set Slippy Zoom Level
Set a new zoom level based on slippy tile level. When "follow position" is active the current position will be used as the reference point for the operation. In rest the screen center will be used. This may be between 0 and maxSlippyZoomLevel.
Return
The previous zoom level
Parameters
zoom Level
Slippy Zoom level
duration
The animation duration in milliseconds (0 means no animation)
xy
Screen coordinates under which map should keep position. The coordinates are relative to view parent screen.