forked from mpusz/mp-units
63 lines
2.4 KiB
C++
63 lines
2.4 KiB
C++
// The MIT License (MIT)
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//
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// Copyright (c) 2018 Mateusz Pusz
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in all
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// copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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// SOFTWARE.
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#include "geographic.h"
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#include <cmath>
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#include <numbers>
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namespace {
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using namespace units::isq::si::references;
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inline constexpr auto earth_radius = 6371 * km;
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} // namespace
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namespace geographic {
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distance spherical_distance(position from, position to)
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{
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using rep = std::common_type_t<latitude::value_type, longitude::value_type>;
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constexpr auto p = std::numbers::pi_v<rep> / 180;
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const auto lat1 = from.lat.value() * p;
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const auto lon1 = from.lon.value() * p;
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const auto lat2 = to.lat.value() * p;
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const auto lon2 = to.lon.value() * p;
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using std::sin, std::cos, std::asin, std::sqrt;
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// https://en.wikipedia.org/wiki/Great-circle_distance#Formulae
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if constexpr (sizeof(rep) >= 8) {
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// spherical law of cosines
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const auto central_angle = acos(sin(lat1) * sin(lat2) + cos(lat1) * cos(lat2) * cos(lon2 - lon1));
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// const auto central_angle = 2 * asin(sqrt(0.5 - cos(lat2 - lat1) / 2 + cos(lat1) * cos(lat2) * (1 - cos(lon2 - lon1)) / 2));
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return distance(earth_radius * central_angle);
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} else {
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// the haversine formula
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const auto sin_lat = sin(lat2 - lat1) / 2;
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const auto sin_lon = sin(lon2 - lon1) / 2;
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const auto central_angle = 2 * asin(sqrt(sin_lat * sin_lat + cos(lat1) * cos(lat2) * sin_lon * sin_lon));
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return distance(earth_radius * central_angle);
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}
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}
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} // namespace geographic
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