Cannot read property 'southwest' of undefined in Cesium

CesiumJS
1 
update(value:number) {
    this.altitude=value;
    this._viewer.camera.flyTo({
        destination : Cesium.Cartesian3.fromDegrees(this._viewer.Longitude,this._viewer.Latitude, value)
    });

I want to make it so that the function changes the height of the map, but there it must also take the coordinates of the point, and I need to change the height at any point where I am

2

Welcome to the Cesium Community!

Do you mind posting the full example of your code with the error reproduced? You can add the code to a Sandcastle.