area_ellipse.c File Reference

GIS Library - Ellipse area routines. More...

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

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Functions
int	G_begin_zone_area_on_ellipsoid (double a, double e2, double s)
	Begin area calculations for ellipsoid. More...
double	G_darea0_on_ellipsoid (double lat)
	Calculate integral for area between two latitudes. More...
double	G_area_for_zone_on_ellipsoid (double north, double south)
	Calculates area between latitudes. More...

Detailed Description

GIS Library - Ellipse area routines.

(C) 2001-2008 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

GRASS GIS Development Team

Date

1999-2008

Definition in file area_ellipse.c.

Function Documentation

double G_area_for_zone_on_ellipsoid	(	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_ellipsoid() 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_ellipsoid().

Parameters

[in]	north
[in]	south

Returns

double

Definition at line 96 of file area_ellipse.c.

References G_darea0_on_ellipsoid().

int G_begin_zone_area_on_ellipsoid	(	double	a,
		double	e2,
		double	s
	)

Begin area calculations for ellipsoid.

Initializes raster area calculations for an ellipsoid, where a is the semi-major axis of the ellipse (in meters), e2 is the ellipsoid eccentricity squared, and s is a scale factor to allow for calculations of part of the zone (s=1.0 is full zone, s=0.5 is half the zone, and s=360/ew_res is for a single grid cell).
Note: e2 must be positive. A negative value makes no sense, and zero implies a sphere.

Parameters

[in]	a	semi-major axis
[in]	e2	ellipsoid eccentricity
[in]	s	scale factor

Returns

always returns 0

Definition at line 50 of file area_ellipse.c.

Referenced by G_begin_cell_area_calculations().

double G_darea0_on_ellipsoid

(

double

lat

)

Calculate integral for area between two latitudes.

This routine is part of the integral for the area between two latitudes.

Parameters

[in]

lat

Returns

double

Definition at line 69 of file area_ellipse.c.

References wxnviz::log, and Radians.

Referenced by G_area_for_zone_on_ellipsoid(), and G_begin_cell_area_calculations().