Add linear referencing methods to LineString

Author: jericks

doc/api/geom/linestring.rst

@@ -53,3 +53,33 @@ Methods
 
 Linestring geometries have the methods common to all :class:`geom.Geometry`
 subclasses.
+
+.. function:: LineString.interpolatePoint
+
+    :arg position: ``Number`` The position between 0 and 1.
+    :returns: :class:`geom.Point`
+
+    Returns a Point placed on the LineString at the given percentage along
+    the LineString.
+
+.. function:: LineString.locatePoint
+
+    :arg point: :class:`geom.Point` The Point
+    :returns: ``Number`` The position (0-1) or percentage of the Point along the LineString.
+
+    Returns a position or percentage between 0 and 1 of the Point along the LineString.
+
+.. function:: LineString.placePoint
+
+    :arg point: :class:`geom.Point` The Point.
+    :returns: :class:`geom.Point` The Point on the LineString.
+
+    Places or snaps the Point to the LineString.
+
+.. function:: LineString.subLine
+
+    :arg start: ``Number`` The start position between 0 and 1.
+    :arg end: ``Number`` The end position between 0 and 1.
+    :returns: :class:`geom.LineString` The sub LineString
+
+    Returns a position or percentage between 0 and 1 of the Point along the LineString.

src/main/java/org/geoscript/js/geom/LineString.java

@@ -12,6 +12,7 @@
 import org.mozilla.javascript.annotations.JSGetter;
 
 import com.vividsolutions.jts.geom.Coordinate;
+import com.vividsolutions.jts.linearref.LengthIndexedLine;
 
 public class LineString extends Geometry implements Wrapper {
 
@@ -112,6 +113,37 @@ public LineString reverse() {
         return (LineString) GeometryWrapper.wrap(getParentScope(), getGeometry().reverse());
     }
 
+    @JSFunction
+    public Point interpolatePoint(double position) {
+        LengthIndexedLine indexedLine = new LengthIndexedLine(this.getGeometry());
+        Coordinate c = indexedLine.extractPoint(position * getLength());
+        return new Point(getParentScope(), factory.createPoint(c));
+    }
+
+    @JSFunction
+    public double locatePoint(Point point) {
+        LengthIndexedLine indexedLine = new LengthIndexedLine(this.getGeometry());
+        double position = indexedLine.indexOf(point.getGeometry().getCoordinate());
+        double percentAlong = position / getLength();
+        return percentAlong;
+    }
+
+    @JSFunction
+    public Point placePoint(Point point) {
+        LengthIndexedLine indexedLine = new LengthIndexedLine(this.getGeometry());
+        double position = indexedLine.indexOf(point.getGeometry().getCoordinate());
+        Coordinate c = indexedLine.extractPoint(position);
+        return new Point(getParentScope(), factory.createPoint(c));
+    }
+
+    @JSFunction
+    public LineString subLine(double start, double end) {
+        LengthIndexedLine indexedLine = new LengthIndexedLine(this.getGeometry());
+        double length = getLength();
+        return new LineString(getParentScope(),
+                (com.vividsolutions.jts.geom.LineString) indexedLine.extractLine(start * length, end * length));
+    }
+
     /**
      * Returns underlying JTS geometry.
      */

src/test/resources/org/geoscript/js/tests/geoscript/geom/test_linestring.js

@@ -114,6 +114,62 @@ exports["test: centroid"] = function() {
 
 };
 
+exports["test: interpolatePoint"] = function() {
+    var line = new GEOM.LineString([
+        [1137466.548141059, 650434.9943107369],
+        [1175272.4129268457, 648011.541439853],
+        [1185935.6055587344, 632986.1336403737]
+    ]);
+
+    // Interpolate Point Start
+    var pt1 = line.interpolatePoint(0);
+    ASSERT.ok(pt1.equals(line.startPoint), "interpolate 0 should return start point");
+
+    // Interpolate Point Middle
+    var pt2 = line.interpolatePoint(0.5);
+    ASSERT.ok(pt2.equals(new GEOM.Point([1165562.9204493894, 648633.9448037925])), "interpolate 0.5 should return mid point");
+
+    // Interpolate Point End
+    var pt3 = line.interpolatePoint(1.0);
+    ASSERT.ok(pt3.equals(line.endPoint), "interpolate 1 should return end point");
+};
+
+exports["test: locatePoint"] = function() {
+    var line = new GEOM.LineString([
+        [1137466.548141059, 650434.9943107369],
+        [1175272.4129268457, 648011.541439853],
+        [1185935.6055587344, 632986.1336403737]
+    ]);
+    var point = new GEOM.Point([1153461.34, 649950.30]);
+    var position = line.locatePoint(point);
+    ASSERT.deepEqual(0.284, position.toFixed(3), "locate point position should be 0.284");
+};
+
+exports["test: placePoint"] = function() {
+    var line = new GEOM.LineString([
+        [1137466.548141059, 650434.9943107369],
+        [1175272.4129268457, 648011.541439853],
+        [1185935.6055587344, 632986.1336403737]
+    ]);
+    var point = new GEOM.Point([1153461.34, 649950.30]);
+    var placedPoint = line.placePoint(point) ;
+    ASSERT.ok(placedPoint.equals(new GEOM.Point([1153426.8271476042, 649411.899502625])),
+        "placed point should be POINT (1153426.8271476042 649411.899502625)");
+};
+
+exports["test: subLine"] = function() {
+    var line = new GEOM.LineString([
+        [1137466.548141059, 650434.9943107369],
+        [1175272.4129268457, 648011.541439853],
+        [1185935.6055587344, 632986.1336403737]
+    ]);
+    var subLine = line.subLine(0.33, 0.67);
+    ASSERT.ok(
+        new GEOM.LineString([[1156010.153864557, 649246.3016361536], [1175115.6870342216, 648021.5879714314]]).equals(subLine),
+        "subline should be LINESTRING (1156010.153864557 649246.3016361536, 1175115.6870342216 648021.5879714314)"
+    )
+};
+
 
 if (require.main == module.id) {
     system.exit(require("test").run(exports));