Oblique drawing principle — Are circles and angles that lie on planes perpendicular to the projection plane shown in true size and true shape in oblique projection?

Introduction / Context:
Oblique projection represents a 3D object with one principal face parallel to the projection plane while the depth is drawn along a receding axis. Understanding when shapes and angles are preserved as true is essential for technical sketching and CAD interpretation.

Given Data / Assumptions:

• Statement under test: features on planes perpendicular to the projection plane are true size/shape in oblique.
• In oblique drawings, the object face parallel to the projection plane is depicted without distortion.
• Receding planes are not parallel to the projection plane.

Concept / Approach:
True size/shape occurs when a feature lies in a plane parallel to the projection plane. Circles on that parallel face remain circles; angles on that face remain true. Features on planes perpendicular to the projection plane are foreshortened or distorted (e.g., circles appear as ellipses).

Step-by-Step Solution:
1) Identify the plane orientation: "perpendicular to the projection plane."2) Recall the rule: only planes parallel to the projection plane show true size/shape.3) Therefore, perpendicular planes will not show features in true size/shape.4) The statement is incorrect.

Verification / Alternative check:
Check a cylinder: its circular base parallel to the projection plane stays a circle; a base perpendicular to it becomes an ellipse. The angle preservation follows the same parallel-plane rule.

Why Other Options Are Wrong:

• Correct: False because perpendicular planes do not preserve true size/shape.
• Valid only for cavalier: No; the rule is geometric, not dependent on depth scale convention.
• Valid only for cabinet: Same reasoning; convention does not change plane parallelism.
• True for circles but not for angles: Both are not true on perpendicular planes.

Common Pitfalls:
Assuming depth-scaling choices (cavalier vs cabinet) affect truth of shape; confusing plane orientation with axis direction; overlooking that parallelism to the projection plane is the key determinant.

Final Answer:
Incorrect