Fx构造函数
# new G3DLayerType()
G3D-图层类型枚举
Example
let g3dLayer = viewer.scene.layers.getLayer(g3dLayerIndex);
let indexes = g3dLayer.getTerrainLayerIndexes();
indexes.forEach(i => {
let terrain = g3dLayer.getLayer(i);
let info = g3dLayer.getLayerInfo(i);
const { layerType } = info; // 此时的layerType是字符串类型，后续需要处理成数值型
let type = parseInt(layerType);
});