The command is sent by a dedicated mavlink command and forwarded to the fixed wing position controller.
The pattern is defined by the radius of the major axis, the radius of the minor axis and the orientation. The pattern is then defined by:
The upper part of the pattern consist of a clockwise circle with radius defined by the minor axis. The center of the circle is defined by the major axis minus the minor axis away from the pattern center.
The lower part of the pattern consist of a counter-clockwise circle with the same definitions as above.
In between, the circles are connected with straight lines in a cross configuration. The lines are always tangetial to the circles.
The orientation rotates the major axis around the NED down axis.
The loitering logic is defined inside its own class used by the fixed wing position control module. It defines which segment (one of the circles or lines) is active and uses the path controller (npfg or l1-control) to determine the desired roll angle.
A feedback mavlink message is send with the executed pattern parameters.
Konrad