public void setSafeMargin( ref btVector3 halfExtents, double defaultMarginMultiplier = 0.1f )
		{
			//see http://code.google.com/p/bullet/issues/detail?id=349
			//this margin check could could be added to other collision shapes too,
			//or add some assert/warning somewhere
			double minDimension = halfExtents[halfExtents.minAxis()];
			setSafeMargin( minDimension, defaultMarginMultiplier );
		}