Fix TopologyPreservingSimplifier endpoint handling to avoid self-inte…

…rsections (#986)
libgeos · Nov 7, 2023 · 1fc2612 · 1fc2612
1 parent bb2db23
commit 1fc2612
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Showing 3 changed files with 53 additions and 18 deletions.
diff --git a/include/geos/simplify/TaggedLineStringSimplifier.h b/include/geos/simplify/TaggedLineStringSimplifier.h
@@ -113,12 +113,12 @@ class GEOS_DLL TaggedLineStringSimplifier {
         double& maxDistance);
 
     bool hasBadIntersection(const TaggedLineString* parentLine,
-                            const std::pair<std::size_t, std::size_t>& sectionIndex,
+                            const size_t excludeStart, const size_t excludeEnd,
                             const geom::LineSegment& candidateSeg);
 
     bool hasBadInputIntersection(const TaggedLineString* parentLine,
-                                 const std::pair<std::size_t, std::size_t>& sectionIndex,
-                                 const geom::LineSegment& candidateSeg);
+                                const size_t excludeStart, const size_t excludeEnd,
+                                const geom::LineSegment& candidateSeg);
 
     bool hasBadOutputIntersection(const geom::LineSegment& candidateSeg);
 
@@ -129,16 +129,20 @@ class GEOS_DLL TaggedLineStringSimplifier {
         std::size_t start, std::size_t end);
 
     /** \brief
-     * Tests whether a segment is in a section of a TaggedLineString
+     * Tests whether a segment is in a section of a TaggedLineString.
+     * Sections may wrap around the endpoint of the line, 
+     * to support ring endpoint simplification.
+     * This is indicated by excludedStart > excludedEnd
      *
      * @param line line to be checked for the presence of `seg`
-     * @param sectionIndex start and end indices of the section to check
+     * @param excludeStart  the index of the first segment in the excluded section  
+     * @param excludeEnd the index of the last segment in the excluded section
      * @param seg segment to look for in `line`
-     * @return
+     * @return true if the test segment intersects some segment in the line not in the excluded section
      */
     static bool isInLineSection(
         const TaggedLineString* line,
-        const std::pair<std::size_t, std::size_t>& sectionIndex,
+        const size_t excludeStart, const size_t excludeEnd,
         const TaggedLineSegment* seg);
 
     /** \brief

diff --git a/src/simplify/TaggedLineStringSimplifier.cpp b/src/simplify/TaggedLineStringSimplifier.cpp
@@ -38,7 +38,6 @@
 #endif
 
 using namespace geos::geom;
-using std::pair;
 using std::unique_ptr;
 using std::vector;
 
@@ -149,7 +148,7 @@ TaggedLineStringSimplifier::simplifySection(std::size_t i,
     // test if flattened section would cause intersection
     LineSegment candidateSeg(linePts->getAt(i), linePts->getAt(j));
 
-    if(hasBadIntersection(line, std::make_pair(i, j), candidateSeg)) {
+    if(hasBadIntersection(line, i, j, candidateSeg)) {
         isValidToSimplify = false;
     }
 
@@ -182,8 +181,8 @@ TaggedLineStringSimplifier::simplifyRingEndpoint()
 
         LineSegment candidateSeg(lastSeg->p0, firstSeg->p1);
         if (candidateSeg.distance(firstSeg->p0) <= distanceTolerance &&
-                !hasBadIntersection(line, std::make_pair(0, line->getSegments().size()), candidateSeg)) {
-            auto newSeg = detail::make_unique<TaggedLineSegment>(candidateSeg.p0, candidateSeg.p1);
+                ! hasBadIntersection(line, line->getSegments().size() - 2, 0, candidateSeg)) {
+            //auto newSeg = detail::make_unique<TaggedLineSegment>(candidateSeg.p0, candidateSeg.p1);
             line->removeRingEndpoint();
         }
     }
@@ -207,14 +206,14 @@ TaggedLineStringSimplifier::flatten(std::size_t start, std::size_t end)
 bool
 TaggedLineStringSimplifier::hasBadIntersection(
     const TaggedLineString* parentLine,
-    const pair<size_t, size_t>& sectionIndex,
+    const size_t excludeStart, const size_t excludeEnd,
     const LineSegment& candidateSeg)
 {
     if(hasBadOutputIntersection(candidateSeg)) {
         return true;
     }
 
