geodist.c File Reference

GIS Library - Geodesic distance routines. More...

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

Include dependency graph for geodist.c:

Go to the source code of this file.

Functions
void	G_begin_geodesic_distance (double a, double e2)
	Begin geodesic distance. More...
void	G_set_geodesic_distance_lat1 (double lat1)
	Sets geodesic distance lat1. More...
void	G_set_geodesic_distance_lat2 (double lat2)
	Sets geodesic distance lat2. More...
double	G_geodesic_distance_lon_to_lon (double lon1, double lon2)
	Calculates geodesic distance. More...
double	G_geodesic_distance (double lon1, double lat1, double lon2, double lat2)
	Calculates geodesic distance. More...

Detailed Description

GIS Library - Geodesic distance routines.

Distance from point to point along a geodesic code from Paul D. Thomas, 1970 "Spheroidal Geodesics, Reference Systems, and Local Geometry" U.S. Naval Oceanographic Office, p. 162 Engineering Library 526.3 T36s http://stinet.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=AD0703541

WARNING: this code is preliminary and may be changed, including calling sequences to any of the functions defined here.

(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 geodist.c.

Function Documentation

G_begin_geodesic_distance()

void 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.

Note: Must be called once to establish the ellipsoid.

Parameters

a	semi-major axis in meters
e2	ellipsoid eccentricity

Definition at line 50 of file geodist.c.

G_geodesic_distance()

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

Calculates geodesic distance.

Calculates the geodesic distance from lon1,lat1 to lon2,lat2 in meters.

Note: The calculation of the geodesic distance is fairly costly.

Parameters

lon1,lat1	longitude,latitude of first point
lon2,lat2	longitude,latitude of second point

Returns

distance in meters

Definition at line 195 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().

G_geodesic_distance_lon_to_lon()

double G_geodesic_distance_lon_to_lon	(	double	lon1,
		double	lon2
	)

Calculates 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	first longitude
lon2	second longitude

Returns

double distance in meters

Definition at line 121 of file geodist.c.

Referenced by G_geodesic_distance().

G_set_geodesic_distance_lat1()

void G_set_geodesic_distance_lat1

(

double

lat1

)

Sets geodesic distance lat1.

Set the first latitude.

Note: Must be called first.

Parameters

lat1	first latitude

Returns

Definition at line 69 of file geodist.c.

References Radians, and st.

Referenced by G_geodesic_distance().

G_set_geodesic_distance_lat2()

void G_set_geodesic_distance_lat2

(

double

lat2

)

Sets geodesic distance lat2.

Set the second latitude.

Note: Must be called second.

Parameters

lat2	second latitidue

Definition at line 83 of file geodist.c.

References Radians, and st.

Referenced by G_geodesic_distance().