public Vector3f getCurrentCell() {
        return this.currentCamCell;
    }
Called when the camera has moved into a new cell. We need to
update what quads are in the scene now.

Step 1: touch cache
LRU cache is used, so elements that need to remain
should be touched.

Step 2: load new quads in background thread
if the camera has moved into a new cell, we load in new quads
@param camCell the cell the camera is in
jme3-terrain/src/main/java/com/jme3/terrain/geomipmap/TerrainGrid.java