Fixes bug when collinear points sharing the same polar angle get being passed through to the resultant hull array, when they should be being removed. closes #7

brian3kb · brian3kb · commit 11af13bc8e0a · 2015-12-17T23:42:52.000Z
diff --git a/bower.json b/bower.json
@@ -1,6 +1,6 @@
 {
   "name": "graham_scan",
-  "version": "1.0.2",
+  "version": "1.0.3",
   "main": "graham_scan.min.js",
   "license": "MIT",
   "ignore": [
diff --git a/example/app1.js b/example/app1.js
@@ -15,6 +15,7 @@ function initialize() {
         {'lat' : '48.9167', 'lon' : '11.3'},
         {'lat' : '48.8333', 'lon' : '11.4167'},
         {'lat' : '48.8667', 'lon' : '11.0667'},
+        {'lat' : '48.7667', 'lon' : '11.0667'},
         {'lat' : '48.893175', 'lon' : '10.990565'},
         {'lat' : '48.8833', 'lon' : '11'},
         {'lat' : '48.8', 'lon' : '11.1'},
diff --git a/example/app2.js b/example/app2.js
@@ -153,6 +153,7 @@ function initialize() {
 
         //Convert to google latlng objects
         hullPoints = hullPoints.map(function (item) {
+            console.log('x:'+item.x + ', y:' + item.y);
             return new google.maps.LatLng(item.y, item.x);
         });
 
diff --git a/example/app5.js b/example/app5.js
@@ -0,0 +1,45 @@
+(function() {
+    var canvas = document.getElementById('hullCanvas'),
+        ctx = canvas.getContext('2d'),
+        convexHull = new ConvexHullGrahamScan(),
+        points = [
+            [2,2], [2,-2], [-2,-2], [-2,2],
+            [3,3], [3,-3], [-3,-3], [-3,3],
+            [4,4], [4,-4], [-4,-4], [-4,4],
+            [5,5], [5,-5], [-5,-5], [-5,5]
+        ],
+        hull,
+        drawPoint = function(point, fill) {
+            ctx.beginPath();
+            ctx.arc((point.x*20)+200, (point.y*20)+200, 3, 0, 3* Math.PI);
+            if (fill){
+                ctx.fillStyle = fill;
+                ctx.fill();
+            } else {
+                ctx.stroke();
+            }
+        };
+
+    points.forEach(function(p) {
+        convexHull.addPoint(p[0], p[1]);
+        drawPoint({x:p[0], y:p[1]});
+    });
+
+    hull = convexHull.getHull();
+    console.log(hull);
+
+    ctx.beginPath();
+    ctx.moveTo((hull[0].x*20)+200, (hull[0].y*20)+200);
+    hull.forEach(function(p) {
+        ctx.lineTo((p.x*20)+200, (p.y*20)+200);
+    });
+    ctx.lineTo((hull[0].x*20)+200, (hull[0].y*20)+200);
+    ctx.stroke();
+    ctx.closePath();
+
+    hull.forEach(function(p) {
+        drawPoint(p, 'green');
+    });
+
+
+})();
diff --git a/example/canvas_example5.html b/example/canvas_example5.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta name="viewport" content="initial-scale=1.0, user-scalable=no">
+    <meta charset="utf-8">
+    <title>Graham's Scan Canvas Example</title>
+
+    <link href="main.css" rel="stylesheet">
+</head>
+<body>
+<canvas id="hullCanvas" height="800" width="800"></canvas>
+</body>
+<script src="../src/graham_scan.js"></script>
+<script src="app5.js"></script>
+
+</html>
diff --git a/graham_scan.min.js b/graham_scan.min.js
diff --git a/package.json b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "graham_scan",
-  "version": "1.0.2",
+  "version": "1.0.3",
   "description": "Implementation of the Graham Scan algorithm to calculate a convex hull from a given array of x, y coordinates.",
   "license": "MIT",
   "directories": {
diff --git a/src/graham_scan.js b/src/graham_scan.js
@@ -1,8 +1,8 @@
 /**
  * Graham's Scan Convex Hull Algorithm
- * @desc An implementation of the Graham's Scan Convex Hull algorithm in Javascript.
+ * @desc An implementation of the Graham's Scan Convex Hull algorithm in JavaScript.
  * @author Brian Barnett, brian@3kb.co.uk, http://brianbar.net/ || http://3kb.co.uk/
- * @version 1.0.2
+ * @version 1.0.3
  */
 function ConvexHullGrahamScan() {
     this.anchorPoint = undefined;
@@ -48,12 +48,15 @@ ConvexHullGrahamScan.prototype = {
         if (this.anchorPoint === undefined) {
             //Create new anchorPoint.
             this.anchorPoint = new this.Point(x, y);
-
+            return;
             // Sets anchorPoint if point being added is further left.
-        } else if (this.anchorPoint.y > y || (this.anchorPoint.y == y && this.anchorPoint.x > x)) {
-            this.anchorPoint.y = y;
-            this.anchorPoint.x = x;
-            this.points.unshift(new this.Point(x, y));
+        } else if (
+            (this.anchorPoint.y > y && this.anchorPoint.x > x) ||
+            (this.anchorPoint.y === y && this.anchorPoint.x > x) ||
+            (this.anchorPoint.y > y && this.anchorPoint.x === x)
+        ) {
+            this.points.push(new this.Point(this.anchorPoint.x, this.anchorPoint.y));
+            this.anchorPoint = new this.Point(x, y);
             return;
         }
 
