.clock.shouldAnimate = true;
            var scene = viewer.scene;
            //开启对数深度缓冲区
            scene.logarithmicDepthBuffer = true;

            //火焰特效初始参数
            var viewModel = {
                emissionRate: 5.0, //排放率
                particleLife: 1.2, //粒子生命
                speed: 2.0, //速度
                startScale: 1.0, //起始规模
                endScale: 5.0, //终止规模
                particleSize: 25.0 //图像尺寸
      