From f00cf3d5e63601b333d156fbe5f8136b44618d3e Mon Sep 17 00:00:00 2001
From: Martin Davis <mtnclimb@gmail.com>
Date: Tue, 4 Jun 2024 22:05:01 -0700
Subject: [PATCH] Simplify TopologyComputer logic

---
 .../operation/relateng/TopologyComputer.java  | 95 +++++++------------
 1 file changed, 34 insertions(+), 61 deletions(-)

diff --git a/modules/core/src/main/java/org/locationtech/jts/operation/relateng/TopologyComputer.java b/modules/core/src/main/java/org/locationtech/jts/operation/relateng/TopologyComputer.java
index de27064c94..b9e12fb927 100644
--- a/modules/core/src/main/java/org/locationtech/jts/operation/relateng/TopologyComputer.java
+++ b/modules/core/src/main/java/org/locationtech/jts/operation/relateng/TopologyComputer.java
@@ -180,72 +180,38 @@ private NodeSections getNodeSections(Coordinate nodePt) {
   
   public void addIntersection(NodeSection a, NodeSection b) {
     if (! a.isSameGeometry(b)) {
-      updateABIntersection(a, b);
+      updateIntersectionAB(a, b);
     }
-    //TODO: for self-intersections add virtual nodes to geometry components 
-
-    //-- add edges to node to allow full topology update later
+    //-- add edges to node to allow full topology evaluation later
     addNodeSections(a, b);
   }
-
-  private void addNodeSections(NodeSection ns0, NodeSection ns1) {
-    NodeSections sections = getNodeSections(ns0.nodePt());
-    sections.addNodeSection(ns0);
-    sections.addNodeSection(ns1);
-  }
-  
-  private void updateABIntersection(NodeSection a, NodeSection b) {
-    if (NodeSection.isProper(a, b)) {
-      updateABIntersectionProper(a, b);
-    }
-    else if (NodeSection.isAreaArea(a, b)) {
-      updateAreaAreaCross(a, b);
-    }
-    updateNodeLocation(a.nodePt(), a, b);
-  }
   
-  private void updateABIntersectionProper(NodeSection a, NodeSection b) {
-    int dimA = a.dimension();
-    int dimB = b.dimension();
-    if (dimA == 2 && dimB == 2) {
-      //- a proper edge intersection is an edge cross. 
+  /**
+   * Update topology for an intersection between A and B.
+   * 
+   * @param a the section for geometry A 
+   * @param b the section for geometry B
+   */
+  private void updateIntersectionAB(NodeSection a, NodeSection b) {
+    if (NodeSection.isAreaArea(a, b)) {
       updateAreaAreaCross(a, b);
     }
-    else if (dimA == 2 && dimB == 1) {
-      updateAreaLineCross(a, b);
-    }
-    else if (dimA == 1 && dimB == 2) {
-      updateAreaLineCross(b, a);
-    }
-    else if (dimA == 1 && dimB == 1) {
-      //-- nothing to do here - node topology is updated by caller
-    }
-    else {
-      Assert.shouldNeverReachHere(MSG_GEOMETRY_DIMENSION_UNEXPECTED);
-    }
-  }
-
-  private void updateAreaLineCross(NodeSection eArea, NodeSection eLine) {
-    //TODO: does this give any info apart from node? which is checked by caller
-    /**
-     * A proper crossing of a line and and area
-     * provides limited topological information,
-     * since the area edge intersection point
-     * may also be a node of a hole, or of another shell, or both.
-     * Full topology is determined when the node topology is evaluated.
-     */
-    boolean geomLine = eLine.isA();
-    Coordinate nodePt = eArea.nodePt();
-    int locLine = getGeometry(geomLine).locateNode(nodePt, eLine.getPolygonal());
-    int locArea = getGeometry(eArea.isA()).locateNode(nodePt, eArea.getPolygonal());
-    updateDim(eArea.isA(), locArea, locLine, Dimension.P);
+    updateNodeLocation(a, b);
   }
 
+  /**
+   * Updates topology for an AB Area-Area crossing node.
+   * Sections cross at a node if (a) the intersection is proper 
+   * (i.e. in the interior of two segments)
+   * or (b) if non-proper then whether the linework crosses
+   * is determined by the geometry of the segments on either side of the node.
+   * In these situations the area geometry interiors intersect (in dimension 2).
+   * 
+   * @param a the section for geometry A 
+   * @param b the section for geometry B
+   */
   private void updateAreaAreaCross(NodeSection a, NodeSection b) {
     boolean isProper = NodeSection.isProper(a, b);
-    /**
-     * A crossing of area edges determines that the interiors intersect.
-     */
     if (isProper || PolygonNodeTopology.isCrossing(a.nodePt(), 
         a.getVertex(0), a.getVertex(1), 
         b.getVertex(0), b.getVertex(1))) {
@@ -253,17 +219,24 @@ private void updateAreaAreaCross(NodeSection a, NodeSection b) {
     }
   }
   /**
-   * Adds a basic edge intersection point.
-   * @param pt
-   * @param b 
-   * @param a 
+   * Updates topology for a node at an AB edge intersection.
+   * 
+   * @param a the section for geometry A 
+   * @param b the section for geometry B
    */
-  private void updateNodeLocation(Coordinate pt, NodeSection a, NodeSection b) {
+  private void updateNodeLocation(NodeSection a, NodeSection b) {
+    Coordinate pt = a.nodePt();
     int locA = geomA.locateNode(pt, a.getPolygonal()); 
     int locB = geomB.locateNode(pt, b.getPolygonal()); 
     updateDim(locA, locB, Dimension.P);
   }
 
+  private void addNodeSections(NodeSection ns0, NodeSection ns1) {
+    NodeSections sections = getNodeSections(ns0.nodePt());
+    sections.addNodeSection(ns0);
+    sections.addNodeSection(ns1);
+  }
+  
   public void addPointOnPointInterior(Coordinate pt) {
     updateDim(Location.INTERIOR, Location.INTERIOR, Dimension.P); 
   }