Oblique sketching technique: When sketching an ellipse on a receding plane in an oblique drawing, is it acceptable to first block in the bounding rectangle and then sketch the ellipse tangent to the rectangle's sides to control proportions?

Introduction / Context:Ellipses appear when circles are viewed at an angle. In oblique drawings, circles on receding planes project as ellipses. A standard freehand technique is to inscribe the ellipse within a guiding rectangle, touching midpoints to manage width and height. This question checks knowledge of that practical method.

Given Data / Assumptions:

• Oblique projection keeps the front face true size; receding planes are foreshortened by convention (cavalier, cabinet, or general oblique).
• We are sketching, not constructing with exact loci.
• The target shape on the receding plane is an ellipse representing a circular feature.

Concept / Approach:The bounding-rectangle method creates guide points (midpoints on each side) where the ellipse must be tangent, ensuring consistent major/minor axes proportions under the chosen foreshortening. This improves accuracy and symmetry compared with drawing an ellipse freehand without guides.

Step-by-Step Solution:

Verification / Alternative check:Compare to ellipse templates or CAD-projected geometry; the inscribed ellipse closely matches the intended circle on the receding plane.

Why Other Options Are Wrong:The method is valid for cavalier, cabinet, and general oblique; it does not require a specific receding angle or isometric grids.

Common Pitfalls:Misplacing tangency points; unequal quadrant arcs; ignoring the foreshortening ratio leading to the wrong minor axis length.

Final Answer:Correct