The worksheet window is the camera, R is the reference point for the projection, and V defines the horizon. For all to be well, we should have Camera --> R --> Horizon. If the Horizon line goes below the base of the cube, the points and lines change position smoothly across the transition, but the stated relationship between R, V and the cube cannot still be the same. There are some curious ways the relationships might be reconciled. [b]In Our Continuing Story of a Sleepy Mr. Land in Search of Perspective:[/b] Perspective Study 2: [url]http://www.geogebratube.org/material/show/id/33777[/url] ToDo: Define a reference height independent of objects in the scene.