Fix CCW ring buffer generation

libgeos · Feb 12, 2025 · bcd4c34 · bcd4c34
1 parent a6552f8
commit bcd4c34
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Showing 4 changed files with 111 additions and 38 deletions.
diff --git a/include/geos/operation/buffer/BufferCurveSetBuilder.h b/include/geos/operation/buffer/BufferCurveSetBuilder.h
@@ -120,7 +120,7 @@ class GEOS_DLL BufferCurveSetBuilder {
 
     void addPolygon(const geom::Polygon* p);
 
-    void addRingBothSides(const geom::CoordinateSequence* coord, double p_distance);
+    void addLinearRingSides(const geom::CoordinateSequence* coord, double p_distance);
 
     /**
      * Add an offset curve for a polygon ring.
@@ -140,10 +140,14 @@ class GEOS_DLL BufferCurveSetBuilder {
      * @param cwRightLoc the location on the R side of the ring
      *                   (if it is CW)
      */
-    void addRingSide(const geom::CoordinateSequence* coord,
+    void addPolygonRingSide(const geom::CoordinateSequence* coord,
                      double offsetDistance, int side, geom::Location cwLeftLoc,
                      geom::Location cwRightLoc);
 
+    void addRingSide(const geom::CoordinateSequence* coord,
+                     double offsetDistance, int side, geom::Location leftLoc,
+                     geom::Location rightLoc);
+
     /**
      * Tests whether the offset curve for a ring is fully inverted.
      * An inverted ("inside-out") curve occurs in some specific situations

diff --git a/src/operation/buffer/BufferCurveSetBuilder.cpp b/src/operation/buffer/BufferCurveSetBuilder.cpp
@@ -210,16 +210,44 @@ BufferCurveSetBuilder::addLineString(const LineString* line)
      * Singled-sided buffers currently treat rings as if they are lines.
      */
     if (coord->isRing() && ! curveBuilder.getBufferParameters().isSingleSided()) {
-        addRingBothSides(coord.get(), distance);
+        addLinearRingSides(coord.get(), distance);
     }
     else {
         std::vector<CoordinateSequence*> lineList;
         curveBuilder.getLineCurve(coord.get(), distance, lineList);
         addCurves(lineList, Location::EXTERIOR, Location::INTERIOR);
     }
-
 }
 
+/* private */
+void
+BufferCurveSetBuilder::addLinearRingSides(const CoordinateSequence* coord, double p_distance)
+{
+    /*
+     * (f "hole" side will be eroded completely, avoid generating it.
+     * This prevents hole artifacts (e.g. https://github.com/libgeos/geos/issues/1223)
+     */
+    //-- distance is assumed positive, due to previous checks
+    Envelope env;
+    coord->expandEnvelope(env);
+    bool isHoleComputed = ! isRingFullyEroded(coord, &env, true, distance);
+
+    bool isCCW = isRingCCW(coord);
+
+    bool isShellLeft = ! isCCW;
+    if (isShellLeft || isHoleComputed) {
+        addRingSide(coord, p_distance,
+                    Position::LEFT,
+                    Location::EXTERIOR, Location::INTERIOR);
+    }
+
+    bool isShellRight = isCCW;
+    if (isShellRight || isHoleComputed) {
+        addRingSide(coord, p_distance,
+                    Position::RIGHT,
+                    Location::INTERIOR, Location::EXTERIOR);
+    }
+}
 
 /*private*/
 void
@@ -257,7 +285,7 @@ BufferCurveSetBuilder::addPolygon(const Polygon* p)
         return;
     }
 
-    addRingSide(
+    addPolygonRingSide(
         shellCoord.get(),
         offsetDistance,
         offsetSide,
@@ -279,7 +307,7 @@ BufferCurveSetBuilder::addPolygon(const Polygon* p)
         // Holes are topologically labelled opposite to the shell,
         // since the interior of the polygon lies on their opposite
         // side (on the left, if the hole is oriented CCW)
-        addRingSide(
+        addPolygonRingSide(
             holeCoord.get(),
             offsetDistance,
             Position::opposite(offsetSide),
@@ -290,38 +318,7 @@ BufferCurveSetBuilder::addPolygon(const Polygon* p)
 
