How can I determine if a geopoint is displayed in currently viewable area?

Question

Say I have mapview control in my Android app. If I know a landmark exists at a certain latitude and longitude, how can I determine if that landmark is currently viewable on the user's screen? Is there a method for getting the coordinates for the top left and bottom right corners of the visible area?

Answer 1

You can project GeoPoint to Point and check if it is box (0, screen width) by (0, screen height)

See: https://developer.android.com/reference/com/google/android/gms/maps/Projection.html

Answer 2

Something like this will do the trick.

private boolean isCurrentLocationVisible()
    {
        Rect currentMapBoundsRect = new Rect();
        Point currentDevicePosition = new Point();
        GeoPoint deviceLocation = new GeoPoint((int) (bestCurrentLocation.getLatitude() * 1000000.0), (int) (bestCurrentLocation.getLongitude() * 1000000.0));

        mapView.getProjection().toPixels(deviceLocation, currentDevicePosition);
        mapView.getDrawingRect(currentMapBoundsRect);

        return currentMapBoundsRect.contains(currentDevicePosition.x, currentDevicePosition.y);

    }

Answer 3

Joining the tips here, here and here:

Here is the complete code of my CustomMapView:

package net.alouw.alouwCheckin.ui.map;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Pair;
import com.google.android.maps.GeoPoint;
import com.google.android.maps.MapView;

/**
 * @author Felipe Micaroni Lalli (micaroni@gmail.com)
 */
public class CustomMapView extends MapView {  
    public CustomMapView(Context context, String s) {
        super(context, s);
    }

    public CustomMapView(Context context, AttributeSet attributeSet) {
        super(context, attributeSet);
    }

    public CustomMapView(Context context, AttributeSet attributeSet, int i) {
        super(context, attributeSet, i);
    }

    /**
     *
     * @return a Pair of two pairs with: top right corner (lat, lon), bottom left corner (lat, lon)
     */
    public Pair<Pair<Double, Double>, Pair<Double, Double>> getMapCorners() {
        GeoPoint center = getMapCenter();
        int latitudeSpan = getLatitudeSpan();
        int longtitudeSpan = getLongitudeSpan();

        double topRightLat = (center.getLatitudeE6() + (latitudeSpan / 2.0d)) / 1.0E6;
        double topRightLon = (center.getLongitudeE6() + (longtitudeSpan / 2.0d)) / 1.0E6;

        double bottomLeftLat = (center.getLatitudeE6() - (latitudeSpan / 2.0d)) / 1.0E6;
        double bottomLeftLon = (center.getLongitudeE6() - (longtitudeSpan / 2.0d)) / 1.0E6;

        return new Pair<Pair<Double, Double>, Pair<Double, Double>>(
                new Pair<Double, Double>(topRightLat, topRightLon),
                new Pair<Double, Double>(bottomLeftLat, bottomLeftLon));
    }
}

Answer 4

Ok since it took me some time now to find a simple working solution I will post it here for all after me ;) In your own subclass of MapView just use the following:

GeoPoint topLeft = this.getProjection().fromPixels(0, 0);
GeoPoint bottomRight = this.getProjection().fromPixels(getWidth(),getHeight());

Thats all, then you can get the coordinates via

topLeft.getLatitudeE6() / 1E6
topLeft.getLongitudeE6() / 1E6

and

bottomRight.getLatitudeE6() / 1E6
bottomRight.getLongitudeE6() / 1E6