Projection of circles on oblique planes: If a circle lies in a plane that is not parallel to the plane of projection, will its image appear as an ellipse rather than as a true circle?

Introduction / Context:Orthographic and pictorial projection rules explain how shapes transform when viewed from different angles. Circles are a classic case: their appearance depends on the angle between the circle’s plane and the projection plane.

Given Data / Assumptions:

• A circle is on a plane tilted relative to the projection plane.
• Standard parallel projection (orthographic or axonometric) is considered.
• No special auxiliary view is used to make the circle appear in true shape.

Concept / Approach:When a plane is inclined to the projection plane, figures on it are foreshortened. A circle becomes an ellipse under parallel projection because all points are projected along parallel lines, compressing one dimension. Only when the circle’s plane is parallel to the projection plane does it remain a true circle in that view.

Step-by-Step Solution:

Verification / Alternative check:Build a simple model: a ring held at an angle appears elliptical to the eye or in a camera image; aligning it perpendicular restores the circular appearance.

Why Other Options Are Wrong:

Common Pitfalls:Forgetting to switch to an auxiliary view to dimension the true diameter; drawing a circle symbol on an inclined face without proper ellipse construction.

Final Answer:Correct