Merge pull request #4541 from fredj/linestring_interpolated_point

Add new ol.geom.LineString#getCoordinateAt function

src/ol/geom/linestring.js

@@ -166,6 +166,23 @@ ol.geom.LineString.prototype.getCoordinates = function() {
 };
 
 
+/**
+ * Return the coordinate at the provided fraction along the linestring.
+ * The `fraction` is a number between 0 and 1, where 0 is the start of the
+ * linestring and 1 is the end.
+ * @param {number} fraction Fraction.
+ * @param {ol.Coordinate=} opt_dest Optional coordinate whose values will
+ *     be modified. If not provided, a new coordinate will be returned.
+ * @return {ol.Coordinate} Coordinate of the interpolated point.
+ * @api
+ */
+ol.geom.LineString.prototype.getCoordinateAt = function(fraction, opt_dest) {
+  return ol.geom.flat.interpolate.lineString(
+      this.flatCoordinates, 0, this.flatCoordinates.length, this.stride,
+      fraction, opt_dest);
+};
+
+
 /**
  * Return the length of the linestring on projected plane.
  * @return {number} Length (on projected plane).
@@ -182,9 +199,7 @@ ol.geom.LineString.prototype.getLength = function() {
  */
 ol.geom.LineString.prototype.getFlatMidpoint = function() {
   if (this.flatMidpointRevision_ != this.getRevision()) {
-    this.flatMidpoint_ = ol.geom.flat.interpolate.lineString(
-        this.flatCoordinates, 0, this.flatCoordinates.length, this.stride,
-        0.5, this.flatMidpoint_);
+    this.flatMidpoint_ = this.getCoordinateAt(0.5, this.flatMidpoint_);
     this.flatMidpointRevision_ = this.getRevision();
   }
   return this.flatMidpoint_;

test/spec/ol/geom/linestring.test.js

@@ -89,6 +89,22 @@ describe('ol.geom.LineString', function() {
 
     });
 
+    describe('#getCoordinateAt', function() {
+
+      it('return the first point when fraction is 0', function() {
+        expect(lineString.getCoordinateAt(0)).to.eql([1, 2]);
+      });
+
+      it('return the last point when fraction is 1', function() {
+        expect(lineString.getCoordinateAt(1)).to.eql([3, 4]);
+      });
+
+      it('return the mid point when fraction is 0.5', function() {
+        expect(lineString.getCoordinateAt(0.5)).to.eql([2, 3]);
+      });
+
+    });
+
   });
 
   describe('construct with 3D coordinates', function() {
@@ -320,6 +336,23 @@ describe('ol.geom.LineString', function() {
 
     });
 
+    describe('#getCoordinateAt', function() {
+
+      it('return the first point when fraction is 0', function() {
+        expect(lineString.getCoordinateAt(0)).to.eql([0, 0]);
+      });
+
+      it('return the last point when fraction is 1', function() {
+        expect(lineString.getCoordinateAt(1)).to.eql([7, 5]);
+      });
+
+      it('return the mid point when fraction is 0.5', function() {
+        var midpoint = lineString.getFlatMidpoint();
+        expect(lineString.getCoordinateAt(0.5)).to.eql(midpoint);
+      });
+
+    });
+
   });
 
   describe('with a simple XYM coordinates', function() {