Index: /issm/trunk-jpl/src/m/coordsystems/xy2ll.py
===================================================================
--- /issm/trunk-jpl/src/m/coordsystems/xy2ll.py	(revision 15507)
+++ /issm/trunk-jpl/src/m/coordsystems/xy2ll.py	(revision 15507)
@@ -0,0 +1,82 @@
+import numpy as npy
+from math import pi
+
+def xy2ll(x, y, sgn, *args):
+	'''
+	XY2LL - converts xy to lat long
+	
+	Converts Polar  Stereographic (X, Y) coordinates for the polar regions to
+	latitude and longitude Stereographic (X, Y) coordinates for the polar
+	regions.
+	Author: Michael P. Schodlok, December 2003 (map2xy.m)
+	
+	Usage:
+	   [lat, lon] = xy2ll(x, y, sgn);
+	   [lat, lon] = xy2ll(x, y, sgn, central_meridian, standard_parallel);
+	
+	   - sgn = Sign of latitude +1 : north latitude (default is mer=45 lat=70)
+	                            -1 : south latitude (default is mer=0  lat=71)
+	'''
+
+	#Get central_meridian and standard_parallel depending on hemisphere
+	if len(args) == 2:
+		delta = args[0]
+		slat  = args[1]
+	elif len(args) == 0:
+		if sgn == 1:
+			delta = 45 
+			slat = 70
+			print 'Warning: expecting coordinates in polar stereographic (Std Latitude: 70degN Meridian: 45deg)'
+		elif sgn == -1:
+			delta = 0  
+			slat = 71
+			print 'Warning: expecting coordinates in polar stereographic (Std Latitude: 71degS Meridian: 0deg)'
+		else:
+			raise ValueError('sgn should be either +1 or -1')
+	else:
+		raise StandardError('bad usage: type "help(xy2ll)" for details')
+
+	# if x,y passed as lists, convert to numpy arrays
+	if type(x) != "numpy.ndarray":
+		x=npy.array(x)
+	if type(y) != "numpy.ndarray":
+		y=npy.array(y)
+
+	## Conversion constant from degrees to radians
+	cde = 57.29577951
+	## Radius of the earth in meters
+	re = 6378.273*10**3
+	## Eccentricity of the Hughes ellipsoid squared
+	ex2 = .006693883
+	## Eccentricity of the Hughes ellipsoid
+	ex = npy.sqrt(ex2)
+	
+	sl = slat*pi/180.
+	rho = npy.sqrt(x**2 + y**2)
+	cm = npy.cos(sl) / npy.sqrt(1.0 - ex2 * (npy.sin(sl)**2))
+	T = npy.tan((pi/4.0) - (sl/2.0)) / ((1.0 - ex*npy.sin(sl)) / (1.0 + ex*npy.sin(sl)))**(ex / 2.0)
+	
+	if abs(slat-90.) < 1.e-5:
+		T = rho*npy.sqrt((1. + ex)**(1. + ex) * (1. - ex)**(1. - ex)) / 2. / re
+	else:
+		T = rho * T / (re * cm)
+	
+	chi = (pi / 2.0) - 2.0 * npy.arctan(T)
+	lat = chi + ((ex2 / 2.0) + (5.0 * ex2**2.0 / 24.0) + (ex2**3.0 / 12.0)) * \
+		npy.sin(2 * chi) + ((7.0 * ex2**2.0 / 48.0) + (29.0 * ex2**3 / 240.0)) * \
+		npy.sin(4.0 * chi) + (7.0 * ex2**3.0 / 120.0) * npy.sin(6.0 * chi) 
+	
+	lat = sgn * lat
+	lon = npy.arctan2(sgn * x,-sgn * y)
+	lon = sgn * lon
+	
+	res1 = npy.nonzero(rho <= 0.1)
+	if len(res1[0] > 0):
+		lat[res1] = 90. * sgn
+		lon[res1] = 0.0
+	
+	lon = lon * 180. / pi
+	lat = lat * 180. / pi
+	lon = lon - delta 
+
+	return lat, lon