From 8f7a7df145b8fe47373c861927bbc6a0ad6be0d4 Mon Sep 17 00:00:00 2001
From: Mike Taves <mwtoews@gmail.com>
Date: Wed, 15 Jan 2025 13:17:31 +1300
Subject: [PATCH] Fix invalid values from CoverageUnionNG (#1226)

---
 src/operation/overlayng/CoverageUnion.cpp     |  6 ++--
 .../overlayng/CoverageUnionNGTest.cpp         | 30 +++++++++++++++++++
 2 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/src/operation/overlayng/CoverageUnion.cpp b/src/operation/overlayng/CoverageUnion.cpp
index c0c8a14581..3d860c92a7 100644
--- a/src/operation/overlayng/CoverageUnion.cpp
+++ b/src/operation/overlayng/CoverageUnion.cpp
@@ -33,7 +33,6 @@ namespace overlayng { // geos.operation.overlayng
 std::unique_ptr<Geometry>
 CoverageUnion::geomunion(const Geometry* coverage)
 {
-    double area_in = coverage->getArea();
     std::unique_ptr<Geometry> result;
 
     // a precision model is not needed since no noding is done
@@ -47,9 +46,10 @@ CoverageUnion::geomunion(const Geometry* coverage)
         result = OverlayNG::geomunion(coverage, nullptr, &bcn);
     }
 
-    double area_out = result->getArea();
+    double area_in = coverage->getArea();
 
-    if (std::abs((area_out - area_in)/area_in) > AREA_PCT_DIFF_TOL) {
+    if ( (area_in != 0.0) &&
+         (std::abs((result->getArea() - area_in)/area_in) > AREA_PCT_DIFF_TOL)) {
         throw geos::util::TopologyException("CoverageUnion cannot process overlapping inputs.");
     }
 
diff --git a/tests/unit/operation/overlayng/CoverageUnionNGTest.cpp b/tests/unit/operation/overlayng/CoverageUnionNGTest.cpp
index aec919b207..86d8ac9486 100644
--- a/tests/unit/operation/overlayng/CoverageUnionNGTest.cpp
+++ b/tests/unit/operation/overlayng/CoverageUnionNGTest.cpp
@@ -8,6 +8,7 @@
 #include <geos/operation/overlayng/CoverageUnion.h>
 
 // std
+#include <cfenv>
 #include <memory>
 
 using namespace geos::geom;
@@ -31,7 +32,9 @@ struct test_coverageunionng_data {
     {
         std::unique_ptr<Geometry> geom = r.read(wkt);
         std::unique_ptr<Geometry> expected = r.read(wktExpected);
+        std::feclearexcept(FE_ALL_EXCEPT);
         std::unique_ptr<Geometry> result = CoverageUnion::geomunion(geom.get());
+        ensure("FE_INVALID raised", !std::fetestexcept(FE_INVALID));
 
         try {
             ensure_equals_geometry_xyzm(result.get(), expected.get());
@@ -220,4 +223,31 @@ void object::test<17>()
                "POLYGON M ((0 0 0, 1 0 1, 1 1 2, 0 1 3, 0 0 0))");
 }
 
+// Check empty polygon
+template<>
+template<>
+void object::test<18>()
+{
+    checkUnion("POLYGON EMPTY",
+               "POLYGON EMPTY");
+}
+
+// Check empty GeometryCollection, with M dimension
+template<>
+template<>
+void object::test<19>()
+{
+    checkUnion("GEOMETRYCOLLECTION M EMPTY",
+               "GEOMETRYCOLLECTION M EMPTY");
+}
+
+// Check GeometryCollection of empty polygon
+template<>
+template<>
+void object::test<20>()
+{
+    checkUnion("GEOMETRYCOLLECTION( POLYGON EMPTY )",
+               "POLYGON EMPTY");
+}
+
 } // namespace tut