 /* private */
 void
-BufferCurveSetBuilder::addRingBothSides(const CoordinateSequence* coord, double p_distance)
-{
-    /*
-     * (f "hole" side will be eroded completely, avoid generating it.
-     * This prevents hole artifacts (e.g. https://github.com/libgeos/geos/issues/1223)
-     */
-    //-- distance is assumed positive, due to previous checks
-    Envelope env;
-    coord->expandEnvelope(env);
-    bool isHoleComputed = ! isRingFullyEroded(coord, &env, true, distance);
-
-    bool isCCW = isRingCCW(coord);
-
-    bool isShellLeft = ! isCCW;
-    if (isShellLeft || isHoleComputed) {
-        addRingSide(coord, p_distance,
-                    Position::LEFT,
-                    Location::EXTERIOR, Location::INTERIOR);
-    }
-
-    bool isShellRight = isCCW;
-    if (isShellRight || isHoleComputed) {
-        addRingSide(coord, p_distance,
-                    Position::RIGHT,
-                    Location::INTERIOR, Location::EXTERIOR);
-    }
-}
-
-
-/* private */
-void
-BufferCurveSetBuilder::addRingSide(const CoordinateSequence* coord,
+BufferCurveSetBuilder::addPolygonRingSide(const CoordinateSequence* coord,
                                       double offsetDistance, int side, geom::Location cwLeftLoc, geom::Location cwRightLoc)
 {
 
@@ -353,6 +350,14 @@ BufferCurveSetBuilder::addRingSide(const CoordinateSequence* coord,
 #endif
         side = Position::opposite(side);
     }
+    addRingSide(coord, offsetDistance, side, leftLoc, rightLoc);
+}
+
+/* private */
+void
+BufferCurveSetBuilder::addRingSide(const CoordinateSequence* coord,
+                                      double offsetDistance, int side, geom::Location leftLoc, geom::Location rightLoc)
+{
     std::vector<CoordinateSequence*> lineList;
     curveBuilder.getRingCurve(coord, side, offsetDistance, lineList);
     // ASSERT: lineList contains exactly 1 curve (this is teh JTS semantics)

diff --git a/tests/unit/operation/buffer/BufferOpTest.cpp b/tests/unit/operation/buffer/BufferOpTest.cpp
@@ -585,4 +585,17 @@ void object::test<25>
     checkArea(*result2, 107);
 }
 
+// testRingCCW
+// See https://github.com/libgeos/geos/issues/1236
+template<>
+template<>
+void object::test<26>
+()
+{
+    std::string wkt("LINEARRING (-0.25 0.25, -0.25 0.75, -0.75 0.75, -0.75 0.25, -0.25 0.25)");
+
+    checkBuffer(wkt, 1, 0.1, 
+        "POLYGON ((0.73 0.05, 0.67 -0.13, 0.58 -0.31, 0.46 -0.46, 0.31 -0.58, 0.13 -0.67, -0.05 -0.73, -0.25 -0.75, -0.75 -0.75, -0.95 -0.73, -1.13 -0.67, -1.31 -0.58, -1.46 -0.46, -1.58 -0.31, -1.67 -0.13, -1.73 0.05, -1.75 0.25, -1.75 0.75, -1.73 0.95, -1.67 1.13, -1.58 1.31, -1.46 1.46, -1.31 1.58, -1.13 1.67, -0.95 1.73, -0.75 1.75, -0.25 1.75, -0.05 1.73, 0.13 1.67, 0.31 1.58, 0.46 1.46, 0.58 1.31, 0.67 1.13, 0.73 0.95, 0.75 0.75, 0.75 0.25, 0.73 0.05))");
+}
+
 } // namespace tut
diff --git a/tests/xmltester/tests/general/TestBuffer.xml b/tests/xmltester/tests/general/TestBuffer.xml
@@ -33,6 +33,57 @@
   </op></test>
 </case>
 
