[b]Exercise[/b][br]Change your position with right mouse button and view the construction from different sides.[br][list][br][*]Move the position of the [color=#1551b5]center of the projection[/color] in horizontal and vertical direction.[br][*]Show the horizontal plane and auxiliary lines by clicking on the check boxes.[br][*]Enlarge oder shorten the sphere by moving point B.[br][*]Choose[i] front elevation[/i] (upright projection) in the style bar.[br][*]The position of the image plane can moved with point P.[br][/list]