public static Spatial createSky(AssetManager assetManager, Texture west,
            Texture east, Texture north, Texture south, Texture up,
            Texture down, Vector3f normalScale) {
        return createSky(assetManager, west, east, north, south, up, down,
                normalScale, 10);
    }
Create a cube-mapped sky with radius=10 using six textures.

For the sky to be visible, its radius must fall between the near and far
planes of the camera's frustum.

@param assetManager from which to load materials
@param west texture for the western face of the cube
@param east texture for the eastern face of the cube
@param north texture for the northern face of the cube
@param south texture for the southern face of the cube
@param up texture for the top face of the cube
@param down texture for the bottom face of the cube
@param normalScale The normal scale is multiplied by the 3D normal to get
a texture coordinate. Use Vector3f.UNIT_XYZ to not apply and
transformation to the normal.
@return a new spatial representing the sky, ready to be attached to the
scene graph
jme3-core/src/main/java/com/jme3/util/SkyFactory.java