gis/distance.c File Reference

GIS Library - Distance calculation functions. More...

#include <math.h>
#include <grass/gis.h>
#include <grass/glocale.h>

Include dependency graph for gis/distance.c:

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Functions
int	G_begin_distance_calculations (void)
	Begin distance calculations. More...
double	G_distance (double e1, double n1, double e2, double n2)
	Returns distance in meters. More...
double	G_distance_between_line_segments (double ax1, double ay1, double ax2, double ay2, double bx1, double by1, double bx2, double by2)
	Returns distance between two line segments in meters. More...
double	G_distance_point_to_line_segment (double xp, double yp, double x1, double y1, double x2, double y2)
	Returns distance between a point and line segment in meters. More...

Detailed Description

GIS Library - Distance calculation functions.

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

(C) 2001-2009, 2011 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 gis/distance.c.

Function Documentation

G_begin_distance_calculations()

int G_begin_distance_calculations

(

void

)

Begin distance calculations.

Initializes the distance calculations. It is used both for the planimetric and latitude-longitude projections.

Returns

0 if projection has no metrix (ie. imagery)

1 if projection is planimetric

2 if projection is latitude-longitude

Definition at line 42 of file gis/distance.c.

Referenced by Vect_line_geodesic_distance().

G_distance()

double G_distance	(	double	e1,
		double	n1,
		double	e2,
		double	n2
	)

Returns distance in meters.

This routine computes the distance, in meters, from x1,y1 to x2,y2. If the projection is latitude-longitude, this distance is measured along the geodesic. Two routines perform geodesic distance calculations.

Parameters

e1,n1	east-north coordinates of first point
e2,n2	east-north coordinates of second point

Returns

distance

Definition at line 75 of file gis/distance.c.

References G_geodesic_distance(), PROJECTION_LL, and st.

Referenced by Vect_line_geodesic_distance().

G_distance_between_line_segments()

double G_distance_between_line_segments	(	double	ax1,
		double	ay1,
		double	ax2,
		double	ay2,
		double	bx1,
		double	by1,
		double	bx2,
		double	by2
	)

Returns distance between two line segments in meters.

Parameters

ax1,ay1,ax2,ay2	first segment
bx1,by1,bx2,by2	second segment

Returns

distance value

Definition at line 91 of file gis/distance.c.

References G_intersect_line_segments(), and x.

G_distance_point_to_line_segment()

double G_distance_point_to_line_segment	(	double	xp,
		double	yp,
		double	x1,
		double	y1,
		double	x2,
		double	y2
	)

Returns distance between a point and line segment in meters.

Parameters

xp,yp	point coordinates
x1,y1	segment point coordinates
x2,y2	segment point coordinates

Returns

distance

Definition at line 117 of file gis/distance.c.