refactor: common part of glide_computer moved to a directory

example/glide_computer/geographic.cpp

@@ -0,0 +1,63 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Mateusz Pusz
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "geographic.h"
+#include <cmath>
+#include <numbers>
+#include <type_traits>
+
+namespace {
+
+using namespace units::isq::si;
+inline constexpr length<kilometre> earth_radius(6371);
+
+}  // namespace
+
+namespace geographic {
+
+distance spherical_distance(position from, position to)
+{
+  using rep = std::common_type_t<latitude::value_type, longitude::value_type>;
+  constexpr auto p = std::numbers::pi_v<rep> / 180;
+  const auto lat1 = from.lat.value() * p;
+  const auto lon1 = from.lon.value() * p;
+  const auto lat2 = to.lat.value() * p;
+  const auto lon2 = to.lon.value() * p;
+
+  using std::sin, std::cos, std::asin, std::sqrt;
+
+  // https://en.wikipedia.org/wiki/Great-circle_distance#Formulae
+  if constexpr (sizeof(rep) >= 8) {
+    // spherical law of cosines
+    const auto central_angle = acos(sin(lat1) * sin(lat2) + cos(lat1) * cos(lat2) * cos(lon2 - lon1));
+    // const auto central_angle = 2 * asin(sqrt(0.5 - cos(lat2 - lat1) / 2 + cos(lat1) * cos(lat2) * (1 - cos(lon2 - lon1)) / 2));
+    return distance(earth_radius * central_angle);
+  } else {
+    // the haversine formula
+    const auto sin_lat = sin(lat2 - lat1) / 2;
+    const auto sin_lon = sin(lon2 - lon1) / 2;
+    const auto central_angle = 2 * asin(sqrt(sin_lat * sin_lat + cos(lat1) * cos(lat2) * sin_lon * sin_lon));
+    return distance(earth_radius * central_angle);
+  }
+}
+
+}  // namespace geographic