+<case>
+  <desc>
+    Closed Line
+  </desc>
+  <a>
+    LINESTRING (1 9, 9 9, 9 1, 1 1, 1 9)
+  </a>
+<test><op name='buffer' arg1='A' arg2='-1.0'>   POLYGON EMPTY  </op></test>
+<test><op name='buffer' arg1='A' arg2='0.0'>    POLYGON EMPTY  </op></test>
+<test><op name='buffer' arg1='A' arg2='1'>   
+POLYGON ((1 10, 9 10, 9.195090322016128 9.98078528040323, 9.38268343236509 9.923879532511286, 9.555570233019603 9.831469612302545, 9.707106781186548 9.707106781186548, 9.831469612302545 9.555570233019601, 9.923879532511286 9.38268343236509, 9.98078528040323 9.195090322016128, 10 9, 10 1, 9.98078528040323 0.8049096779838718, 9.923879532511286 0.6173165676349102, 9.831469612302545 0.4444297669803978, 9.707106781186548 0.2928932188134525, 9.555570233019603 0.1685303876974548, 9.38268343236509 0.0761204674887133, 9.195090322016128 0.0192147195967696, 9 0, 1 0, 0.8049096779838718 0.0192147195967696, 0.6173165676349103 0.0761204674887133, 0.444429766980398 0.1685303876974547, 0.2928932188134525 0.2928932188134524, 0.1685303876974547 0.4444297669803978, 0.0761204674887133 0.6173165676349102, 0.0192147195967696 0.8049096779838714, 0 1, 0 9, 0.0192147195967696 9.195090322016128, 0.0761204674887133 9.38268343236509, 0.1685303876974547 9.555570233019601, 0.2928932188134525 9.707106781186548, 0.444429766980398 9.831469612302545, 0.6173165676349103 9.923879532511286, 0.8049096779838718 9.98078528040323, 1 10), (2 8, 2 2, 8 2, 8 8, 2 8))
+  </op></test>
+<test><op name='buffer' arg1='A' arg2='10.0'>   
+POLYGON ((1 19, 9 19, 10.950903220161283 18.807852804032304, 12.826834323650898 18.238795325112868, 14.555702330196024 17.314696123025453, 16.071067811865476 16.071067811865476, 17.314696123025453 14.555702330196022, 18.238795325112868 12.826834323650898, 18.807852804032304 10.950903220161283, 19 9, 19 1, 18.807852804032304 -0.9509032201612824, 18.238795325112868 -2.826834323650898, 17.314696123025453 -4.555702330196022, 16.071067811865476 -6.071067811865475, 14.555702330196024 -7.314696123025453, 12.826834323650898 -8.238795325112868, 10.950903220161283 -8.807852804032304, 9 -9, 1 -9, -0.9509032201612819 -8.807852804032304, -2.826834323650897 -8.238795325112868, -4.55570233019602 -7.314696123025453, -6.071067811865475 -6.0710678118654755, -7.314696123025453 -4.555702330196022, -8.238795325112868 -2.826834323650899, -8.807852804032304 -0.9509032201612861, -9 1, -9 9, -8.807852804032304 10.950903220161287, -8.238795325112868 12.8268343236509, -7.314696123025453 14.555702330196022, -6.071067811865475 16.071067811865476, -4.55570233019602 17.314696123025453, -2.826834323650897 18.238795325112868, -0.9509032201612819 18.807852804032304, 1 19))
+  </op></test>
+</case>
+
+<case>
+  <desc>
+    Closed Line - CCW
+  </desc>
+  <a>
+    LINESTRING (1 9, 1 1, 9 1, 9 9, 1 9)
+  </a>
+<test><op name='buffer' arg1='A' arg2='-1.0'>   POLYGON EMPTY  </op></test>
+<test><op name='buffer' arg1='A' arg2='0.0'>    POLYGON EMPTY  </op></test>
+<test><op name='buffer' arg1='A' arg2='1'>   
+POLYGON ((1 10, 9 10, 9.195090322016128 9.98078528040323, 9.38268343236509 9.923879532511286, 9.555570233019603 9.831469612302545, 9.707106781186548 9.707106781186548, 9.831469612302545 9.555570233019601, 9.923879532511286 9.38268343236509, 9.98078528040323 9.195090322016128, 10 9, 10 1, 9.98078528040323 0.8049096779838718, 9.923879532511286 0.6173165676349102, 9.831469612302545 0.4444297669803978, 9.707106781186548 0.2928932188134525, 9.555570233019603 0.1685303876974548, 9.38268343236509 0.0761204674887133, 9.195090322016128 0.0192147195967696, 9 0, 1 0, 0.8049096779838718 0.0192147195967696, 0.6173165676349103 0.0761204674887133, 0.444429766980398 0.1685303876974547, 0.2928932188134525 0.2928932188134524, 0.1685303876974547 0.4444297669803978, 0.0761204674887133 0.6173165676349102, 0.0192147195967696 0.8049096779838714, 0 1, 0 9, 0.0192147195967696 9.195090322016128, 0.0761204674887133 9.38268343236509, 0.1685303876974547 9.555570233019601, 0.2928932188134525 9.707106781186548, 0.444429766980398 9.831469612302545, 0.6173165676349103 9.923879532511286, 0.8049096779838718 9.98078528040323, 1 10), (2 8, 2 2, 8 2, 8 8, 2 8))
