using orbit Control
PC mouse:
- left: rotate
- middle (wheel ): zoom
- right: pan
Android touch:
- one finger move: rotate
- 2 finger span: zoom
- 2 finger move: pan
all works nice.
but on Android browser, when i scroll down the page
the canvas focus is lost 
and can not (touch) operate any more.
how to reactivate?
( besides page refresh )