agpy 0.1 documentation

Source code for agpy.posang

try:
    import coords
except ImportError:
    print "posang requires coords"
from numpy import pi,arctan2,sin,cos,tan

[docs]def posang(l1,b1,l2,b2,system='galactic',units='degrees',**kwargs): """ Return the position angle between two points assuming a rectilinear coordinate system (I think; at the very least I am making no corrections for wcs). INPUT: longitude1, latitude1, longitude2, latitude2 Defaults to GALACTIC coordinates. **kwargs are passed to coords.Position """ pos1 = coords.Position([l1,b1],system=system,**kwargs) ra1,dec1 = pos1.j2000() pos2 = coords.Position([l2,b2],system=system,**kwargs) ra2,dec2 = pos2.j2000() radiff = (ra1-ra2)/180.*pi angle = arctan2( sin(radiff) , cos(dec1*pi/180.)*tan(dec2*pi/180.) - sin(dec1*pi/180.)*cos(radiff) ) if units == 'degrees': return angle/pi*180 elif units == 'radians': return angle else: raise ValueError("Invalid units: %s" % units)