GIS Library - Ellipse area routines. More...

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

Include dependency graph for area_ellipse.c:

Functions
void	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.

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_ellipse.c.

Function Documentation

◆ G_area_for_zone_on_ellipsoid()

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

north	north coordinate
south	south coordinate

Returns: cell area

Definition at line 89 of file area_ellipse.c.

References G_darea0_on_ellipsoid().

◆ G_begin_zone_area_on_ellipsoid()

void 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

a	semi-major axis
e2	ellipsoid eccentricity
s	scale factor

Definition at line 47 of file area_ellipse.c.

◆ G_darea0_on_ellipsoid()

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

lat latitude

Returns: cell area

Definition at line 63 of file area_ellipse.c.

References Radians, st, and x.

Referenced by G_area_for_zone_on_ellipsoid().

Functions

Detailed Description

Function Documentation

◆ G_area_for_zone_on_ellipsoid()

◆ G_begin_zone_area_on_ellipsoid()

◆ G_darea0_on_ellipsoid()