I am trying to use atan2 to calculate the angle between two points. With atan2, angles increase counterclockwise, and zero is to the right i.e. The angle originates at positive x, increases up into positive y, swinging round to 180 degrees.
I am using a coordinate system where the "up" axis is actually negative, so values decrease going up the y axis instead of increase. Additionally my x-axis could flip where the right becomes negative.
Is there any easy way to account for my non-standard axis, either in the angle output or to standardise the coordinates before I call atan2?