How do I determine the zoom level of a LatLngBounds before using map.fitBounds?

Question

I am trying to figure out a way of determining the zoom level of a Map before I call map.fitBounds(), and I cannot seem to find a way.

In the API v2 there was a method GMap.getBoundsZoomLevel(bounds:GLatLngBounds), but I can't find an equivalent in the API v3 documentation.

Is there a non-Google algorythm for determining what a zoom level will be beforehand?

Tool

There isn't an equivalent that is part of the standard library. What are you trying to achieve? You no longer have to pass a zoom level to setCenter. The v3 version of setCenter takes only 1 parameter, a google.maps.LatLng. – Verify

#6049475 – Ironworker

Answer 1

Nick is right, this discussion outlines a workable method: Google Maps V3 - How to calculate the zoom level for a given bounds

However, it is in Javascript. For those needing to do this with Android GMaps v3, the following is a translation:

private static final double LN2 = 0.6931471805599453;
private static final int WORLD_PX_HEIGHT = 256;
private static final int WORLD_PX_WIDTH = 256;
private static final int ZOOM_MAX = 21;

public int getBoundsZoomLevel(LatLngBounds bounds, int mapWidthPx, int mapHeightPx){

    LatLng ne = bounds.northeast;
    LatLng sw = bounds.southwest;

    double latFraction = (latRad(ne.latitude) - latRad(sw.latitude)) / Math.PI;

    double lngDiff = ne.longitude - sw.longitude;
    double lngFraction = ((lngDiff < 0) ? (lngDiff + 360) : lngDiff) / 360;

    double latZoom = zoom(mapHeightPx, WORLD_PX_HEIGHT, latFraction);
    double lngZoom = zoom(mapWidthPx, WORLD_PX_WIDTH, lngFraction);

    int result = Math.min((int)latZoom, (int)lngZoom);
    return Math.min(result, ZOOM_MAX);
}

private double latRad(double lat) {
    double sin = Math.sin(lat * Math.PI / 180);
    double radX2 = Math.log((1 + sin) / (1 - sin)) / 2;
    return Math.max(Math.min(radX2, Math.PI), -Math.PI) / 2;
}
private double zoom(int mapPx, int worldPx, double fraction) {
    return Math.floor(Math.log(mapPx / worldPx / fraction) / LN2);
}

Lyndel

Google API doc (developers.google.com/android/reference/com/google/android/gms/…) says "whole world is approximately 256dp wide" - Note: "dp", not "px". So, the excellent calculations above should be converted into "dp" (e.g. via the display metrics, "scaled density"). I used: double latZoom = zoom(mapHeightPx, WORLD_DP_HEIGHT * mDisplayMetrics.scaledDensity, latFraction); double lngZoom = zoom(mapWidthPx, WORLD_DP_WIDTH * mDisplayMetrics.scaledDensity, lngFraction); – Schaab

Besides the WORLD_PX_HEIGHT * density thing, I also needed to remove the Math.floor on zoom function, make it return float and set the int result as float result, otherwise I had bigger paddings then when using the bounds directly with deltas. Of course that all affected calls must change and don't forget that getBoundsZoomLevel also must return float. – Moyers