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64 lines
1.5 KiB
C
64 lines
1.5 KiB
C
#include <math.h>
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#include "projection.h"
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// http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames
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void latlon2tile(double lat, double lon, int zoom, long long *x, long long *y) {
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// Must limit latitude somewhere to prevent overflow.
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// 89.9 degrees latitude is 0.621 worlds beyond the edge of the flat earth,
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// hopefully far enough out that there are few expectations about the shape.
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if (lat < -89.9) {
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lat = -89.9;
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}
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if (lat > 89.9) {
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lat = 89.9;
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}
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if (lon < -360) {
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lon = -360;
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}
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if (lon > 360) {
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lon = 360;
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}
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double lat_rad = lat * M_PI / 180;
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unsigned long long n = 1LL << zoom;
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long long llx = n * ((lon + 180) / 360);
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long long lly = n * (1 - (log(tan(lat_rad) + 1 / cos(lat_rad)) / M_PI)) / 2;
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*x = llx;
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*y = lly;
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}
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// http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames
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void tile2latlon(long long x, long long y, int zoom, double *lat, double *lon) {
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unsigned long long n = 1LL << zoom;
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*lon = 360.0 * x / n - 180.0;
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*lat = atan(sinh(M_PI * (1 - 2.0 * y / n))) * 180.0 / M_PI;
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}
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unsigned long long encode(unsigned int wx, unsigned int wy) {
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unsigned long long out = 0;
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int i;
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for (i = 0; i < 32; i++) {
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unsigned long long v = ((wx >> (32 - (i + 1))) & 1) << 1;
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v |= (wy >> (32 - (i + 1))) & 1;
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v = v << (64 - 2 * (i + 1));
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out |= v;
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}
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return out;
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}
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void decode(unsigned long long index, unsigned *wx, unsigned *wy) {
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*wx = *wy = 0;
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int i;
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for (i = 0; i < 32; i++) {
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*wx |= ((index >> (64 - 2 * (i + 1) + 1)) & 1) << (32 - (i + 1));
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*wy |= ((index >> (64 - 2 * (i + 1) + 0)) & 1) << (32 - (i + 1));
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}
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}
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