From 1ee3b0be4e860b0b76e857075b4f51de01be581b Mon Sep 17 00:00:00 2001
From: Paul Ramsey <pramsey@cleverelephant.ca>
Date: Fri, 15 Nov 2024 14:35:25 -0800
Subject: [PATCH] Fix line->getPoint(n) error with m coordinates GH-1191

---
 src/geom/SimpleCurve.cpp           | 13 ++++++++-
 tests/unit/geom/LineStringTest.cpp | 46 ++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/src/geom/SimpleCurve.cpp b/src/geom/SimpleCurve.cpp
index be9b50b443..6bb589257b 100644
--- a/src/geom/SimpleCurve.cpp
+++ b/src/geom/SimpleCurve.cpp
@@ -251,7 +251,18 @@ SimpleCurve::getPointN(std::size_t n) const
 {
     assert(getFactory());
     assert(points.get());
-    return std::unique_ptr<Point>(getFactory()->createPoint(points->getAt(n)));
+
+    std::unique_ptr<Point> point;
+    if (hasM() || hasZ()) {
+        CoordinateXYZM c;
+        points->getAt(n, c);
+        return getFactory()->createPoint(c);
+    }
+    else {
+        CoordinateXY c;
+        points->getAt(n, c);
+        return getFactory()->createPoint(c);
+    }
 }
 
 std::unique_ptr<Point>
diff --git a/tests/unit/geom/LineStringTest.cpp b/tests/unit/geom/LineStringTest.cpp
index 26a8756bfb..06e1dfa0cf 100644
--- a/tests/unit/geom/LineStringTest.cpp
+++ b/tests/unit/geom/LineStringTest.cpp
@@ -35,6 +35,7 @@ struct test_linestring_data {
     geos::geom::PrecisionModel pm_;
     geos::geom::GeometryFactory::Ptr factory_;
     geos::io::WKTReader reader_;
+    geos::io::WKTWriter writer_;
 
     std::unique_ptr<geos::geom::LineString> empty_line_;
     std::unique_ptr<geos::geom::LineString> line_;
@@ -588,5 +589,50 @@ void object::test<32>
     ensure(!line_->hasDimension(geos::geom::Dimension::A));
 }
 
+// https://github.com/libgeos/geos/issues/1191
+// line->getPoint(n) loses M dimension
+template<>
+template<>
+void object::test<33>
+()
+{
+    auto geom = reader_.read("LINESTRING M (0 1 2, 10 11 12, 20 21 22)");
+    ensure(geom != nullptr);
+    geos::geom::LineString *line = static_cast<LineString*>(geom.get());
+    ensure_equals(line->getCoordinateDimension(), 3);
+    auto pt = line->getPointN(2);
+    auto out = writer_.write(*pt);
+    ensure_equals(out, "POINT M (20 21 22)");
+}
+
+template<>
+template<>
+void object::test<34>
+()
+{
+    auto geom = reader_.read("LINESTRING Z (0 1 2, 10 11 12, 20 21 22)");
+    ensure(geom != nullptr);
+    geos::geom::LineString *line = static_cast<LineString*>(geom.get());
+    ensure_equals(line->getCoordinateDimension(), 3);
+    auto pt = line->getPointN(2);
+    auto out = writer_.write(*pt);
+    ensure_equals(out, "POINT Z (20 21 22)");
+}
+
+template<>
+template<>
+void object::test<35>
+()
+{
+    auto geom = reader_.read("LINESTRING ZM (0 1 2 3, 10 11 12 13, 20 21 22 23)");
+    ensure(geom != nullptr);
+    geos::geom::LineString *line = static_cast<LineString*>(geom.get());
+    ensure_equals(line->getCoordinateDimension(), 4);
+    auto pt = line->getPointN(2);
+    auto out = writer_.write(*pt);
+    ensure_equals(out, "POINT ZM (20 21 22 23)");
+}
+
+
 } // namespace tut