Merge pull request #1225 from ahocevar/closest-on-segment

squaredDistanceToSegment and footOfPerpendicularToSegment

src/ol/coordinate.js

@@ -42,6 +42,45 @@ ol.coordinate.add = function(coordinate, delta) {
 };
 
 
+/**
+ * Calculates the point closest to the passed coordinate on the passed segment.
+ * This is the foot of the perpendicular of the coordinate to the segment when
+ * the foot is on the segment, or the closest segment coordinate when the foot
+ * is outside the segment.
+ *
+ * @param {ol.Coordinate} coordinate The coordinate.
+ * @param {Array.<ol.Coordinate>} segment The two coordinates of the segment.
+ * @return {ol.Coordinate} The foot of the perpendicular of the coordinate to
+ *     the segment.
+ */
+ol.coordinate.closestOnSegment = function(coordinate, segment) {
+  var x0 = coordinate[0];
+  var y0 = coordinate[1];
+  var start = segment[0];
+  var end = segment[1];
+  var x1 = start[0];
+  var y1 = start[1];
+  var x2 = end[0];
+  var y2 = end[1];
+  var dx = x2 - x1;
+  var dy = y2 - y1;
+  var along = (dx == 0 && dy == 0) ? 0 :
+      ((dx * (x0 - x1)) + (dy * (y0 - y1))) / ((dx * dx + dy * dy) || 0);
+  var x, y;
+  if (along <= 0) {
+    x = x1;
+    y = y1;
+  } else if (along >= 1) {
+    x = x2;
+    y = y2;
+  } else {
+    x = x1 + along * dx;
+    y = y1 + along * dy;
+  }
+  return [x, y];
+};
+
+
 /**
  * @param {number=} opt_fractionDigits The number of digits to include
  *    after the decimal point. Default is `0`.
@@ -136,6 +175,19 @@ ol.coordinate.squaredDistance = function(coord1, coord2) {
 };
 
 
+/**
+ * Calculate the squared distance from a coordinate to a line segment.
+ *
+ * @param {ol.Coordinate} coordinate Coordinate of the point.
+ * @param {Array.<ol.Coordinate>} segment Line segment (2 coordinates).
+ * @return {number} Squared distance from the point to the line segment.
+ */
+ol.coordinate.squaredDistanceToSegment = function(coordinate, segment) {
+  return ol.coordinate.squaredDistance(coordinate,
+      ol.coordinate.closestOnSegment(coordinate, segment));
+};
+
+
 /**
  * @param {ol.Coordinate|undefined} coordinate Coordinate.
  * @return {string} Hemisphere, degrees, minutes and seconds.

src/ol/geom/base.js

@@ -1,31 +0,0 @@
-goog.provide('ol.geom');
-
-goog.require('ol.coordinate');
-
-
-/**
- * Calculate the squared distance from a point to a line segment.
- *
- * @param {ol.Coordinate} coordinate Coordinate of the point.
- * @param {Array.<ol.Coordinate>} segment Line segment (2 coordinates).
- * @return {number} Squared distance from the point to the line segment.
- */
-ol.geom.squaredDistanceToSegment = function(coordinate, segment) {
-  // http://de.softuses.com/103478, Kommentar #1
-  var v = segment[0];
-  var w = segment[1];
-  var l2 = ol.coordinate.squaredDistance(v, w);
-  if (l2 === 0) {
-    return ol.coordinate.squaredDistance(coordinate, v);
-  }
-  var t = ((coordinate[0] - v[0]) * (w[0] - v[0]) +
-      (coordinate[1] - v[1]) * (w[1] - v[1])) / l2;
-  if (t < 0) {
-    return ol.coordinate.squaredDistance(coordinate, v);
-  }
-  if (t > 1) {
-    return ol.coordinate.squaredDistance(coordinate, w);
-  }
-  return ol.coordinate.squaredDistance(coordinate,
-      [v[0] + t * (w[0] - v[0]), v[1] + t * (w[1] - v[1])]);
-};

src/ol/geom/linestring.js

@@ -3,8 +3,8 @@ goog.provide('ol.geom.LineString');
 goog.require('goog.asserts');
 goog.require('goog.events.EventType');
 goog.require('ol.CoordinateArray');
+goog.require('ol.coordinate');
 goog.require('ol.extent');
-goog.require('ol.geom');
 goog.require('ol.geom.Geometry');
 goog.require('ol.geom.GeometryEvent');
 goog.require('ol.geom.GeometryType');
@@ -104,7 +104,7 @@ ol.geom.LineString.prototype.distanceFromCoordinate = function(coordinate) {
   var coordinates = this.getCoordinates();
   var dist2 = Infinity;
   for (var i = 0, j = 1, len = coordinates.length; j < len; i = j++) {
-    dist2 = Math.min(dist2, ol.geom.squaredDistanceToSegment(coordinate,
+    dist2 = Math.min(dist2, ol.coordinate.squaredDistanceToSegment(coordinate,
         [coordinates[i], coordinates[j]]));
   }
   return Math.sqrt(dist2);

test/spec/ol/coordinate.test.js

@@ -0,0 +1,42 @@
+goog.provide('ol.test.coordinate');
+
+describe.only('ol.coordinate', function() {
+
+  describe('#closestOnSegment', function() {
+    it('can handle points where the foot of the perpendicular is closest',
+        function() {
+          var point = [2, 5];
+          var segment = [[-5, 0], [10, 0]];
+          expect(ol.coordinate.closestOnSegment(point, segment))
+              .to.eql([2, 0]);
+        });
+    it('can handle points where the foot of the perpendicular is not closest',
+        function() {
+          var point = [0, -6];
+          var segment = [[-5, 0], [0, -1]];
+          expect(ol.coordinate.closestOnSegment(point, segment))
+              .to.eql([0, -1]);
+        });
+  });
+
+  describe('#squaredDistanceToSegment', function() {
+    it('can handle points where the foot of the perpendicular is closest',
+        function() {
+          var point = [2, 5];
+          var segment = [[-5, 0], [10, 0]];
+          expect(ol.coordinate.squaredDistanceToSegment(point, segment))
+              .to.eql(25);
+        });
+    it('can handle points where the foot of the perpendicular is not closest',
+        function() {
+          var point = [0, -6];
+          var segment = [[-5, 0], [0, -1]];
+          expect(ol.coordinate.squaredDistanceToSegment(point, segment))
+              .to.eql(25);
+        });
+
+  });
+
+});
+
+goog.require('ol.coordinate');