area_poly1.c File Reference

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

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

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Macros
#define	TWOPI   M_PI + M_PI

Functions
int	G_begin_ellipsoid_polygon_area (double a, double e2)
	Begin area calculations.
double	G_ellipsoid_polygon_area (const double *lon, const double *lat, int n)
	Area of lat-long polygon.

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Detailed Description

GIS Library - Polygon area calculation 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_poly1.c.

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Macro Definition Documentation

#define TWOPI   M_PI + M_PI

Definition at line 22 of file area_poly1.c.

Referenced by G_ellipsoid_polygon_area().

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Function Documentation

int G_begin_ellipsoid_polygon_area	(	double	a,
		double	e2
	)

Begin area calculations.

This initializes the polygon area calculations for the ellipsoid with semi-major axis a (in meters) and ellipsoid eccentricity squared e2.

Parameters:

[in]	a	semi-major axis
[in]	e2	ellipsoid eccentricity

Returns:

always returns 0

Definition at line 67 of file area_poly1.c.

Referenced by G_begin_polygon_area_calculations().

double G_ellipsoid_polygon_area	(	const double *	lon,
		const double *	lat,
		int	n
	)

Area of lat-long polygon.

Returns the area in square meters of the polygon described by the n pairs of lat,long vertices for latitude-longitude grids.
Note: This routine assumes grid lines on the connecting the vertices (as opposed to geodesics).

Parameters:

[in]	lon	array of longitudes
[in]	lat	array of latitudes
[in]	n	number of lat,lon pairs

Returns:

double Area in square meters

Definition at line 110 of file area_poly1.c.

References Radians, and TWOPI.

Referenced by G_area_of_polygon().