tippecanoe/projection.c

67 lines
1.4 KiB
C

#include <math.h>
#include "projection.h"
// http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames
void latlon2tile(double lat, double lon, int zoom, unsigned int *x, unsigned int *y) {
double lat_rad = lat * M_PI / 180;
unsigned long long n = 1LL << zoom;
long long llx = n * ((lon + 180) / 360);
long long lly = n * (1 - (log(tan(lat_rad) + 1 / cos(lat_rad)) / M_PI)) / 2;
if (lat >= 85.0511) {
lly = 0;
}
if (lat <= -85.0511) {
lly = n - 1;
}
if (llx < 0) {
llx = 0;
}
if (lly < 0) {
lly = 0;
}
if (llx >= n) {
llx = n - 1;
}
if (lly >= n) {
lly = n - 1;
}
*x = llx;
*y = lly;
}
// http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames
void tile2latlon(unsigned int x, unsigned int y, int zoom, double *lat, double *lon) {
unsigned long long n = 1LL << zoom;
*lon = 360.0 * x / n - 180.0;
*lat = atan(sinh(M_PI * (1 - 2.0 * y / n))) * 180.0 / M_PI;
}
unsigned long long encode(unsigned int wx, unsigned int wy) {
long long out = 0;
int i;
for (i = 0; i < 32; i++) {
long long v = ((wx >> (32 - (i + 1))) & 1) << 1;
v |= (wy >> (32 - (i + 1))) & 1;
v = v << (64 - 2 * (i + 1));
out |= v;
}
return out;
}
void decode(unsigned long long index, unsigned *wx, unsigned *wy) {
*wx = *wy = 0;
int i;
for (i = 0; i < 32; i++) {
*wx |= ((index >> (64 - 2 * (i + 1) + 1)) & 1) << (32 - (i + 1));
*wy |= ((index >> (64 - 2 * (i + 1) + 0)) & 1) << (32 - (i + 1));
}
}