Bing Maps Silverlight Control Part 5: Calculating Distance

My dad was the first person to show me how to measure distances on a map using a pair of dividers and the scale printed on the map key. There is a much better way to do this using the Bing Maps Silverlight control -- it just takes a little programming and finding the right equation.



Here is the Bobcat Video I told you about:



Back to Programming...

Here is how you calculate the distance between points on the earth. You also need to know EarthRadiusInMiles = 3956.0;

        /// <summary> 
        /// Calculate the distance between two geocodes. Defaults to using Miles. 
        /// </summary> 
        public static double CalcDistance(double lat1, double lng1, double lat2, double lng2)
        {
            return CalcDistance(lat1, lng1, lat2, lng2, GeoCodeCalcMeasurement.Miles);
        }
        /// <summary> 
        /// Calculate the distance between two geocodes. 
        /// </summary> 
        public static double CalcDistance(double lat1, double lng1, double lat2, double lng2, GeoCodeCalcMeasurement m)
        {
            double radius = GeoCodeCalc.EarthRadiusInMiles;
            if (m == GeoCodeCalcMeasurement.Kilometers) { radius = GeoCodeCalc.EarthRadiusInKilometers; }
            return radius * 2 * Math.Asin(Math.Min(1, Math.Sqrt((Math.Pow(Math.Sin((DiffRadian(lat1, lat2)) / 2.0), 2.0) + Math.Cos(ToRadian(lat1)) * Math.Cos(ToRadian(lat2)) * Math.Pow(Math.Sin((DiffRadian(lng1, lng2)) / 2.0), 2.0)))));
        }

I created a Marker class to mark the end points of the distance calculation. To show the user that they are in distance calculation mode, I have also changed the cursor on the map control. In this case, I alternate between the arrow and the pointing finger.

        PointsOfInterest m_oMarkers = new PointsOfInterest();

        void cbMeasure_Checked(object sender, RoutedEventArgs e)
        {
            Map1.Cursor = Cursors.Hand;
            m_oMarkers.Clear();
        }
        void cbMeasure_Unchecked(object sender, RoutedEventArgs e)
        {
            Map1.Cursor = Cursors.Arrow;
            if ( m_oMarkers.Count > 1 )
                AddLine(m_oMarkers,.5);
        }

The code for collecting the user's selection of points is here:

        void Map1_MouseClick(object sender, MapMouseEventArgs e)
        {
            var oLocation = Map1.ViewportPointToLocation(e.ViewportPoint);

            PointOfInterest oPOI = null;
            if (cbMeasure.IsChecked == true)
            {
                oPOI = new Marker() { Loc = oLocation };
                m_oMarkers.Add(oPOI);
            }
            else
            {
                oPOI = new PointOfInterest() { Loc = oLocation };
                m_oList.Add(oPOI);
            }
           
            RenderPoint(oPOI);

            if (cbDraw.IsChecked == true)
                try
                {
                    double dRadius = double.Parse(txtRadius.Text);
                    AddCircle(oLocation, dRadius, .5);
                }
                catch( Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }
        }

Using a polyline and a tool tip is great way to report the distance:

       double DistanceInMiles(LocationCollection oLocs)
        {
            double dDistance = 0.0;
            for (int i = 0; i < oLocs.Count() - 1; i++)
                dDistance += DistanceInMiles(oLocs[i], oLocs[i + 1]);

            return dDistance;
        }

        double DistanceInMiles(Location Loc1, Location Loc2)
        {
            double dMiles = GeoCodeCalc.CalcDistance(Loc1.Latitude, Loc1.Longitude, Loc2.Latitude, Loc2.Longitude);
            return dMiles;
        }

        LocationCollection RenderLine(List<PointOfInterest> oList)
        {

            var oPOIs = (from oPOI in oList
                         where oPOI is Marker
                         select oPOI).ToList<PointOfInterest>();

            var oLocs = new LocationCollection();
            foreach (var oPOI in oPOIs)
                oLocs.Add(oPOI.Loc);

            return oLocs;
        }


        void AddLine(List<PointOfInterest> oList, double dOpacity)
        {
            MapPolyline polyline = new MapPolyline();
            polyline.Stroke = new SolidColorBrush(Colors.Red);
            polyline.StrokeThickness = 1;
            polyline.Opacity = dOpacity;

            //this works in miles
            LocationCollection oLocs = RenderLine(oList);
            polyline.Locations = oLocs;
            Map1.AddChild(polyline);

            double dDist = DistanceInMiles(oLocs);

            ToolTipService.SetToolTip(polyline, string.Format("{0:0.0} mi \n {1:0.00} yd", dDist, dDist * 5280.0 / 3.0));
        }