How to compute the zoom level against returned markers?

Question

Hi,

I'd like to know if there is already a way to know from a given set of markers, the zoom I should apply to the map or do I have to do it my self? (this depends on the resolution so i expected to find it in MapView because it knows its boundaries...)

Regards, Zied Hamdi

Answer 1

Hi again,

I've attempted to do a method my self, it doesn't work perfectly but it seems sufficient (maybe I should round the quotient up to have the real value):

private void adjustZoomToMarkers(ArrayList<GeoLocationFlag> flags) {
 GeoPoint mapCenter = mapView.getMapCenter();
 int lat = mapCenter.getLatitudeE6(), lng = mapCenter.getLongitudeE6();
 int farestLat = 0, farestLng = 0;
 for (GeoLocationFlag geoLocationFlag : flags) {
  Log.d(LOG_TAG, "lat: " + geoLocationFlag.getLat());
  int flagLatDistance = Math.abs(geoLocationFlag.getLat() - lat);
  if (farestLat < flagLatDistance)
   farestLat = flagLatDistance;

  Log.d(LOG_TAG, "lng: " + geoLocationFlag.getLng());
  int flagLngDistance = Math.abs(geoLocationFlag.getLng() - lng);
  if (farestLng < flagLngDistance)
   farestLng = flagLngDistance;
 }
 Log.d(LOG_TAG, "farest: " + farestLat + "," + farestLng);
 Log.d(LOG_TAG, "spans: " + mapView.getLatitudeSpan() + "," + mapView.getLongitudeSpan());

 // compute how many times this screen we are far on lat
 float latQuotient = (float) farestLat / ((float) mapView.getLatitudeSpan() / 2);
 // compute how many times this screen we are far on lng
 float lngQuotient = (float) farestLng / ((float) mapView.getLongitudeSpan() / 2);

 int zoom = 0;
 if (latQuotient > 1 || lngQuotient > 1) {
  // must zoom out
  float qutient = Math.max((int) latQuotient, (int) lngQuotient);
  while ((qutient / 2) > 1) {
   qutient = qutient / 2;
   zoom--;
  }
 } else {
  float qutient = Math.max((int) (1 / (float) latQuotient), (int) (1 / (float) lngQuotient));
  while ((qutient / 2) > 1) {
   qutient = qutient / 2;
   zoom++;
  }

 }
 Log.d(LOG_TAG, "Zoom found " + zoom);

 int zoomLevel = mapView.getZoomLevel();
 mapController.setZoom(zoomLevel + zoom);
}

Best regards, Zied Hamdi

Answer 2

Hi,

As guessed when I was writing the answer above: when the quotient is eg. 9, it means you need more than 4 iterations to see it: so just correst both lines:

while ((qutient / 2) > 0.5) {

Best Regards, Zied Hamdi

Answer 3

int minLat = Integer.MAX_VALUE;
int minLong = Integer.MAX_VALUE;
int maxLat = Integer.MIN_VALUE;
int maxLong = Integer.MIN_VALUE;

for( GeoPoint l : points ) {
    minLat  = Math.min( l.getLatitudeE6(), minLat );
    minLong = Math.min( l.getLongitudeE6(), minLong);
    maxLat  = Math.max( l.getLatitudeE6(), maxLat );
    maxLong = Math.max( l.getLongitudeE6(), maxLong );
}

mapView.getController().zoomToSpan(Math.abs( minLat - maxLat ), Math.abs( minLong - maxLong ));

Answer 4

Hi Mike,

I like your code that is a lot shorter ;-), maybe I should only avoid creating new instances in the for loop to have the min and max points...

Best Regards, Zied Hamdi