Lately, as I browse web for maps related questions on Android, what’s frequently requested is an example of setting bounds of a map (zooming to a proper level and panning) to be able show all of the pins given on the screen.
Most of the maps APIs provide this functionality such as Google Maps API, so developers seem to have problems with implementing theirs. Google Maps API for Android does not provide functionality for setting bounds to a box. Instead, what’s provided is to zoom to a span.
com.google.android.maps.MapController.zoomToSpan(int latSpanE6, int lonSpanE6)
latSpanE6 is the difference in latitudes * 10^6 and similarly lonSpanE6 is the difference longitude * 10^6. You may question how map controllers know where to zoom in just by the differences. For examples, kms between longitudes differ from equator to poles. Fortunately, Google maps projection has them in the same length. This may remind you the infamous South America versus Greenland syndrome. Although Greenland is much much smaller than South America, it doesnt look so with this map projection.
On the below, I implemented a boundary arranger method for MapView. Method takes three arguments: items, hpadding and vpadding. items as you may guess is a list of POIs. Other arguments are a little bit more interesting. hpadding and vpadding is the percentage of padding you would like to leave horizontally and vertically so that pins don’t appear just on the corners. For instance, if you assign 0.1 for hpadding, 10% padding will be given from top and bottom.
BTW, You’ll have to extend the existing MapView and add this method to your own MapView to use this method properly.
public void setMapBoundsToPois(List<GeoPoint> items, double hpadding, double vpadding) {
MapController mapController = this.getController();
// If there is only on one result
// directly animate to that location
if (items.size() == 1) { // animate to the location
mapController.animateTo(items.get(0));
} else {
// find the lat, lon span
int minLatitude = Integer.MAX_VALUE;
int maxLatitude = Integer.MIN_VALUE;
int minLongitude = Integer.MAX_VALUE;
int maxLongitude = Integer.MIN_VALUE;
// Find the boundaries of the item set
for (GeoPoint item : items) {
int lat = item.getLatitudeE6(); int lon = item.getLongitudeE6();
maxLatitude = Math.max(lat, maxLatitude);
minLatitude = Math.min(lat, minLatitude);
maxLongitude = Math.max(lon, maxLongitude);
minLongitude = Math.min(lon, minLongitude);
}
// leave some padding from corners
// such as 0.1 for hpadding and 0.2 for vpadding
maxLatitude = maxLatitude + (int)((maxLatitude-minLatitude)*hpadding);
minLatitude = minLatitude - (int)((maxLatitude-minLatitude)*hpadding);
maxLongitude = maxLongitude + (int)((maxLongitude-minLongitude)*vpadding);
minLongitude = minLongitude - (int)((maxLongitude-minLongitude)*vpadding);
// Calculate the lat, lon spans from the given pois and zoom
mapController.zoomToSpan(Math.abs(maxLatitude - minLatitude), Math
.abs(maxLongitude - minLongitude));
// Animate to the center of the cluster of points
mapController.animateTo(new GeoPoint(
(maxLatitude + minLatitude) / 2, (maxLongitude + minLongitude) / 2));
}
} // end of the method
