根据视口中的标题计算纬度和经度

Question

Does anyone have a solution for calculating the Latitude and Longitude corners of a view based on heading?

I have a function that calculates the LatLng corners of a view if heading is 0. But I wish to find a way to calculate the corners based on a new heading, if the user spins the map for example.

The code I have now that does this with Heading = 0 is this.

public GeoboundingBox GetBounds(MapControl map)
    {
        if(map.Center.Position.Latitude == 0) { return default(GeoboundingBox); }

        /*
         * resolution m/px = 15653.04 m/px * Cos(LatInRad) / 2^zoomLevel
         * 111325 m/deg
         */

        double latInRad = Math.Cos(map.Center.Position.Latitude * Math.PI / 180);
        double lngInRad = Math.Cos(map.Center.Position.Longitude * Math.PI / 180);

        double degreePerPixel = (156543.04 * latInRad * lngInRad) / (111325 * Math.Pow(2, map.ZoomLevel));

        double mHalfWidthInDegrees = map.ActualWidth * degreePerPixel / 0.89;
        double mHalfHeightInDegrees = map.ActualHeight * degreePerPixel / 1.65;

        double mNorth = map.Center.Position.Latitude + mHalfHeightInDegrees;
        double mWest = map.Center.Position.Longitude - mHalfWidthInDegrees;
        double mSouth = map.Center.Position.Latitude - mHalfHeightInDegrees;
        double mEast = map.Center.Position.Longitude + mHalfWidthInDegrees;

        GeoboundingBox mBounds = new GeoboundingBox(
            new BasicGeoposition()
            {
                Latitude = mNorth,
                Longitude = mWest
            },
            new BasicGeoposition()
            {
                Latitude = mSouth,
                Longitude = mEast
            });
      return mBounds;
 }

Answer 1

The simplest solution to get the bounding box of the visible map area is to get the values directly from the map control.

For the built-in Map control by Microsoft you have the MapControl.GetLocationFromOffset method which takes a Point relative to the control and returns the geographic location at that point.

mapControl.GetLocationFromOffset(
   new Point(0, 0),
   out upperLeftGeoPoint
);
mapControl.GetLocationFromOffset (
   new Point( mapControl.ActualWidth, 0 ), 
   out upperRightGeoPoint
);
mapControl.GetLocationFromOffset (
   new Point( 0, mapControl.ActualHeight ), 
   out bottomLeftGeoPoint
);
mapControl.GetLocationFromOffset (
   new Point( mapControl.ActualWidth, mapControl.ActualHeight ), 
   out bottomRightGeoPoint
);

Be aware that the method will throw an exception in case the point is outside the range of the map control.

In your case, you will need to get the values for all four corners, because it the map is rotated.

For more documentation of this method, see MSDN .

If you are using the third-party XAML Map Control, you have the equivalent ViewportPointToLocation method

var northWestCorner = mapControl.ViewportPointToLocation( 
   new Point( 0, 0 )
);
var southEastCorner = mapControl.ViewportPointToLocation(
   new Point( mapControl.ActualWidth, mapControl.ActualHeight )
);
//analogous for north east, south west

Answer 2

It looks like you are trying to calculate the bounding box of the map. Using degree per pixel won't work as this value changes with the latitude value. Instead take a look at the solution here on how to calculate the bounding box of a map in WP8.1 (this basis to the Win10 map control) Get view bounds of a Map