@@ -97,7 +100,7 @@ ConvexHullGrahamScan.prototype = {
 
         }
 
-        return false;
+        return true;
     },
 
     getHull: function () {
@@ -114,6 +117,7 @@ ConvexHullGrahamScan.prototype = {
 
         //If there are less than 4 points, joining these points creates a correct hull.
         if (pointsLength < 4) {
+            points.unshift(this.anchorPoint);
             return points;
         }
 
@@ -138,6 +142,13 @@ ConvexHullGrahamScan.prototype = {
 
             if (points.length == 0) {
                 if (pointsLength == hullPoints.length) {
+                    //check for duplicate anchorPoint edge-case, if not found, add the anchorpoint as the first item.
+                    var ap = this.anchorPoint;
+                    if (!hullPoints.some(function(p){
+                            return(p.x == ap.x && p.y == ap.y);
+                        })) {
+                        hullPoints.unshift(this.anchorPoint);
+                    }
                     return hullPoints;
                 }
                 points = hullPoints;
diff --git a/test/graham_scan.Test.js b/test/graham_scan.Test.js
@@ -4,12 +4,12 @@ test('Add a single new point',2 , function() {
     var testGSHull = new ConvexHullGrahamScan();
 
     testGSHull.addPoint(11, 50);
-    console.log(testGSHull.points[0]);
+    console.log(testGSHull.anchorPoint);
     console.log(new testGSHull.Point(11, 50));
-    equal(testGSHull.points[0], new testGSHull.Point(11, 50),
+    equal(testGSHull.anchorPoint, new testGSHull.Point(11, 50),
         'Tests a point has been added to the points array correctly.');
     testGSHull.addPoint(10, 50);
-    equal(testGSHull.points[0], new testGSHull.Point(10, 50),
+    equal(testGSHull.anchorPoint, new testGSHull.Point(10, 50),
         'Tests that same y value then checks x value for comparison.');
 });
 
@@ -63,8 +63,8 @@ test('Polar angle point comparison check.',3, function(){
         'Check if last point added results in a concave.');
 
     equal(testGSHull._checkPoints( {'y' : '48.1', 'x' : '11.1'},
-                                   {'y' : '48.1', 'x' : '11.1'},
-                                   {'y' : '48.1', 'x' : '11.1'}),
+                                   {'y' : '48.1', 'x' : '-11.1'},
+                                   {'y' : '-48.1', 'x' : '11.1'}),
         false,
         'Check if last point added results in a concave.');
 });
@@ -133,9 +133,40 @@ test('Test handling 4 points rectangular.',1, function(){
     testGSHull.anchorPoint = {'y':50.157913235507706,'x':29.900512524414125};
     testGSHull.points = [
         {'y' : '50.157913235507706', 'x' : '29.900512524414125'},
+        {'y' : '50.15791323550770611', 'x' : '31.146087475586'},
         {'y' : '50.74029471119741', 'x' : '31.146087475586'},
-        {'y' : '50.74029471119741', 'x' : '29.900512524414125'},
-        {'y' : '50.15791323550770611', 'x' : '31.146087475586'}
+        {'y' : '50.74029471119741', 'x' : '29.900512524414125'}
+    ];
+
+    equal(testGSHull.getHull(), expectedHull, 'Check output hull is as expected.');
+});
+
+test('that collinear points sharing the same polar angle are removed from resultant hull.',1, function(){
+    var expectedHull = [
+        {'y':-5,'x':-5},
+        {'y':-5,'x':5},
+        {'y':5,'x':5},
+        {'y':5,'x':-5}
+    ];
+    var testGSHull = new ConvexHullGrahamScan();
+    testGSHull.anchorPoint = {'y':-5,'x':-5};
+    testGSHull.points = [
+        {'y' : '2', 'x' : '2'},
+        {'y' : '-2', 'x' : '2'},
+        {'y' : '-2', 'x' : '-2'},
+        {'y' : '2', 'x' : '-2'},
+        {'y' : '3', 'x' : '3'},
+        {'y' : '-3', 'x' : '3'},
+        {'y' : '-3', 'x' : '-3'},
+        {'y' : '3', 'x' : '-3'},
+        {'y' : '4', 'x' : '4'},
+        {'y' : '-4', 'x' : '4'},
+        {'y' : '-4', 'x' : '-4'},
+        {'y' : '4', 'x' : '-4'},
+        {'y' : '5', 'x' : '5'},
+        {'y' : '-5', 'x' : '5'},
+        {'y' : '-5', 'x' : '-5'},
+        {'y' : '5', 'x' : '-5'}
     ];
 
     equal(testGSHull.getHull(), expectedHull, 'Check output hull is as expected.');

Original file line number	Diff line number	Diff line change
`@@ -1,6 +1,6 @@`
`1`	`1`	`{`
`2`	`2`	`"name": "graham_scan",`
`3`		`- "version": "1.0.2",`
	`3`	`+ "version": "1.0.3",`
`4`	`4`	`"main": "graham_scan.min.js",`
`5`	`5`	`"license": "MIT",`
`6`	`6`	`"ignore": [`