Position angle convention

The position angle convention adopted is that the top of the image is defined to be 0 degrees with rotation clockwise considered to be positive.

However, to provide greater flexibility, the packages ELLPRO, ELLFOU and GRAPHS can adopt a user specified convention if you set values for the hidden parameters ANGCON (which defines the direction of rotation in which angle increases) and ANGOFF (which defines the position angle offset) from the command line.