ext.coords || (params.context.coords = []);
                    var key = lngIndex + '-' + latIndex;

                    // bmap returns point in integer, which makes cell width unstable.
                    // So we have to use right bottom point.
                    return coords[key] || (coords[key] = api.coord([
                        +(latExtent[0] + lngIndex * cellSizeCoord[0]).toFixed(6),
                        +(lngExtent[0] + latIndex * cellSizeCoord[1]).toFixed(6)
                    ]));
     