The purpose of this practical is to understand the various reference frames used to orient and control the UAV and practice transforming information between these frames. The major takeaways are:
The most common reference frames we will use are the North-East-Down (NED), East-North-Up (ENU), Body, Camera, and sometimes ARTag Marker frames.
The same vector can be expressed in difference reference frames
There are multiple ways in which we can express the difference between two reference frames including euler angles (yaw, pitch, roll), rotation matrices, and quaternions
tf_staticROS topics are a useful way of communicating reference frame information on the Aero Compute Board, but we won’t make immediate use of it, yet.
/mavros/local_position/velocitytopics provide the estimated pose and velocity of the UAV’s body frame with respect to the world frame (i.e. NED or ENU)
Coordinate Frame Practice
We’ve pushed a jupyter notebook exercise to the
laboratory repository that will help us start practicing/learning these concepts and conventions.
At this point you should be able to
git pull upstream master in your
laboratory repo and then navigate to
laboratory/kinematics_dynamics/coordinate_transforms.ipynb. Open this notebook and work through the questions (we’ll try to do this together during class)
PX4 Documentation: https://dev.px4.io/en/ros/external_position_estimation.html