Cannot read property 'southwest' of undefined in Cesium

update(value:number) {
        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

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