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include/boost/geometry/extensions/gis/io/geojson/geojson_writer.hpp
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| // Boost.Geometry | ||
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| // Copyright (c) 2024 Barend Gehrels, Amsterdam, the Netherlands. | ||
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| // Use, modification and distribution is subject to the Boost Software License, | ||
| // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at | ||
| // http://www.boost.org/LICENSE_1_0.txt) | ||
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| #ifndef BOOST_GEOMETRY_EXTENSIONS_GIS_IO_GEOJSON_WRITER_HPP | ||
| #define BOOST_GEOMETRY_EXTENSIONS_GIS_IO_GEOJSON_WRITER_HPP | ||
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| #include <boost/geometry/core/access.hpp> | ||
| #include <boost/geometry/io/dsv/write.hpp> | ||
| #include <boost/geometry/core/static_assert.hpp> | ||
| #include <boost/geometry/util/constexpr.hpp> | ||
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| #include <iomanip> | ||
| #include <ostream> | ||
| #include <string> | ||
| #include <type_traits> | ||
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| namespace boost { namespace geometry | ||
| { | ||
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| #ifndef DOXYGEN_NO_DISPATCH | ||
| namespace dispatch | ||
| { | ||
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| template <typename GeometryTag> | ||
| struct geojson_feature_type | ||
| { | ||
| BOOST_GEOMETRY_STATIC_ASSERT_FALSE("Not or not yet implemented for this Geometry type.", | ||
| GeometryTag); | ||
| }; | ||
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| template <> | ||
| struct geojson_feature_type<point_tag> { static inline const char* apply() { return "Point"; } }; | ||
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| template <> | ||
| struct geojson_feature_type<segment_tag> { static inline const char* apply() { return "LineString"; } }; | ||
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| template <> | ||
| struct geojson_feature_type<ring_tag> { static inline const char* apply() { return "Polygon"; } }; | ||
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| template <> | ||
| struct geojson_feature_type<linestring_tag> { static inline const char* apply() { return "LineString"; } }; | ||
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| template <> | ||
| struct geojson_feature_type<polygon_tag> { static inline const char* apply() { return "Polygon"; } }; | ||
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| template <> | ||
| struct geojson_feature_type<multi_polygon_tag> { static inline const char* apply() { return "MultiPolygon"; } }; | ||
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| } // namespace dispatch | ||
| #endif | ||
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| /*! | ||
| \brief Helper class to create geojson output | ||
| */ | ||
| struct geojson_writer | ||
| { | ||
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| private: | ||
| std::ostream& m_out; | ||
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| std::size_t feature_count = 0; | ||
| std::size_t property_count = 0; | ||
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| template <typename T> | ||
| void stream_quoted(T const& entry) | ||
| { | ||
| m_out << '"' << entry << '"'; | ||
| } | ||
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| void start_feature() | ||
| { | ||
| end_properties(); | ||
| end_feature(); | ||
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| m_out << (feature_count > 0 ? ",\n" : "") << R"({"type": "Feature")"; | ||
| feature_count++; | ||
| } | ||
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| void start_property() | ||
| { | ||
| // Write a comma, either after the "geometry" tag, or after the previous property | ||
| // If there are no properties yet, start the list of properties | ||
| m_out << "," << (property_count == 0 ? R"("properties": {)" : "") << '\n'; | ||
| property_count++; | ||
| } | ||
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| void end_properties() | ||
| { | ||
| if (property_count > 0) | ||
| { | ||
| m_out << "}\n"; | ||
| property_count = 0; | ||
| } | ||
| } | ||
| void end_feature() | ||
| { | ||
| if (feature_count > 0) | ||
| { | ||
| m_out << "}\n"; | ||
| } | ||
| } | ||
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| public: | ||
| explicit geojson_writer(std::ostream& out) : m_out(out) | ||
| { | ||
| m_out << R"({"type": "FeatureCollection", "features": [)" << '\n'; | ||
| } | ||
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| ~geojson_writer() | ||
| { | ||
| end_properties(); | ||
| end_feature(); | ||
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| m_out << "]}"; | ||
| } | ||
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| // Set a property. It is expected that a feature is already started. | ||
| template <typename T> | ||
| void add_property(std::string const& name, T const& value) | ||
| { | ||
| constexpr bool needs_quotes | ||
| = std::is_same<T, std::string>::value | ||
| || std::is_same<typename std::remove_extent<T>::type, char>::value; | ||
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| start_property(); | ||
| stream_quoted(name); | ||
| m_out << ": "; | ||
| if BOOST_GEOMETRY_CONSTEXPR(needs_quotes) | ||
| { | ||
| stream_quoted(value); | ||
| } | ||
| else | ||
| { | ||
| m_out << std::boolalpha << value; | ||
| } | ||
| } | ||
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| // The method "feature" should be called to start a feature. | ||
| // After that, properties can be added, until a new "feature" is called, | ||
| // or the instance is destructed | ||
| template <typename Geometry> | ||
| void feature(Geometry const& geometry) | ||
| { | ||
| using tag_t = typename tag<Geometry>::type; | ||
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| start_feature(); | ||
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| // Write the comma after either the "Feature" tag | ||
| m_out << ",\n"; | ||
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| // Write the geometry | ||
| m_out << R"("geometry": {"type":)"; | ||
| stream_quoted(dispatch::geojson_feature_type<tag_t>::apply()); | ||
| m_out << R"(, "coordinates": )"; | ||
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| // A ring is modelled as a geojson polygon, and therefore the opening and closing | ||
| // list marks should be duplicated to indicate empty interior rings. | ||
| constexpr bool dup = std::is_same<tag_t, ring_tag>::value; | ||
| const char* list_open = dup ? "[[" : "["; | ||
| const char* list_close = dup ? "]]" : "]"; | ||
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| // Indicate that dsv should close any ring automatically if its model is open | ||
| constexpr bool close = geometry::closure<Geometry>::value == geometry::open; | ||
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| m_out << geometry::dsv(geometry, ", ", "[", "]", ", ", list_open, | ||
| list_close, ",", close) << "}\n"; | ||
| } | ||
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| }; | ||
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| }} // namespace boost::geometry | ||
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| #endif |
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