Isometric Projection Questions and Answers

Answer: B

A box whose edges are isometric lines is drawn first and the object's features are located by offsets measured along those edges. It converts every non-isometric line into a pair of measurable isometric coordinates, which is why the method is so general.

Answer: C

One diameter of the circle lies along an isometric line and foreshortens with it while the perpendicular diameter foreshortens differently, which is exactly the condition for an ellipse. It is why isometric drawings of holes and shafts are set out as ellipses throughout.

Answer: D

The rhombus that encloses the circle has unequal diagonals, and the ellipse touches the midpoints of its sides with its major axis along the longer one. Getting the two diagonals the wrong way round produces an ellipse visibly tilted against the face it should lie in.

Answer: A

Two arcs of large radius and two of small are struck from the corners and the diagonal intersections of the enclosing rhombus. Being circular arcs it is not a true ellipse and departs slightly near the ends of the axes, which is accepted for the speed it offers.

Answer: B

Only lengths along isometric lines survive the projection in a predictable ratio; an angle between two such lines opens or closes according to the plane it lies in. A 90 degree corner of the object appears as either 60 or 120 degrees on the drawing.

Answer: C

Which of the two it becomes depends on the orientation of the corner within its isometric plane. It is the clearest demonstration that angular measurement on an isometric drawing is meaningless without reference to the underlying object.

Answer: D

A grid of isometric lines is laid over the orthographic view and each point of the curve is located by its two offsets, then plotted in the isometric box. Enough points are taken for a smooth curve to be drawn through them by hand or with a template.

Answer: A

Its silhouette is the same circle from every direction, so no foreshortening applies to the outline itself. In a true isometric projection that circle has the sphere's actual diameter, which is the one case where projection and drawing coincide in size.

Answer: B

Keeping the front face parallel to the plane of projection leaves it in true shape, with the depth drawn at an angle. It is a great convenience where that face carries most of the detail, particularly circles which stay circular rather than becoming ellipses.

Answer: C

Halving the depth counteracts the exaggerated appearance that cavalier projection gives, since drawing the depth full size makes the object look unnaturally long. Both forms keep the front face true, which is the defining property of oblique projection.