GRASS GIS 7 Programmer's Manual  7.5.svn(2017)-r71915
rhumbline.c File Reference

GIS Library - Rhumbline calculation routines. More...

`#include <math.h>`
`#include <grass/gis.h>`
`#include "pi.h"`
Include dependency graph for rhumbline.c:

Go to the source code of this file.

## Functions

int G_begin_rhumbline_equation (double lon1, double lat1, double lon2, double lat2)
Start rhumbline calculations. More...

double G_rhumbline_lat_from_lon (double lon)
Calculates rhumbline latitude. More...

## Detailed Description

GIS Library - Rhumbline calculation routines.

From "Map Projections" by Peter Richardus and Ron K. Alder, 1972
(526.8 R39m in Map & Geography Library)
Page 20,21, formulas 2.21, 2.22

Formula is the equation of a rhumbline from (lat1,lon1) to (lat2,lon2). Input is lon, output is lat (all in degrees).

Note: Formula only works if 0 < abs(lon2-lon1) < 180. If lon1 == lon2 then rhumbline is the merdian lon1 (and the formula will fail).
WARNING: This code is preliminary. It may not even be correct.

(C) 2001-2014 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.

Date
1999-2014

Definition in file rhumbline.c.

## Function Documentation

 int G_begin_rhumbline_equation ( double lon1, double lat1, double lon2, double lat2 )

Start rhumbline calculations.

Note: This function must be called before other rhumbline functions to initialize parameters.

Parameters
 [in] lon1,lat1 longitude, latitude of first point [in] lon2,lat2 longitude, latitude of second point
Returns
1 on success
0 on error

Definition at line 60 of file rhumbline.c.

 double G_rhumbline_lat_from_lon ( double lon )

Calculates rhumbline latitude.

Note: Function only works if lon1 < lon < lon2.

Parameters
 [in] lon longitude
Returns
double latitude in degrees

Definition at line 100 of file rhumbline.c.