Cesium obtains the latitude and longitude range of the screen

// viewer  Namely new Cesium.Viewer, Mount to window Yes , So you can use it directly 
function getCesiumViewerExtend() {
    
  let params = {
    };
  // computeViewRectangle, Calculate the approximate visible rectangle on the ellipsoid （ return  Rectangle）, If the oval is not visible at all , Then return to undefined.
  let extend = viewer.camera.computeViewRectangle();
  if (typeof extend === "undefined") {
    
    //2D You may not be able to pick up the coordinates under the ,extend return undefined, So do the following conversion 
    let canvas = viewer.scene.canvas;
    let upperLeft = new Cesium.Cartesian2(0, 0); //canvas Top left coordinate rotation 2d coordinate 
    let lowerRight = new Cesium.Cartesian2(canvas.clientWidth, canvas.clientHeight); //canvas The coordinates of the lower right corner turn 2d coordinate 

    let ellipsoid = viewer.scene.globe.ellipsoid;
    let upperLeft3 = viewer.camera.pickEllipsoid(upperLeft, ellipsoid); //2D turn 3D World coordinates 

    let lowerRight3 = viewer.camera.pickEllipsoid(lowerRight, ellipsoid); //2D turn 3D World coordinates 

    let upperLeftCartographic = viewer.scene.globe.ellipsoid.cartesianToCartographic(upperLeft3); //3D World coordinate to radian 
    let lowerRightCartographic = viewer.scene.globe.ellipsoid.cartesianToCartographic(lowerRight3); //3D World coordinate to radian 

    let minx = Cesium.Math.toDegrees(upperLeftCartographic.longitude); // Radian to latitude and longitude 
    let maxx = Cesium.Math.toDegrees(lowerRightCartographic.longitude); // Radian to latitude and longitude 

    let miny = Cesium.Math.toDegrees(lowerRightCartographic.latitude); // Radian to latitude and longitude 
    let maxy = Cesium.Math.toDegrees(upperLeftCartographic.latitude); // Radian to latitude and longitude 

    params.minx = minx; //  Minimum longitude 
    params.maxx = maxx; //  Maximum longitude 
    params.miny = miny; //  Minimum latitude 
    params.maxy = maxy; //  Maximum latitude 
  } else {
    
    //3D Access method 
    //  Maximum longitude 
    params.maxx = Cesium.Math.toDegrees(extend.east); // Radian to latitude and longitude 
    //  Maximum latitude 
    params.maxy = Cesium.Math.toDegrees(extend.north); // Radian to latitude and longitude 
    //  Minimum longitude 
    params.minx = Cesium.Math.toDegrees(extend.west); // Radian to latitude and longitude 
    //  Minimum latitude 
    params.miny = Cesium.Math.toDegrees(extend.south); // Radian to latitude and longitude 
  }
  return params; // Return to the latitude and longitude range of the screen 
}

Reprint ：https://blog.csdn.net/chenguizhenaza/article/details/116783045