Visual Servoing for Crazyflie drone 2.1+

[yeko31]

Dear ViSP Community,

I'm trying to perform april tag based navigation for the Crazyflie 2.1+ drone. I noticed a similar example was performed for the Parrot Bebop 2 drone. Kindly seeking support to clarify below points.

1. What is the use of the Homogeneous matrix? Is it to convert 3D point into a 2D image plane of the drone?
2. Can we use the Homogeneous matrix for the crazyflie 2.1+ drone? or Is it unique to the parrot bebop 2?
3. In the provided example, does all the processing(calculating velocities) occur on board itself?
4. Are there any drone specific parameters in controller (qe)? Can it be generalizable for any drone?

Hope to have some guidance on performing april tag based navigation, Thank you for your time.
Yehan.

[fspindle]

1. As stated in the doc, an homogeneous matrix a_M_b corresponds to the 3D transformation between two 3D frames (a and b). Given the normalized coordinates of a 3D point in frame b (X, Y, Z, 1) it allows to compute the coordinates of the point in frame a.
2. Homogenous matrix can be used everywhere
3. For the specific example you are pointing, since the Bebop2 doesn't allow access to the onboard processor, the image from the camera is received by a ground station and processed to compute the velocities using a visual vervoing scheme. The velocities are then send back to the bebop. If you have a drone that allows access to the onboard computer, everything can be done onboard.
4. Could be generalized. You have "just" to adjust the position of the camera frame wrt to the frame in which you apply the drone commands (matrix c2_M_e in the example).
5. For Apriltag, just visit vpDetectorAprilTag doc. There are a lot of examples including how to control a robot using a tag as visual feature