Index: /issm/trunk-jpl/src/m/lambert/lambert2xy.m
===================================================================
--- /issm/trunk-jpl/src/m/lambert/lambert2xy.m	(revision 15125)
+++ /issm/trunk-jpl/src/m/lambert/lambert2xy.m	(revision 15126)
@@ -1,3 +1,3 @@
-function [x,y] = lambert2xy(lat,lon,projection_center_lat,projection_center_lon)  
+function [x,y] = lambert2xy(lat,lon,sgn,projection_center_lat,projection_center_lon)  
 %LAMBERT2XY - converts lat long from Lambert Azimuthal to Polar Stereographic
 %
@@ -7,23 +7,25 @@
 %
 %   Usage:
-%      [x,y] = ll2xy(lat,lon)
-%      [x,y] = ll2xy(lat,lon,projection_center_lat,projection_center_lon)
+%      [x,y] = lambert2xy(lat,lon,sgn)
+%      [x,y] = lambert2xy(lat,lon,sgn,projection_center_lat,projection_center_lon)
 %
 %      - provide lat in [-90,90] and lon in [-180,180].
-%
-%      - default: North hemisphere [projection center lat = 90 lon=0]
-%                 South hemisphere [projection center lat = -90 lon=0]
+
+%      - sgn = +1 N hemisphere [default projection center lat = 90 lon=0]
+%              -1 S hemisphere [default projection center lat = -90 lon=0]
 
 %Get projection_center_lat and projection_center_lon 
-if nargin==4,
+if nargin==5,
 	latitude0  = projection_center_lat;
 	longitude0 = projection_center_lon;
-elseif nargin==2,
-	if lat>0,
+elseif nargin==3,
+	if sgn==1,
 		latitude0 = 90; longitude0 = 0;
 		disp('Info: creating coordinates in polar stereographic (Projection center lat: 90N lon: 0)');
-	elseif lat<0,
+	elseif sgn==-1,
 		latitude0 = -90; longitude0 = 0;
 		disp('Info: creating coordinates in polar stereographic (Projection center lat: 90S lon: 0)');
+	else
+		error('Sign should be either +1 or -1');
 	end
 else
@@ -58,14 +60,10 @@
 
 % Calculation of x and y
-if(lat==90)
-	rho=a*sqrt(qp-q);
-	x=rho*sin(lam-lam0);
-	y=-rho*cos(lam-lam0);
-elseif(lat==-90)
-	rho=a*sqrt(qp+q);
-	x=rho*sin(lam-lam0);
-	y=rho*cos(lam-lam0);
+if(abs(lat)==90)
+	x=0.0; 
+	y=0.0; 
 else
 	x=(B*D)*(cos(b)*sin(lam-lam0));
 	y=(B/D)*((cos(b0)*sin(b))-(sin(b0)*cos(b)*cos(lam-lam0)));
 end
+
Index: /issm/trunk-jpl/src/m/lambert/xy2lambert.m
===================================================================
--- /issm/trunk-jpl/src/m/lambert/xy2lambert.m	(revision 15126)
+++ /issm/trunk-jpl/src/m/lambert/xy2lambert.m	(revision 15126)
@@ -0,0 +1,69 @@
+function [lat,lon] = xy2lambert(x,y,sgn,projection_center_lat,projection_center_lon)  
+%XY2LAMBERT - converts xy to lat lon in Lambert Azimuthal
+%
+%   Converts from Ploar Stereographic (X,Y) coordinates to geodetic 
+%   lat lon that are in Lambert Azimuthal (equal area) projection.
+%
+%   Usage:
+%      [lat,lon] = xy2lambert(x,y,sgn)
+%      [lat,lon] = xy2lambert(x,y,sgn,projection_center_lat,projection_center_lon)
+%
+%      - provide lat in [-90,90] and lon in [-180,180].
+%
+%      - sgn = +1 N hemisphere [default projection center lat = 90 lon=0]
+%              -1 S hemisphere [default projection center lat = -90 lon=0]
+
+%Get projection_center_lat and projection_center_lon 
+if nargin==5,
+	latitude0  = projection_center_lat;
+	longitude0 = projection_center_lon;
+elseif nargin==3,
+	if sgn==1,
+		latitude0 = 90; longitude0 = 0;
+		disp('Info: creating coordinates in Lambert Azimuthal equal-area (Projection center lat: 90N lon: 0)');
+	elseif sgn==-1,
+		latitude0 = -90; longitude0 = 0;
+		disp('Info: creating coordinates in Lambert Azimuthal equal-area (Projection center lat: 90S lon: 0)');
+	else
+		error('Sign should be either +1 or -1');
+	end
+else
+	help xy2lambert
+	error('bad usage');
+end
+
+% Radius of the earth in meters 
+a = 6378137.0;
+% Eccentricity of the Hughes ellipsoid squared
+e = 0.081819191;
+
+% Projection center latitude and longitude in radians 
+phi0 = latitude0 * pi/180; 
+lam0 = longitude0 * pi/180; 
+
+% Some constants based on phi0 and lam0
+% (as in forward calculation)
+qp= (1-e^2)*((1/(1-e^2))-((1/(2*e))*log((1-e)/(1+e))));
+q0=(1-e^2)*((sin(phi0)/(1-e^2*sin(phi0)*sin(phi0)))-((1/(2*e))*log((1-e*sin(phi0))/(1+e*sin(phi0)))));
+Rq=a*sqrt(qp/2);
+b0=asin(q0/qp);
+D =a*(cos(phi0)/sqrt(1-e^2*sin(phi0)*sin(phi0)))/(Rq*cos(b0));
+
+% Some other (x,y) dependent parameters 
+rho=sqrt((x/D)^2+(D*y)^2);
+C=2*asin(rho/(2*Rq));
+b_prime=asin((cos(C)*sin(b0))+((D*y*sin(C)*cos(b0))/rho));
+
+% Calculation of lat and lon 
+dist=sqrt(x^2+y^2);
+if(dist<=0.1)
+	lat=sgn*90.0;
+	lon=0.0;
+else
+	lat_rad=b_prime+((e^2/3+31*e^4/180+517*e^6/5040)*sin(2*b_prime))+((23*e^4/360+251*e^6/3780)*sin(4*b_prime))+((761*e^6/45360)*sin(6*b_prime));
+	lon_rad=lam0+atan(x*sin(C)/(D*rho*cos(b0)*cos(C)-D^2*y*sin(b0)*sin(C)));
+	% in degrees 
+	lat=lat_rad*180/pi;
+	lon=lon_rad*180/pi;
+end
+