-    if(hasBadInputIntersection(parentLine, sectionIndex, candidateSeg)) {
+    if(hasBadInputIntersection(parentLine, excludeStart, excludeEnd, candidateSeg)) {
         return true;
     }
 
@@ -252,15 +251,15 @@ TaggedLineStringSimplifier::hasInteriorIntersection(
 bool
 TaggedLineStringSimplifier::hasBadInputIntersection(
     const TaggedLineString* parentLine,
-    const pair<std::size_t, std::size_t>& sectionIndex,
+    const size_t excludeStart, const size_t excludeEnd,
     const LineSegment& candidateSeg)
 {
     const auto& foundSegs = inputIndex->query(&candidateSeg);
 
     for(const LineSegment* ls : *foundSegs) {
         const TaggedLineSegment* foundSeg = static_cast<const TaggedLineSegment*>(ls);
 
-        if(!isInLineSection(parentLine, sectionIndex, foundSeg) && hasInteriorIntersection(*foundSeg, candidateSeg)) {
+        if(!isInLineSection(parentLine, excludeStart, excludeEnd, foundSeg) && hasInteriorIntersection(*foundSeg, candidateSeg)) {
             return true;
         }
     }
@@ -272,7 +271,7 @@ TaggedLineStringSimplifier::hasBadInputIntersection(
 bool
 TaggedLineStringSimplifier::isInLineSection(
     const TaggedLineString* line,
-    const pair<size_t, size_t>& sectionIndex,
+    const size_t excludeStart, const size_t excludeEnd,
     const TaggedLineSegment* seg)
 {
     // not in this line
@@ -281,10 +280,16 @@ TaggedLineStringSimplifier::isInLineSection(
     }
 
     std::size_t segIndex = seg->getIndex();
-    if(segIndex >= sectionIndex.first && segIndex < sectionIndex.second) {
+    if (excludeStart <= excludeEnd) {
+      //-- section is contiguous
+      if (segIndex >= excludeStart && segIndex < excludeEnd)
         return true;
     }
-
+    else {
+      //-- section wraps around the end of a ring
+      if (segIndex >= excludeStart || segIndex <= excludeEnd)
+      return true;
+    }
     return false;
 }
 

diff --git a/tests/unit/simplify/TopologyPreservingSimplifierTest.cpp b/tests/unit/simplify/TopologyPreservingSimplifierTest.cpp
@@ -34,6 +34,18 @@ struct test_tpsimp_data {
         , wktwriter()
     {
     }
+
+    void
+    checkTPS(const std::string& wkt, double tolerance, const std::string& wkt_expected)
+    {
+        GeomPtr g(wktreader.read(wkt));
+        GeomPtr simplified = TopologyPreservingSimplifier::simplify(g.get(), tolerance);
+
+        ensure("Simplified geometry is invalid!", simplified->isValid());
+
+        GeomPtr exp(wktreader.read(wkt_expected));
+        ensure_equals_geometry(exp.get(), simplified.get());
+    }
 };
 
 typedef test_group<test_tpsimp_data> group;
@@ -379,4 +391,18 @@ void object::test<18>
     ensure_equals_geometry(simplified.get(), g.get());
 }
 
+// testPolygonKeepEndpointWithCross
+// Test that endpoint is not simplified if it breaks topology
+template<>
+template<>
+void object::test<19>
+()
+{
+    checkTPS(
+      "POLYGON ((50 52, 60 50, 90 60, 90 10, 10 10, 10 90, 60 90, 50 55, 40 80, 20 60, 40 50, 50 52))",
+        10,
+        "POLYGON ((50 52, 90 60, 90 10, 10 10, 10 90, 60 90, 50 55, 40 80, 20 60, 50 52))"
+        );
+}
+
 } // namespace tut