let measure = undefined
// 空间距离
function measureLineDistance()
{
    initmeasure()
    measure.drawLineMeasureGraphics({ clampToGround: 'clampToGround', callback: () => { } });
}
 // 空间面积
function measureArea()
{
    initmeasure()
    measure.drawAreaMeasureGraphics({ clampToGround: 'clampToGround', callback: () => { } });
}
// 三维量测
function measureHight()
{
    initmeasure()
    measure.drawTrianglesMeasureGraphics({ callback: () => { } });
}
// 清除
function measureClear()
{
    initmeasure()
    measure.measureClear();
}

function initmeasure()
{
    if(measure==undefined)
    {
        measure = new Cesium.Measure(viewer)
    }    
}