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, WA. James has worked on several key Microsoft products such as Internet Explorer and Bing. James can be reached at jamccaff@microsoft.com.