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/*
* Copyright 2018, 2020-2021 Uber Technologies, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* Example program that calculates the distance in hexagons and in kilometers
* between two hexagon indices.
*/
// mean Earth radius
#define R 6371.0088
#include <assert.h>
#include <h3/h3api.h>
#include <inttypes.h>
#include <math.h>
#include <stdio.h>
/**
* @brief haversineDistance finds the
* [great-circle distance](https://en.wikipedia.org/wiki/Great-circle_distance)
* between two points on a sphere.
* @see https://en.wikipedia.org/wiki/Haversine_formula.
*
* Parameters are the latitude and longitude of the first and second point in
* radians, respectively.
*
* @return the great-circle distance in kilometers.
*/
double haversineDistance(double th1, double ph1, double th2, double ph2) {
double dx, dy, dz;
ph1 -= ph2;
dz = sin(th1) - sin(th2);
dx = cos(ph1) * cos(th1) - cos(th2);
dy = sin(ph1) * cos(th1);
return asin(sqrt(dx * dx + dy * dy + dz * dz) / 2) * 2 * R;
}
int main(int argc, char *argv[]) {
// 1455 Market St @ resolution 15
H3Index h3HQ1 = 0;
stringToH3("8f2830828052d25", &h3HQ1);
// 555 Market St @ resolution 15
H3Index h3HQ2 = 0;
stringToH3("8f283082a30e623", &h3HQ2);
LatLng geoHQ1 = {0};
LatLng geoHQ2 = {0};
cellToLatLng(h3HQ1, &geoHQ1);
cellToLatLng(h3HQ2, &geoHQ2);
int64_t distance = 0;
assert(gridDistance(h3HQ1, h3HQ2, &distance) == E_SUCCESS);
printf(
"origin: (%lf, %lf)\n"
"destination: (%lf, %lf)\n"
"grid distance: %" PRId64
"\n"
"distance in km: %lfkm\n",
radsToDegs(geoHQ1.lat), radsToDegs(geoHQ1.lng), radsToDegs(geoHQ2.lat),
radsToDegs(geoHQ2.lng), distance,
haversineDistance(geoHQ1.lat, geoHQ1.lng, geoHQ2.lat, geoHQ2.lng));
// Output:
// origin: (37.775236, -122.419755)
// destination: (37.789991, -122.402121)
// grid distance: 2340
// distance in km: 2.256853km
}
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