1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
|
* Takes degrees lat/long pairs,
* Returns miles + compass degrees
* Bart Massey 2000
* From Javascript by Jeff Waldock 1997
* http://jeff.sci.shu.ac.uk/jw/javascript/js2.html
*
* XXX Appears to need some angle reductions: the bearing
* may be off by a multiple of 90 degrees.
*/
typedef struct {
real lat, lon;
} loc;
typedef struct {
real dist, bearing;
} course;
course great_circle (loc start, loc end) {
real rad = pi / 180;
/* real earth_radius = 6371.2 km ; */
real earth_radius = 3958.9; /* miles */
real a = (90 - start.lat) * rad;
real b = (90 - end.lat) * rad;
real phi = (end.lon - start.lon) * rad;
real cosr = cos(a) * cos(b) + sin(a) * sin(b) * cos(phi);
real r = acos(cosr);
real rdist = earth_radius * r;
real sinth = sin(phi) * sin(b) / sin(r);
real th = asin(sinth) / rad;
return (course){ .dist = rdist, .bearing = th };
}
|
