Simplify: Preserve dimensions of empty geometries (#1357)

* DouglasPeuckerSimplifier: Preserve dimension of empty geometries

* TopologyPreservingSimplifier: Add test for preservation of empty geometry dims

Author: dbaston

include/geos/simplify/DouglasPeuckerSimplifier.h

@@ -68,7 +68,7 @@ class GEOS_DLL DouglasPeuckerSimplifier {
      */
     void setDistanceTolerance(double tolerance);
 
-    std::unique_ptr<geom::Geometry> getResultGeometry();
+    std::unique_ptr<geom::Geometry> getResultGeometry() const;
 
 
 private:

src/simplify/DouglasPeuckerSimplifier.cpp

@@ -201,8 +201,12 @@ DouglasPeuckerSimplifier::setDistanceTolerance(double tol)
 }
 
 Geometry::Ptr
-DouglasPeuckerSimplifier::getResultGeometry()
+DouglasPeuckerSimplifier::getResultGeometry() const
 {
+    if (inputGeom->isEmpty()) {
+        return inputGeom->clone();
+    }
+
     DPTransformer t(distanceTolerance);
     return t.transform(inputGeom);
 

tests/unit/simplify/DouglasPeuckerSimplifierTest.cpp

@@ -37,7 +37,7 @@ struct test_dpsimp_data {
     {}
 
     void
-    checkDP(const std::string& wkt, double tolerance, const std::string& wkt_expected)
+    checkDP(const std::string& wkt, double tolerance, const std::string& wkt_expected) const
     {
         GeomPtr g(wktreader.read(wkt));
         GeomPtr simplified = DouglasPeuckerSimplifier::simplify(g.get(), tolerance);
@@ -49,7 +49,7 @@ struct test_dpsimp_data {
     }
 
     void
-    checkDPNoChange(const std::string& wkt, double tolerance)
+    checkDPNoChange(const std::string& wkt, double tolerance) const
     {
         checkDP(wkt, tolerance, wkt);
     }
@@ -382,4 +382,24 @@ void object::test<23>()
         "POLYGON ZM ((2 0 10 9, 2 2 15 11, 0 2 20 13, 0 0 25 15, 2 0 10 9))");
 }
 
+template<>
+template<>
+void object::test<24>()
+{
+    set_test_name("simplification preserves dimensions of empty geometries");
+
+    const std::vector<std::string> geomTypes{"POINT", "LINESTRING", "POLYGON"};
+    const std::vector<std::string> dimensions{"", "Z", "M", "ZM"};
+    const std::vector<std::string> mods{"", "MULTI"};
+
+    for (const auto& geomType : geomTypes) {
+        for (const auto& dimension: dimensions) {
+            for (const auto& mod: mods) {
+                std::string wkt = mod + geomType + " " + dimension + " EMPTY";
+                checkDP(wkt, 0, wkt);
+            }
+        }
+    }
+}
+
 } // namespace tut

tests/unit/simplify/TopologyPreservingSimplifierTest.cpp

@@ -34,17 +34,17 @@ struct test_tpsimp_data {
     }
 
     void
-    checkTPS(const std::string& wkt, double tolerance, const std::string& wkt_expected)
+    checkTPS(const std::string& wkt, double tolerance, const std::string& wkt_expected) const
     {
         GeomPtr g(wktreader.read(wkt));
         GeomPtr simplified = TopologyPreservingSimplifier::simplify(g.get(), tolerance);
         GeomPtr exp(wktreader.read(wkt_expected));
-        ensure_equals_geometry(exp.get(), simplified.get(),0.00001);
+        ensure_equals_geometry_xyzm(exp.get(), simplified.get(),0.00001);
         ensure("Simplified geometry is invalid!", simplified->isValid());
     }
 
     void
-    checkTPSNoChange(const std::string& wkt, double tolerance)
+    checkTPSNoChange(const std::string& wkt, double tolerance) const
     {
         checkTPS(wkt, tolerance, wkt);
     }
@@ -453,4 +453,24 @@ void object::test<35>()
         "MULTIPOLYGON (((689.300102 5733.615673, 689.46186 5733.617409, 689.458981 5733.646089, 689.300102 5733.615673)), ((689.488158 5733.746304, 689.23796 5733.680098, 689.253227 5733.613915, 689.467162 5733.67151, 689.679568 5733.588383, 689.488158 5733.746304)))");
 }
 
+template<>
+template<>
+void object::test<36>()
+{
+    set_test_name("simplification preserves dimensions of empty geometries");
+
+    const std::vector<std::string> geomTypes{"POINT", "LINESTRING", "POLYGON"};
+    const std::vector<std::string> dimensions{"", "Z", "M", "ZM"};
+    const std::vector<std::string> mods{"", "MULTI"};
+
+    for (const auto& geomType : geomTypes) {
+        for (const auto& dimension: dimensions) {
+            for (const auto& mod: mods) {
+                std::string wkt = mod + geomType + " " + dimension + " EMPTY";
+                checkTPSNoChange(wkt, 0);
+            }
+        }
+    }
+}
+
 } // namespace tut