From 3e8ce840c70ee00925210b96738696d1dc445f8f Mon Sep 17 00:00:00 2001
From: Rutger Broekhoff
Date: Tue, 8 Sep 2026 01:36:38 +0200
Subject: UTM projection

---
 server/src/geo/wgs84.cppm | 115 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 115 insertions(+)
 create mode 100644 server/src/geo/wgs84.cppm

(limited to 'server/src/geo/wgs84.cppm')

diff --git a/server/src/geo/wgs84.cppm b/server/src/geo/wgs84.cppm
new file mode 100644
index 0000000..d574d39
--- /dev/null
+++ b/server/src/geo/wgs84.cppm
@@ -0,0 +1,115 @@
+module;
+
+#include <boost/geometry.hpp>
+
+export module routemon:geo.wgs84;
+
+import :geo;
+
+namespace routemon::geo::wgs84 {
+
+using cs = bgeo::cs::geographic<bgeo::degree>;
+using point = bgeo::model::point<double, 2, cs>;
+// TODO: guarantee that linestring provides non-static member
+//   auto reserve(std::size_t) -> void
+// Perhaps better yet: guarantee that the backing container is a std::vector.
+using linestring = bgeo::model::linestring<point, std::vector /* the default */>;
+using box = bgeo::model::box<point>;
+using stype = bgeo::srs::spheroid<double>;
+using vincenty_strategy = bgeo::strategy::distance::vincenty<stype>;
+
+auto from_lat_lon(double lat, double lon) -> point
+{
+  return point{lon, lat};
+}
+
+auto lat(point p) -> double
+{
+  return bgeo::get<1>(p);
+}
+
+auto lon(point p) -> double
+{
+  return bgeo::get<0>(p);
+}
+
+// Point p with latitude in [-90, 90] and longitude in [-180, 180)
+auto normalize(point p) -> point
+{
+  // Equivalent degrees in the range [0, 360)
+  auto nonneg_mod360 = [](double t) -> double
+  { return std::remainder(std::remainder(t, 360.0) + 360.0, 360.0); };
+
+  auto p_lon = lon(p);
+  auto p_lat = nonneg_mod360(lat(p)) - 90.0;
+  if (90.0 < p_lat)
+  {
+    assert(p_lat < 270.0);  // by nonneg_mod360
+    p_lon += 180.0;
+    p_lat -= 180.0;
+  }
+  p_lon = nonneg_mod360(p_lon + 180.0) - 180.0;
+
+  return from_lat_lon(p_lat, p_lon);
+}
+
+auto is_normalized(point p) -> bool
+{
+  return -90 <= lat(p) && lat(p) <= 90 && -180 <= lon(p) && lon(p) < 180;
+}
+
+class normalized_point
+{
+  point p_;
+
+public:
+  normalized_point(point p)
+    : p_{is_normalized(p) ? p : normalize(p)}
+  {}
+
+  normalized_point()
+    : p_{}
+  {}
+
+  auto lat() const -> double
+  {
+    return bgeo::get<1>(p_);
+  }
+
+  auto lon() const -> double
+  {
+    return bgeo::get<0>(p_);
+  }
+
+  auto lat(double lat) -> void
+  {
+    if (lat < -90 || lat > 90)
+      throw std::range_error{"latitude out of range"};
+    bgeo::set<1>(p_, lat);
+  }
+
+  auto lon(double lon) -> void
+  {
+    if (lon < -180 || lon > 180)
+      throw std::range_error{"longitude out of range"};
+    bgeo::set<0>(p_, lon);
+  }
+};
+
+class normalized_linestring
+{
+  std::vector<normalized_point> ls_;
+
+public:
+  auto empty() const -> bool
+  {
+    return ls_.empty();
+  }
+
+  auto push_back(normalized_point p) -> void
+  {
+    ls_.push_back(p);
+  }
+};
+
+} // namespace routemon::geo::wgs84
-- 
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