How is a USER FRAME plane defined?

• A. A single point and direction
• B. Two points: origin and XY
• C. Four points
• D. Three points, the origin, XX, and XY

Answer: (D)

A plane in a USER FRAME is defined by three non-collinear points, which fixes both position and orientation in 3D space. The origin sets where the frame sits, while the two other points, typically labeled XX and XY, establish the X and Y directions within that plane. With these three points, you can determine the plane’s orientation (its normal) and ensure the frame is uniquely defined. Using a single point with a direction would only describe a line, and two points define a line as well. Four points could lie in the same plane, but that’s redundant since three non-collinear points already define the plane. So the correct way to define the USER FRAME plane is with three points: the origin, XX, and XY.