Add linear referencing methods to linestring

geoscript/geom/linestring.py

@@ -1,6 +1,8 @@
 from com.vividsolutions.jts.geom import Coordinate
 from com.vividsolutions.jts.geom import LineString as _LineString
+from com.vividsolutions.jts.linearref import LengthIndexedLine
 from geoscript import core
+from geoscript.geom import Point
 import geom
 
 class LineString(_LineString):
@@ -27,5 +29,56 @@ def __init__(self, *coords):
 
     _LineString.__init__(self, ls.coordinateSequence, geom._factory)
 
+  def interpolatePoint(self, position):
+      """
+      Interpolate a :class:`Point <geoscript.geom.Point>` on the :class:`LineString <geoscript.geom.LineString>` at the given position from 0 to 1.
+
+      *position* is number between 0 and 1
+
+      """
+      indexedLine = LengthIndexedLine(self) 
+      length = self.getLength()
+      coordinate = indexedLine.extractPoint(position * length)
+      return Point(coordinate.x, coordinate.y)
+
+  def locatePoint(self, *coord):
+      """
+      Locate the position of the :class:`point <geoscript.geom.Point>` along this :class:`LineString <geoscript.geom.LineString>`. The position returned is a number between 0 and 1.
+
+      *coord* A :class:`Point <geoscript.geom.Point>` or a variable list of x,y,z arguments.
+
+      """
+      point = coord[0] if isinstance(coord[0], Point) else Point(*coord)
+      indexedLine = LengthIndexedLine(self)
+      position = indexedLine.indexOf(point.coordinate)
+      percentAlong = position / self.getLength()
+      return percentAlong
+
+  def placePoint(self, *coord):
+      """
+      Place or snap the :class:`point <geoscript.geom.Point>` to the `LineString <geoscript.geom.LineString>`. This method returns a new placed `Point <geoscript.geom.Point>`.
+
+      *coord* A :class:`Point <geoscript.geom.Point>` or a variable list of x,y,z arguments.
+
+      """
+      point = coord[0] if isinstance(coord[0], Point) else Point(*coord)
+      indexedLine = LengthIndexedLine(self)
+      position = indexedLine.indexOf(point.coordinate)
+      coord = indexedLine.extractPoint(position)
+      return Point(coord.x, coord.y)
+
+  def subLine(self, start, end):
+      """
+      Extract a sub :class:`LineString <geoscript.geom.LineString>` using a start and end position.  Both positions are numbers between 0 and 1.  A new :class:`LineString <geoscript.geom.LineString>` is returned.
+
+      *start* The start position between 0 and 1
+
+      *end* The end position between 0 and 1
+
+      """
+      indexedLine = LengthIndexedLine(self)
+      length = self.getLength()
+      return LineString(indexedLine.extractLine(start * length, end * length))
+
 geom._enhance(LineString)
 core.registerTypeMapping(_LineString, LineString)

tests/test_geom.py

@@ -174,3 +174,57 @@ def testWriteGML(self):
 
     poly = geom.Polygon([[1,2],[3,4],[5,6],[1,2]])
     assert str(poly) == str(geom.readGML(geom.writeGML(poly,ver=3.2),ver=3.2)) 
+
+  def testInterpolatePoint(self):
+    line = geom.LineString(
+        (1137466.548141059, 650434.9943107369),
+        (1175272.4129268457, 648011.541439853),
+        (1185935.6055587344, 632986.1336403737)
+    )
+
+    # start
+    point1 = line.interpolatePoint(0)
+    assert str(line.startPoint) == str(point1)
+
+    # middle
+    point2 = line.interpolatePoint(0.5)
+    assert "POINT (1165562.9204493894 648633.9448037925)" == str(point2)
+
+    # end
+    point3 = line.interpolatePoint(1.0)
+    assert str(line.endPoint) == str(point3)
+
+  def testLocatePoint(self):
+    line = geom.LineString(
+        (1137466.548141059, 650434.9943107369),
+        (1175272.4129268457, 648011.541439853),
+        (1185935.6055587344, 632986.1336403737)
+    )
+    point = geom.Point(1153461.34, 649950.30)
+    position = line.locatePoint(point)
+    self.assertAlmostEqual(0.284, position, places=3)
+    position = line.locatePoint(1153461.34, 649950.30)
+    self.assertAlmostEqual(0.284, position, places=3)
+
+  def testPlacePoint(self):
+    line = geom.LineString(
+        (1137466.548141059, 650434.9943107369),
+        (1175272.4129268457, 648011.541439853),
+        (1185935.6055587344, 632986.1336403737)
+    )
+    point1 = geom.Point(1153461.34, 649950.30)
+    point2 = line.placePoint(point1)
+    assert "POINT (1153426.8271476042 649411.899502625)" == str(point2)
+    point3 = line.placePoint(1153461.34, 649950.30)
+    assert "POINT (1153426.8271476042 649411.899502625)" == str(point3)
+
+  def testSubLine(self):
+    line = geom.LineString(
+        (1137466.548141059, 650434.9943107369),
+        (1175272.4129268457, 648011.541439853),
+        (1185935.6055587344, 632986.1336403737)
+    )
+    subLine = line.subLine(0.33, 0.67)
+    assert "LINESTRING (1156010.153864557 649246.3016361536, 1175115.6870342216 648021.5879714314)" == str(subLine)
+
+