distance calculations
Darrell McCauley
mccauley at ecn.purdue.edu
Sat Jul 31 23:29:49 EDT 1993
I'm trying to do distance calculations. Here's a full sample
program:
#include <math.h>
#include "gis.h"
int main (argc, argv)
char **argv;
int argc;
{
double x1=8.0,y1=7.0,x2=6.0,y2=5.0;
G_gisinit (argv[0]);
printf ("projection: %d\n", G_begin_distance_calculations());
printf ("G_distance: %g\n", G_distance (x1,y1,x2,y2));
printf (" hypot: %g\n", hypot (x1-x2,y1-y2));
}
Is there any thing wrong with this? I run this simple
program under (x,y), LL, and utm, I get the same answers:
GRASS 4.1 > simple
projection: 0
G_distance: 8
hypot: 2.82843
(that is, except for the projection). A distance of 8 is clearly
wrong.
I am linking the math library and $(GISLIB) when compiling.
G_distance should just return factor*hypot (x1-x2,y1-y2), where
G_begin_distance_calculations() initializes factor to be 1.0
(for utm and x-y).
What's going on here? %-|
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