How can I check whether a location is within a MapPolygon in the Silverlight Bing Maps control?

Question

I have a MapPolygon which covers a certain area on the Silverlight Bing Maps control, and I would like to know if a particular Location is located within this MapPolygon.

I have tried the following code which doesen't return the result I want because it only checks if the tested location is one of the vertices of the MapPolygon, and doesn't check if this Location is contained within this MapPolygon.

polygon.Locations.Contains(new Location(this.Site.Latitude, this.Site.Longitude, this.Site.Altitude));

Is it also possible to determine if two MapPolygons intersect one another?

Answer 1

Sure both of these things are fairly trivial, take a look at the following article. http://msdn.microsoft.com/en-us/library/cc451895.aspx It gives good methods for Bounding Box, Radius, and Polygon Search. Particularity take note of the pointInPolygon method.

Answer 2

The polygon.Locations is a list of points defining the polygon.

You have to make a method to find if your point is inside the polygon.

Use something like this (not tested if compiles):

static bool PointInPolygon(LocationCollection polyPoints, Location point)
{

    if (polyPoints.Length < 3)
    {
        return false;
    }

    bool inside = false;
    Location p1, p2;

    //iterate each side of the polygon
    Location oldPoint = polyPoints[polyPoints.Count - 1];

    foreach(Location newPoint in polyPoints)
    {
        //order points so p1.lat <= p2.lat;
        if (newPoint.Latitude > oldPoint.Latitude)
        {
            p1 = oldPoint;
            p2 = newPoint;
        }
        else
        {
            p1 = newPoint;
            p2 = oldPoint;
        }

        //test if the line is crossed and if so invert the inside flag.
        if ((newPoint.Latitude < point.Latitude) == (point.Latitude <= oldPoint.Latitude)
            && (point.Longitude - p1.Longitude) * (p2.Latitude - p1.Latitude)
             < (p2.Longitude - p1.Longitude) * (point.Latitude - p1.Latitude))
        {
            inside = !inside;
        }

        oldPoint = newPoint;
    }

    return inside;
}

And call it like this:

if (PointInPolygon(polygon.Locations, new Location(this.Site.Latitude, this.Site.Longitude, this.Site.Altitude)))
{
    //do something 
}