Changes of plane

Changing the plane

It is replacing one of the projection planes with another perpendicular to the one that stays. The object does not move: the point of view does.

True length of a segment

STEP 1 / 3

Segment and projections

AB is oblique: it does not appear in true length in either view. We need a plane from which it is seen face-on.

Golden rule: the coordinate of the plane that stays is kept; the one of the plane being replaced is changed for the new one. That is why lines are drawn perpendicular to the new ground line.

When a change of plane is needed

Practical rules:

To see a line in true length: a single change, with the new ground line parallel to one of its projections.
To see a plane edge-on: one change, with the new ground line perpendicular to its horizontal trace (or to the vertical one).
To see a plane in true size: two consecutive changes; the first one leaves it edge-on.
The coordinate that is kept is always the one of the plane that is not replaced.

Open the editor Solved exercises