From 7358a66c2ffc288823bde5a5dc46395e245369fa Mon Sep 17 00:00:00 2001
From: Artem Pavlenko <artem@mapnik.org>
Date: Mon, 29 Jul 2024 11:21:54 +0100
Subject: [PATCH] mapnik::projection - add `area_of_use` method returning
 `std::optional<mapnik::box2d<double>>` (WGS84) [WIP] [skip ci]

---
 include/mapnik/projection.hpp |  9 +++++----
 src/projection.cpp            | 12 +++++++++++-
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/include/mapnik/projection.hpp b/include/mapnik/projection.hpp
index dd3183889..032b1370b 100644
--- a/include/mapnik/projection.hpp
+++ b/include/mapnik/projection.hpp
@@ -26,7 +26,7 @@
 // mapnik
 #include <mapnik/config.hpp>
 #include <mapnik/well_known_srs.hpp>
-
+#include <mapnik/geometry/box2d.hpp>
 #include <mapnik/warning.hpp>
 MAPNIK_DISABLE_WARNING_PUSH
 #include <mapnik/warning_ignore.hpp>
@@ -79,15 +79,16 @@ class MAPNIK_DECL projection
     void inverse(double& x, double& y) const;
     std::string definition() const;
     std::string description() const;
-    void init_proj() const;
-
+    void init_proj();
+    std::optional<box2d<double>> area_of_use() const;
   private:
     void swap(projection& rhs);
 
   private:
     std::string params_;
     bool defer_proj_init_;
-    mutable bool is_geographic_;
+    bool is_geographic_;
+    std::optional<box2d<double>> area_of_use_;
     mutable PJ* proj_;
     mutable PJ_CONTEXT* proj_ctx_;
 };
diff --git a/src/projection.cpp b/src/projection.cpp
index 29cffb4d8..6b434a175 100644
--- a/src/projection.cpp
+++ b/src/projection.cpp
@@ -94,7 +94,7 @@ bool projection::operator!=(const projection& other) const
     return !(*this == other);
 }
 
-void projection::init_proj() const
+void projection::init_proj()
 {
 #ifdef MAPNIK_USE_PROJ
     if (!proj_)
@@ -117,6 +117,11 @@ void projection::init_proj() const
         }
         PJ_TYPE type = proj_get_type(proj_);
         is_geographic_ = (type == PJ_TYPE_GEOGRAPHIC_2D_CRS || type == PJ_TYPE_GEOGRAPHIC_3D_CRS) ? true : false;
+        double west_lon, south_lat, east_lon, north_lat;
+        if (proj_get_area_of_use(proj_ctx_, proj_, &west_lon, &south_lat, &east_lon, &north_lat, nullptr))
+        {
+            area_of_use_ = box2d<double>{west_lon, south_lat, east_lon, north_lat};
+        }
     }
 #endif
 }
@@ -131,6 +136,11 @@ bool projection::is_geographic() const
     return is_geographic_;
 }
 
+std::optional<box2d<double>> projection::area_of_use() const
+{
+    return area_of_use_;
+}
+
 std::optional<well_known_srs_e> projection::well_known() const
 {
     return is_well_known_srs(params_);