Projections of Points and Lines Questions and Answers

Answer: A

Rotating the horizontal plane downward then places the elevation above the reference line and the plan below it. Almost all engineering drawing is done in this quadrant, which is why the arrangement becomes second nature.

Answer: B

Correct answer: below the reference line

A point in the first quadrant lies above the horizontal plane and in front of the vertical plane. When the horizontal plane is rotated downward into the vertical, everything in front of the vertical plane swings below the reference line, so the plan falls below it and the elevation stays above. That separation is what makes the two views readable on one sheet.

Answer: C

Correct answer: above the reference line and its elevation below

The third quadrant is below the horizontal plane and behind the vertical plane. Rotating the planes together brings the point behind the vertical plane up above the reference line in plan, and the point below the horizontal plane down below it in elevation - the exact reverse of the first quadrant arrangement.

Answer: D

Zero height above the horizontal plane means the elevation cannot stand clear of the reference line at all. Its plan meanwhile lies at its true distance from the vertical plane, so the two views look quite unlike one another.

Answer: A

Correct answer: on the reference line

A point in the vertical plane is at zero distance in front of it, so its plan has nowhere to go when the planes are opened out and falls on the reference line itself. Its elevation shows its true height above the horizontal plane. The mirror case is a point in the horizontal plane, whose elevation lies on the reference line.

Answer: B

Only a point on the line of intersection can have zero height and zero distance from the vertical plane at once, so both its views coincide there. It is the single position at which plan and elevation are the same point.

Answer: C

Correct answer: in its true length

A line is projected without foreshortening onto any plane it is parallel to, so a line parallel to both principal planes appears at true length in both the plan and the elevation. It is the only attitude for which that is so, and it is why such a line can be measured directly from either view.

Answer: D

Correct answer: a point

A line perpendicular to a plane of projection is seen end on from that direction, so every part of it falls on the same spot and it projects as a point. Perpendicular to the vertical plane means a point in the elevation and a true length in the plan; the horizontal case gives the mirror image.

Answer: A

Correct answer: a point

Perpendicular to the horizontal plane means vertical, and a vertical line viewed from above is seen end on, so its plan is a single point at the position of both ends. Its elevation shows its true length, since the line is parallel to the vertical plane.

Answer: B

Correct answer: the elevation

A line parallel to the vertical plane is projected onto it without foreshortening, so the elevation shows both the true length and the true inclination to the horizontal. The plan is foreshortened by the cosine of that inclination. This is the attitude every true length construction aims to reach.