First commit

LICENSE

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+Boost Software License - Version 1.0 - August 17th, 2003
+
+Permission is hereby granted, free of charge, to any person or organization
+obtaining a copy of the software and accompanying documentation covered by
+this license (the "Software") to use, reproduce, display, distribute,
+execute, and transmit the Software, and to prepare derivative works of the
+Software, and to permit third-parties to whom the Software is furnished to
+do so, all subject to the following:
+
+The copyright notices in the Software and this entire statement, including
+the above license grant, this restriction and the following disclaimer,
+must be included in all copies of the Software, in whole or in part, and
+all derivative works of the Software, unless such copies or derivative
+works are solely in the form of machine-executable object code generated by
+a source language processor.
+
+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, TITLE AND NON-INFRINGEMENT. IN NO EVENT
+SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
+FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
+ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.

README.md

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+# Projection class for Libosmium
+
+This repository contains code for projecting OSM locations to arbitrary
+coordinate reference systems. It is based on the PROJ library. Unlike
+the code which is included in libosmium which only supports older
+PROJ versions, this one is for PROJ version 6 and above.
+
+**This is untested code just provided as a starting point, because libosmium
+doesn't support PROJ 6 and above.**
+
+To use this include `projection.hpp` in your program and instantiate the
+`osmium::geom::GeometryFactory` class with the class `PROJ_Projection` as
+template parameter. See the libosmium documentation for details of how to
+use the `GeometryFactory` class.
+
+You need to compile with `libproj`.
+

projection.hpp

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+#once
+
+#include <osmium/geom/coordinates.hpp>
+#include <osmium/geom/mercator_projection.hpp>
+#include <osmium/geom/util.hpp>
+#include <osmium/osm/location.hpp>
+
+#include <proj.h>
+
+#include <cassert>
+#include <memory>
+#include <string>
+
+
+/**
+ * Functor that does projection from WGS84 (EPSG:4326) to the given
+ * CRS.
+ *
+ * If this Projection is initialized with the constructor taking
+ * an integer with the epsg code 4326, no projection is done. If it
+ * is initialized with epsg code 3857 the Osmium-internal
+ * implementation of the Mercator projection is used, otherwise this
+ * falls back to using the PROJ library. Note that this "magic" does
+ * not work if you use any of the constructors taking a string.
+ */
+class PROJ_Projection {
+
+    struct ProjDestroyer {
+        void operator()(PJ* crs) {
+            proj_destroy(crs);
+        }
+    }; // struct ProjDestroyer
+
+    std::string m_proj_string;
+    std::unique_ptr<PJ, ProjDestroyer> m_proj;
+    int m_epsg = -1;
+
+    PJ* make_proj(const char* to_crs) {
+        PJ* p = proj_create_crs_to_crs(PJ_DEFAULT_CTX,
+                                       "EPSG:4326", to_crs,
+                                       nullptr);
+        if (p) {
+            return p;
+        }
+
+        throw osmium::projection_error{std::string{"Creating PROJ projection failed: "} +
+                                       proj_errno_string(proj_errno(p))};
+    }
+
+public:
+
+    explicit Projection(const char* proj_string) :
+        m_proj_string(proj_string),
+        m_proj(make_proj(proj_string)) {
+    }
+
+    explicit Projection(const std::string& proj_string) :
+        Projection(proj_string.c_str()) {
+    }
+
+    explicit Projection(int epsg) :
+        m_proj_string(std::string{"EPSG:"} + std::to_string(epsg)),
+        m_proj((epsg == 4326 || epsg == 3857) ? nullptr
+                                              : make_proj(m_proj_string.c_str())),
+        m_epsg(epsg) {
+    }
+
+    /**
+     * Do coordinate transformation.
+     *
+     * @pre Location must be in valid range (depends on projection used).
+     */
+    Coordinates operator()(osmium::Location location) const {
+        if (m_epsg == 4326) {
+            return Coordinates{location.lon(), location.lat()};
+        }
+
+        if (m_epsg == 3857) {
+            return Coordinates{detail::lon_to_x(location.lon()),
+                               detail::lat_to_y(location.lat())};
+        }
+
+        PJ_COORD from;
+        from.lpzt.z = 0.0;
+        from.lpzt.t = HUGE_VAL;
+        from.lpzt.lam = location.lon();
+        from.lpzt.phi = location.lat();
+
+        assert(m_proj);
+        PJ_COORD to = proj_trans(m_proj.get(), PJ_FWD, from);
+
+        return Coordinates{to.xy.x, to.xy.y};
+    }
+
+    int epsg() const noexcept {
+        return m_epsg;
+    }
+
+}; // class PROJ_Projection
+