Map Your Apps: Listing 2.

Drawing an arc using a Bezier curve.

private void DrawCurve(Location start, Location finish)
{
  MapPolyline curve = new MapPolyline();
  curve.Stroke = new SolidColorBrush(Colors.Magenta);
  curve.StrokeThickness = 3.0;
  curve.StrokeDashArray = new DoubleCollection(new double[] { 5, 2 });
  curve.Opacity = 1.0;

  LocationCollection coll = new LocationCollection();

  // Compute control point
  Point p1 = myMap.LocationToViewportPoint(start);
  Point p2 = myMap.LocationToViewportPoint(finish);

  double boundingBoxHalfWidth = (p2.X - p1.X) / 2.0;
  double boundingBoxHalfHeight = (p1.Y - p2.Y) / 2.0;

  double centerX = (p1.X + p2.X) / 2.0;
  double centerY = (p1.Y + p2.Y) / 2.0;

  double xScale = 1.0;
  double yScale = 1.0;

  double controlX = centerX - (xScale * boundingBoxHalfWidth);
  double controlY = centerY - (yScale * boundingBoxHalfHeight);

  Point controlPt = new Point(controlX, controlY);
  Location controlLoc = myMap.ViewportPointToLocation(controlPt);

  // Compute intermediate Locations using the control point
  int numSegments = 31;
  doublet Delta = 1.0 / numSegments;
  for (double t = 0.0; t <= 1.0; t += tDelta) // Danger!
  {
    // x coordinate (longitudes)
    double a = (1.0 - t) * (1.0 - t) * start.Longitude;
    double b = 2.0 * (1.0 - t) * t * controlLoc.Longitude;
    double c = t * t * finish.Longitude;
    double Blon = a + b + c;

    // y coordinate (latitudes)
    a = (1.0 - t) * (1.0 - t) * start.Latitude;
    b = 2.0 * (1.0 - t) * t * controlLoc.Latitude;
    c = t * t * finish.Latitude;
    double Blat = a + b + c;

    coll.Add(new Location(Blat, Blon));
  }

  curve.Locations = coll;
  myMap.Children.Add(curve);
}

About the Author

Dr. James McCaffrey works for Microsoft Research in Redmond, Wash. He has worked on several Microsoft products including Azure and Bing. James can be reached at jamccaff@microsoft.com.

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