Measure a rectangle at normalised $(u,v)$ coordinates.

Input parameters:

1. Rc → Rectangle to measure.
2. Ut → Normalised $u$ parameter, along the width.
3. Vt → Normalised $v$ parameter, along the height.

Output parameters:

1. Pl → Plane at $(u,v)$ parameters.
2. Pt → Rectangle corner closest to $(u,v)$ parameters.
3. Ln → Edge closest to $(u,v)$ parameters.