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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

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
asemi-major axis in meters
e2ellipsoid eccentricity

Definition at line 50 of file geodist.c.

Referenced by G_begin_distance_calculations().

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,lat1longitude,latitude of first point
lon2,lat2longitude,latitude of second point
Returns
distance in meters

Definition at line 196 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(), and Vect_line_geodesic_length().

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
lon1first longitude
lon2second longitude
Returns
double distance in meters

Definition at line 121 of file geodist.c.

References M_PI, Radians, t, and x.

Referenced by G_geodesic_distance().

void G_set_geodesic_distance_lat1 ( double  lat1)

Sets geodesic distance lat1.

Set the first latitude.

Note: Must be called first.

Parameters
lat1first latitude
Returns

Definition at line 69 of file geodist.c.

References Radians.

Referenced by G_geodesic_distance().

void G_set_geodesic_distance_lat2 ( double  lat2)

Sets geodesic distance lat2.

Set the second latitude.

Note: Must be called second.

Parameters
lat2second latitidue

Definition at line 83 of file geodist.c.

References Radians.

Referenced by G_geodesic_distance().