params, api) {
                    var leftTop = api.coord([api.value(0), api.value(1)]);
                    var rightBottom = api.coord([api.value(2), api.value(3)]);

                    return {
                        type: 'image',
                        style: {
                            image: './data/hill-Qomolangma.png',
                            x: leftTop[0],
                            y: leftTop[1],
                            width: rightBottom[0] - leftTop[0],
                          