18 #include <grass/gis.h> 
   53     M = s * a * a * M_PI * (1 - e2) / E;
 
   75     return (M * (x / (1.0 - x * x) + 0.5 * 
log((1.0 + x) / (1.0 - x))));
 
double G_area_for_zone_on_ellipsoid(double north, double south)
Calculates area between latitudes. 
 
double G_darea0_on_ellipsoid(double lat)
Calculate integral for area between two latitudes. 
 
int G_begin_zone_area_on_ellipsoid(double a, double e2, double s)
Begin area calculations for ellipsoid.