cesium添加扩散圆环

let r1 = 50;
let r2 = 50;
 
viewer.entities.add({
    id: quality.id,
    position: Cesium.Cartesian3.fromDegrees(position),
    billboard: {
        image: 'imgUrl',
        width: 40,
        height: 40,
        horizontalOrigin: Cesium.HorizontalOrigin.CENTER,
        verticalOrigin: Cesium.HorizontalOrigin.Bottom,
    },
    ellipse: {
        semiMinorAxis: new Cesium.CallbackProperty(function () {
            r1 = r1 + 0.5;
            if (r1 >= 100) {
                r1 = 0;
            }
            return r1;
        }, false),
        semiMajorAxis: new Cesium.CallbackProperty(function () {
            r2 = r2 + 0.5;
            if (r2 >= 100) {
                r2 = 0;
            }
            return r2;
        }, false),
        height: _center[2] + 1,
        material: new Cesium.ImageMaterialProperty({
            image: imageUrl,
            repeat: new Cesium.Cartesian2(1.0, 1.0),
            transparent: true,
            color: Cesium.Color.WHITE.withAlpha(1),
        })
    }
})