18 #include <grass/gis.h> 
   44     return (M = s * 2.0 * r * r * M_PI);
 
double G_darea0_on_sphere(double lat)
Calculates integral for area between two latitudes. 
int G_begin_zone_area_on_sphere(double r, double s)
Initialize calculations for sphere. 
double G_area_for_zone_on_sphere(double north, double south)
Calculates area between latitudes.