获取地图的视图边界

Question

I'm developing a Windows Phone 8.1 app that works with Bing Maps. During the rendering of this map I use the TrySetViewBoundsAsync to set correctly my custom view. But now I want to get this information (after the user changes the view by zooming/moving the map) but I don't find any method that helps me.

How can I get the view bounds?

Answer 1

There isn't a built in method for this, however it can be done fairly easily. Here is a bit of code for this which I pulled from the Microsoft Maps Spatial Toolbox project :

public static GeoboundingBox GetBounds(this MapControl map)
{
    Geopoint topLeft = null;

    try
    {
        map.GetLocationFromOffset(new Windows.Foundation.Point(0, 0), out topLeft);
    }
    catch
    {
        var topOfMap = new Geopoint(new BasicGeoposition()
        {
            Latitude = 85,
            Longitude = 0
        });

        Windows.Foundation.Point topPoint;
        map.GetOffsetFromLocation(topOfMap, out topPoint);
        map.GetLocationFromOffset(new Windows.Foundation.Point(0, topPoint.Y), out topLeft);
    }

    Geopoint bottomRight = null;
    try
    {
        map.GetLocationFromOffset(new Windows.Foundation.Point(map.ActualWidth, map.ActualHeight), out bottomRight);
    }
    catch
    {
        var bottomOfMap = new Geopoint(new BasicGeoposition()
        {
            Latitude = -85,
            Longitude = 0
        });

        Windows.Foundation.Point bottomPoint;
        map.GetOffsetFromLocation(bottomOfMap, out bottomPoint);
        map.GetLocationFromOffset(new Windows.Foundation.Point(0, bottomPoint.Y), out bottomRight);
    }

    if (topLeft != null && bottomRight != null)
    {
        return new GeoboundingBox(topLeft.Position, bottomRight.Position);
    }

    return null;
}

Answer 2

Note that rbrundritt's solution will not work for oblique (tilted) views. In that case, the visible region resembles more an inverted trapezoid than a bounding box. Also the top-left corner might not be a valid location if the horizon is visible.

For Windows 10 Anniversary Update (version 1607), the MapControl supports a new method GetVisibleRegion() to help you with this.

The following should return you the view bounds of the map:

map.GetVisibleRegion(MapVisibleRegionKind.Full)

See the MapControl documentation for more details.