Google Maps Calculate Zoom

calculateZoom.kt

    /**
     * Calculates the zoom level for the StreetWatchMap using the formula given by a Google employee (maps team)
     * in https://groups.google.com/d/msg/google-maps-js-api-v3/hDRO4oHVSeM/osOYQYXg2oUJ. For simplification
     * the formula has been duplicated and simplified below
     *
     * R = RequestedMeterRadius
     * S = MinScreenSizeInDp
     * B = BaseMetersPerPixel (for the type of map)
     * L = Latitude (Center of focus)
     * Z = ZoomLevel
     *
     * (2R)/S = (B * Cos(L * PI / 180)) / (2^Z)
     *
     * which solving for Z becomes
     * Z = log2((B * Cos(L * PI / 180) * S) / (2R))
     *
     * @param viewSize The size of the [MapView] in DP
     * @param geoLocation The location at the center of the view
     * @param requestedRadius The radius around the [geoLocation] in Meters
     */
    fun calculateZoom(viewSize: Point, geoLocation: GeoLocation, requestedRadius: Int): Float {
        val latitudeRadian = geoLocation.latitude * Math.PI / 180
        val top = BASE_METER_PER_DP * Math.cos(latitudeRadian) * Math.min(viewSize.x, viewSize.y)

        val total = top / (requestedRadius * 2).toFloat()
        return total.log(2.0).toFloat()
    }

    val zoomLevel = calculateZoom(Point(mapView.width.pxToDp(), mapView.height.pxToDp()), geoLocation, radius)

                val cameraUpdate = CameraUpdateFactory.newCameraPosition(
                        CameraPosition.Builder().apply {
                            target(LatLng(geoLocation.latitude, geoLocation.longitude))
                            zoom(zoomLevel)
                        }.build()
                )
    map.moveCamera(cameraUpdate);