Creating a plane class as a waypoint before quadrilaterals

[whydoubt]

I've been playing around with the chapter on Quadrilaterals in book 2.
Seeing as it's good to have way-points through a chapter that let you see what progress has been made...
Here's the rough outline I'm going for:

• start with making a plane class (includes 'Finding the Plane', 'Ray-Plane Intersection').
• make a planes scene.
• extend the plane class to support planar shapes (includes 'Orienting Points on the Plane').
• create the quad class as a sub-class of the plane class (possibly within the same .h file).
• make the quads scene.