How to determine normal vector to create a plane

When I tried to create a plane like below,
name: “plane”,
position: new Cesium.Cartesian3(center[0],center[1],center[2]),
plane: {
plane: new Cesium.Plane(normal, 0.0),
dimensions: new Cesium.Cartesian2(20.0, 50.0),
material: Cesium.Color.BLUE.withAlpha(0.5),
I need to set a normal vector. Here, I am not sure about how to determine this vector because I am not familiar with the “Cartesian3” coordinates.

Read this


thank you, it works !