[Proj] geod C library?

[Evan Miller]

Thanks for the ideas. I ended up using libproject:

http://home.comcast.net/~gevenden56/proj/

The geodesic functions are not very well documented, but code like
this did the trick for a distance calculation:

	#import <project.h>

	/* WGS84 */
	PROJ_ELLIPS E;
	E.a = 6378137.0;
	E.f = 1/298.257223563;
	E.es = (2 - E.f) * E.f;
	E.one_es = 1 - E.es;
	
	PROJ_PT_LPH src_pt, dst_pt;
	src_pt.h = 0.0;
	dst_pt.h = 0.0;
	
	PROJ_LINE L;
	L.E = &E;
	L.pt1 = &src_pt;
	L.pt2 = &dst_pt;

	src_pt.lam = /* longitude in radians */;
	src_pt.phi = /* latitude in radians */;

	dst_pt.lam = /* longitude in radians */;
	dst_pt.phi = /* latitude in radians */;

	proj_ginverse(&L);

	/* Distance now in L.S, azimuths in L.az12 and L.az21 */

On Tue, Nov 30, 2010 at 2:46 PM, Karney, Charles <ckarney at sarnoff.com> wrote:
>
> > From: Evan Miller [emmiller at gmail.com]
> > Sent: Tuesday, November 30, 2010 10:26
> >
> > I am looking for the functionality provided by "geod" and "invgeod"
> > (great circle calculations) wrapped up in a plain C library. I found
> > Charles Karney's Geographic Library, but that's C++.
>
> I'm not sure whether this will help you...  However a C wrapper to
> GeographicLib is a possibility.  For example:
>
> interface.cpp:
> ================================================================
> #include "GeographicLib/Geodesic.hpp"
>
> extern "C"
> void GeodInverse(double lat1, double lon1, double lat2, double lon2,
>                 double *s12, double *azi1, double *azi2) {
>    GeographicLib::Geodesic::WGS84.Inverse(lat1, lon1, lat2, lon2,
>                                           *s12, *azi1, *azi2);
>    return;
> }
> ================================================================
>
> main.c
> ================================================================
> #include <stdio.h>
>
> void GeodInverse(double lat1, double lon1, double lat2, double lon2,
>                 double *s12, double *azi1, double *azi2);
>
> int main() {
>  double lat1, lon1, lat2, lon2;
>  double s12, azi1, azi2;
>  scanf("%lf %lf %lf %lf\n", &lat1, &lon1, &lat2, &lon2);
>  GeodInverse(lat1, lon1, lat2, lon2, &s12, &azi1, &azi2);
>  printf("%.8f %.8f %.3f\n", azi1, azi2, s12);
> }
> ================================================================
>
> Makefile
> ================================================================
> test: main.o interface.o
>        g++ -o $@ $^ -lGeographic -Wl,--rpath -Wl,/usr/local/lib
> main.o: main.c
>        gcc -c $^
> interface.o: interface.cpp
>        g++ -c $^
> ================================================================
>
> make test
> echo 1 2 3 4 | ./test
> 45.14416881 45.21398561 313705.445
>
> --
> Charles Karney <ckarney at sarnoff.com>
> Sarnoff Corporation, Princeton, NJ 08543-5300
>
> Tel: +1 609 734 2312
> Fax: +1 609 734 2662
>
>
>
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--
Evan Miller
http://www.evanmiller.org/