area_sphere.c File Reference

GIS Library - Sphereical area calculation routines. More...

#include <math.h>
#include <grass/gis.h>
#include "pi.h"

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Functions
void	G_begin_zone_area_on_sphere (double r, double s)
	Initialize calculations for sphere. More...
double	G_darea0_on_sphere (double lat)
	Calculates integral for area between two latitudes. More...
double	G_area_for_zone_on_sphere (double north, double south)
	Calculates area between latitudes. More...

Detailed Description

GIS Library - Sphereical area calculation routines.

(C) 2001-2009 by the GRASS Development Team

This program is free software under the GNU General Public License (>=v2). Read the file COPYING that comes with GRASS for details.

Author

Original author CERL

Definition in file area_sphere.c.

Function Documentation

G_area_for_zone_on_sphere()

double G_area_for_zone_on_sphere	(	double	north,
		double	south
	)

Calculates area between latitudes.

This routine shows how to calculate area between two lats, but isn't efficient for row by row since G_darea0_on_sphere() will be called twice for the same lat, once as a south then again as a north.

Returns the area between latitudes north and south scaled by the factor s passed to G_begin_zone_area_on_sphere().

Parameters

	north
[in]	south

Returns

double

Definition at line 69 of file area_sphere.c.

References G_darea0_on_sphere().

G_begin_zone_area_on_sphere()

void G_begin_zone_area_on_sphere	(	double	r,
		double	s
	)

Initialize calculations for sphere.

Initializes raster area calculations for a sphere. The radius of the sphere is r and s is a scale factor to allow for calculations of a part of the zone (see G_begin_zone_area_on_ellipsoid()).

Parameters

r	radius of sphere
s	scale factor

Definition at line 35 of file area_sphere.c.

G_darea0_on_sphere()

double G_darea0_on_sphere

(

double

lat

)

Calculates integral for area between two latitudes.

Parameters

lat

latitude

Returns

area value

Definition at line 47 of file area_sphere.c.

References Radians, and st.

Referenced by G_area_for_zone_on_sphere().