geodist.c File Reference

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

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Functions
int	G_begin_geodesic_distance (double a, double e2)
	begin geodesic distance
int	G_set_geodesic_distance_lat1 (double lat1)
	set geodesic distance lat1
int	G_set_geodesic_distance_lat2 (double lat2)
	set geodesic distance lat2
double	G_geodesic_distance_lon_to_lon (double lon1, double lon2)
	geodesic distance
double	G_geodesic_distance (double lon1, double lat1, double lon2, double lat2)
	geodesic distance

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Function Documentation

int G_begin_geodesic_distance	(	double	a,
		double	e2
	)

begin geodesic distance

Initializes the distance calculations for the ellipsoid with semi-major axis a (in meters) and ellipsoid eccentricity squared e2. It is used only for the latitude-longitude projection.

Parameters:

	a
	e2

Returns:

int

Definition at line 37 of file geodist.c.

References sqrt().

Referenced by G_begin_distance_calculations().

double G_geodesic_distance	(	double	lon1,
		double	lat1,
		double	lon2,
		double	lat2
	)

geodesic distance

Calculates the geodesic distance from lon1,lat1 to lon2,lat2 in meters. The calculation of the geodesic distance is fairly costly. These next three routines provide a mechanism for calculating distance with two fixed latitudes and varying longitude separation.

Parameters:

	lon1
	lat1
	lon2
	lat2

Returns:

double

Definition at line 202 of file geodist.c.

References G_geodesic_distance_lon_to_lon(), G_set_geodesic_distance_lat1(), and G_set_geodesic_distance_lat2().

Referenced by G_distance().

double G_geodesic_distance_lon_to_lon	(	double	lon1,
		double	lon2
	)

geodesic distance

Calculates the geodesic distance from lon1,lat1 to lon2,lat2 in meters, where lat1 was the latitude passed to G_set_geodesic_distance_latl and lat2 was the latitude passed to G_set_geodesic_distance_lat2.

Parameters:

	lon1
	lon2

Returns:

double

Definition at line 119 of file geodist.c.

References PI, Radians, sin(), and sqrt().

Referenced by G_geodesic_distance().

int G_set_geodesic_distance_lat1

(

double

lat1

)

set geodesic distance lat1

Set the first latitude.

Parameters:

lat1

Returns:

int

Definition at line 60 of file geodist.c.

References atan(), Radians, and tan().

Referenced by G_geodesic_distance().

int G_set_geodesic_distance_lat2

(

double

lat2

)

set geodesic distance lat2

Set the second latitude.

Parameters:

lat2

Returns:

int

Definition at line 77 of file geodist.c.

References atan(), cos(), Radians, sin(), and tan().

Referenced by G_geodesic_distance().

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