@Override
    protected void updateLOD(SafeArrayList<Vector3f> locations, LodCalculator lodCalculator) {
        TerrainGrid terrainGrid = (TerrainGrid)getSpatial();
        
        // for now, only the first camera is handled.
        // to accept more, there are two ways:
        // 1: every camera has an associated grid, then the location is not enough to identify which camera location has changed
        // 2: grids are associated with locations, and no incremental update is done, we load new grids for new locations, and unload those that are not needed anymore
        Vector3f cam = locations.isEmpty() ? Vector3f.ZERO.clone() : locations.get(0);
        Vector3f camCell = terrainGrid.getCamCell(cam); // get the grid index where the camera is (i.e. 2,1)
        if (terrainGrid.cellsLoaded > 1) {                  // Check if cells are updated before updating gridOffset.
            terrainGrid.gridOffset[0] = Math.round(camCell.x * (terrainGrid.size / 2));
            terrainGrid.gridOffset[1] = Math.round(camCell.z * (terrainGrid.size / 2));
            terrainGrid.cellsLoaded = 0;
        }
        if (camCell.x != terrainGrid.currentCamCell.x || camCell.z != terrainGrid.currentCamCell.z || !terrainGrid.runOnce) {
            // if the camera has moved into a new cell, load new terrain into the visible 4 center quads
            terrainGrid.updateChildren(camCell);
            for (TerrainGridListener l : terrainGrid.listeners) {
                l.gridMoved(camCell);
            }
        }
        terrainGrid.runOnce = true;
        super.updateLOD(locations, lodCalculator);
    }
Updates grid offsets and cell positions.
As well as updating LOD.

@author sploreg
jme3-terrain/src/main/java/com/jme3/terrain/geomipmap/TerrainGridLodControl.java