+  </op></test>
+<test><op name='buffer' arg1='A' arg2='10.0'>   
+POLYGON ((1 19, 9 19, 10.950903220161283 18.807852804032304, 12.826834323650898 18.238795325112868, 14.555702330196024 17.314696123025453, 16.071067811865476 16.071067811865476, 17.314696123025453 14.555702330196022, 18.238795325112868 12.826834323650898, 18.807852804032304 10.950903220161283, 19 9, 19 1, 18.807852804032304 -0.9509032201612824, 18.238795325112868 -2.826834323650898, 17.314696123025453 -4.555702330196022, 16.071067811865476 -6.071067811865475, 14.555702330196024 -7.314696123025453, 12.826834323650898 -8.238795325112868, 10.950903220161283 -8.807852804032304, 9 -9, 1 -9, -0.9509032201612819 -8.807852804032304, -2.826834323650897 -8.238795325112868, -4.55570233019602 -7.314696123025453, -6.071067811865475 -6.0710678118654755, -7.314696123025453 -4.555702330196022, -8.238795325112868 -2.826834323650899, -8.807852804032304 -0.9509032201612861, -9 1, -9 9, -8.807852804032304 10.950903220161287, -8.238795325112868 12.8268343236509, -7.314696123025453 14.555702330196022, -6.071067811865475 16.071067811865476, -4.55570233019602 17.314696123025453, -2.826834323650897 18.238795325112868, -0.9509032201612819 18.807852804032304, 1 19))
+  </op></test>
+</case>
+
+<case>
+  <desc>
+    Linear Ring
+  </desc>
+  <a>
+    LINEARRING (1 9, 1 1, 9 1, 9 9, 1 9)
+  </a>
+<test><op name='buffer' arg1='A' arg2='-1.0'>   POLYGON EMPTY  </op></test>
+<test><op name='buffer' arg1='A' arg2='0.0'>    POLYGON EMPTY  </op></test>
+<test><op name='buffer' arg1='A' arg2='1'>   
+POLYGON ((1 10, 9 10, 9.195090322016128 9.98078528040323, 9.38268343236509 9.923879532511286, 9.555570233019603 9.831469612302545, 9.707106781186548 9.707106781186548, 9.831469612302545 9.555570233019601, 9.923879532511286 9.38268343236509, 9.98078528040323 9.195090322016128, 10 9, 10 1, 9.98078528040323 0.8049096779838718, 9.923879532511286 0.6173165676349102, 9.831469612302545 0.4444297669803978, 9.707106781186548 0.2928932188134525, 9.555570233019603 0.1685303876974548, 9.38268343236509 0.0761204674887133, 9.195090322016128 0.0192147195967696, 9 0, 1 0, 0.8049096779838718 0.0192147195967696, 0.6173165676349103 0.0761204674887133, 0.444429766980398 0.1685303876974547, 0.2928932188134525 0.2928932188134524, 0.1685303876974547 0.4444297669803978, 0.0761204674887133 0.6173165676349102, 0.0192147195967696 0.8049096779838714, 0 1, 0 9, 0.0192147195967696 9.195090322016128, 0.0761204674887133 9.38268343236509, 0.1685303876974547 9.555570233019601, 0.2928932188134525 9.707106781186548, 0.444429766980398 9.831469612302545, 0.6173165676349103 9.923879532511286, 0.8049096779838718 9.98078528040323, 1 10), (2 8, 2 2, 8 2, 8 8, 2 8))
+  </op></test>
+<test><op name='buffer' arg1='A' arg2='10.0'>   
+POLYGON ((1 19, 9 19, 10.950903220161283 18.807852804032304, 12.826834323650898 18.238795325112868, 14.555702330196024 17.314696123025453, 16.071067811865476 16.071067811865476, 17.314696123025453 14.555702330196022, 18.238795325112868 12.826834323650898, 18.807852804032304 10.950903220161283, 19 9, 19 1, 18.807852804032304 -0.9509032201612824, 18.238795325112868 -2.826834323650898, 17.314696123025453 -4.555702330196022, 16.071067811865476 -6.071067811865475, 14.555702330196024 -7.314696123025453, 12.826834323650898 -8.238795325112868, 10.950903220161283 -8.807852804032304, 9 -9, 1 -9, -0.9509032201612819 -8.807852804032304, -2.826834323650897 -8.238795325112868, -4.55570233019602 -7.314696123025453, -6.071067811865475 -6.0710678118654755, -7.314696123025453 -4.555702330196022, -8.238795325112868 -2.826834323650899, -8.807852804032304 -0.9509032201612861, -9 1, -9 9, -8.807852804032304 10.950903220161287, -8.238795325112868 12.8268343236509, -7.314696123025453 14.555702330196022, -6.071067811865475 16.071067811865476, -4.55570233019602 17.314696123025453, -2.826834323650897 18.238795325112868, -0.9509032201612819 18.807852804032304, 1 19))
+  </op></test>
+</case>
+
 <case>
   <desc>
   	Polygon