ac_request("geometry_calc_2d","get_line_angle_relative_to_center",double l1sX, double l1sY,double l1eX,double l1eY, double &resAngleInRad);


Here:

l1sX,l1sY,l1eX, l1eY - coordinates of the start and end points of the segment.

The angle of inclination in radians is returned in resAngleInRad.