Study /mavros/local_position#
All message below assumes map as the frame id, and the child frame id is base_link. This means that map is representing ENU coordinates.
Also, the orientation is also converted to ENU frame, which means base_link is also in ENU frame.
tf#
The tf transformation is optionally sent by setting the parameter local_position/tf/send to true, located at px4_config.yaml