WKT2:2019 import/export: handle DATUM (at top level object) with PRIMEM

This is a peculiarity of the WKT grammar. Despite ISO 19111 saying that the
prime meridian is a component of the datum, in WKT, they are placed at the
same level, for backward compatibility with earlier WKT versions. So handle
exporting and importing that. The fix is only for situation where DATUM is
the top level object (was working fine otherwise), which is a uncommon use
case. And to limit the amount of issue, on export emit the prime meridian only
if it is not Greenwich.

1 files changed, 22 insertions, 0 deletions

diff --git a/test/unit/test_io.cpp b/test/unit/test_io.cpp
index 34396fcf..47e574c5 100644
--- a/test/unit/test_io.cpp
+++ b/test/unit/test_io.cpp
@@ -190,6 +190,28 @@ TEST(wkt_parse, datum_with_ANCHOR) {
 
 // ---------------------------------------------------------------------------
 
+TEST(wkt_parse, datum_with_pm) {
+    const char *wkt =
+        "DATUM[\"Nouvelle Triangulation Francaise (Paris)\",\n"
+        "    ELLIPSOID[\"Clarke 1880 (IGN)\",6378249.2,293.466021293627,\n"
+        "        LENGTHUNIT[\"metre\",1]],\n"
+        "    ID[\"EPSG\",6807]],\n"
+        "PRIMEM[\"Paris\",2.5969213,\n"
+        "    ANGLEUNIT[\"grad\",0.0157079632679489],\n"
+        "    ID[\"EPSG\",8903]]";
+
+    auto obj = WKTParser().createFromWKT(wkt);
+    auto datum = nn_dynamic_pointer_cast<GeodeticReferenceFrame>(obj);
+    ASSERT_TRUE(datum != nullptr);
+    EXPECT_EQ(datum->primeMeridian()->nameStr(), "Paris");
+    EXPECT_EQ(
+        datum->exportToWKT(
+            WKTFormatter::create(WKTFormatter::Convention::WKT2_2019).get()),
+        wkt);
+}
+
+// ---------------------------------------------------------------------------
+
 TEST(wkt_parse, datum_no_pm_not_earth) {
     auto obj = WKTParser().createFromWKT("DATUM[\"unnamed\",\n"
                                          "    ELLIPSOID[\"unnamed\",1,0,\n"