Improve handling of detecting intersections across multiple rings

Author: rowanwins

CHANGELOG.md

@@ -1,3 +1,6 @@
+## 1.2.0
+- Improve handling of detecting intersections across multiple rings  
+
 ## 1.1.2
 - Fixed up some typos in the documentation.
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "sweepline-intersections",
-  "version": "1.1.2",
+  "version": "1.2.0",
   "description": "A module to check if a polygon self-intersects using a sweepline algorithm",
   "main": "dist/sweeplineIntersections.js",
   "module": "dist/sweeplineIntersections.esm.js",

src/Event.js

@@ -1,11 +1,12 @@
 
 export default class Event {
 
-    constructor (p) {
+    constructor (p, ringId) {
         this.p = {
             x: p[0],
             y: p[1]
         }
+        this.ringId = ringId
 
         this.otherEvent = null
         this.isLeftEndpoint = null

src/fillQueue.js

@@ -11,6 +11,8 @@ export default function fillEventQueue (geojson, eventQueue) {
         processFeature(geojson, eventQueue)
     }
 }
+
+let ringId = 0
 function processFeature (featureOrGeometry, eventQueue) {
     const geom = featureOrGeometry.type === 'Feature' ? featureOrGeometry.geometry : featureOrGeometry
     let coords = geom.coordinates
@@ -22,12 +24,12 @@ function processFeature (featureOrGeometry, eventQueue) {
         for (let ii = 0; ii < coords[i].length; ii++) {
             let currentP = coords[i][ii][0]
             let nextP = null
-
+            ringId = ringId + 1
             for (let iii = 0; iii < coords[i][ii].length - 1; iii++) {
                 nextP = coords[i][ii][iii + 1]
 
-                const e1 = new Event(currentP)
-                const e2 = new Event(nextP)
+                const e1 = new Event(currentP, ringId)
+                const e2 = new Event(nextP, ringId)
 
                 e1.otherEvent = e2
                 e2.otherEvent = e1

src/utils.js

@@ -5,10 +5,12 @@ export function areCoordsSame (p1, p2) {
 export function testSegmentIntersect (seg1, seg2) {
     if (seg1 === null || seg2 === null) return false
 
-    if (seg1.rightSweepEvent.isSamePoint(seg2.leftSweepEvent) ||
+    if (seg1.leftSweepEvent.ringId === seg2.leftSweepEvent.ringId &&
+        (seg1.rightSweepEvent.isSamePoint(seg2.leftSweepEvent) ||
+        seg1.rightSweepEvent.isSamePoint(seg2.leftSweepEvent) ||
         seg1.rightSweepEvent.isSamePoint(seg2.rightSweepEvent) ||
         seg1.leftSweepEvent.isSamePoint(seg2.leftSweepEvent) ||
-        seg1.leftSweepEvent.isSamePoint(seg2.rightSweepEvent)) return false
+        seg1.leftSweepEvent.isSamePoint(seg2.rightSweepEvent))) return false
 
     const x1 = seg1.leftSweepEvent.p.x
     const y1 = seg1.leftSweepEvent.p.y

test/fixtures/notSimple/chileKinked.geojson

@@ -0,0 +1,19 @@
+{
+      "type": "Feature",
+      "properties": {
+        "expectedIntersections": 3
+      },
+      "geometry": {
+        "type": "MultiLineString",
+        "coordinates": [[
+            [7, 50],
+            [8, 50],
+            [9, 50]
+        ],
+        [
+            [8, 49],
+            [8, 50],
+            [8, 51]
+        ]]
+      }
+}

test/fixtures/notSimple/itersect-shared-vertice.geojson

@@ -0,0 +1,23 @@
+    {
+      "type": "Feature",
+      "properties": {
+        "expectedIntersections": 2
+      },
+      "geometry": {
+        "type": "MultiLineString",
+        "coordinates": [[
+          [120, -20],
+          [122.5, -16],
+          [125, -15],
+          [127.5, -16],
+          [130, -20]
+        ],[
+          [120, -20],
+          [122.5, -24],
+          [125, -25],
+          [127.5, -24],
+          [130, -20]
+        ]
+        ]
+      }
+    }