Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
# algorithm courtesy of Simon Tatham (`Railway problem',
# pers.comm. to ijackson@chiark 23.1.2004)
railway_angleoffset = atan2(*q_plane[0:2])
- railway_theta = atan2(*dp_plane[0:2]) - railway_angleoffset
- railway_phi = atan2(*dq_plane[0:2]) - railway_angleoffset
+ # these two angles are unconventional: clockwise from north
+ railway_theta = tau/4 - (atan2(*dp_plane[0:2]) - railway_angleoffset)
+ railway_phi = tau/4 - (atan2(*dq_plane[0:2]) - railway_angleoffset)
railway_cos_theta = cos(railway_theta)
railway_cos_phi = cos(railway_phi)