GMouseWheelControl will automatically calculate the position of the map when the control is added and also when user's browser is resized. However, if the position of the map is changed dynamically, for example some contents were added/removed from the document on which the map was added to, you will need to use calculateMapPosition() method. Otherwise, scroll wheel option menu or the click & Pan icon will not appear at the correct location, when middle clicked on the map or used Shift + Click.