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Rotations into the projection plane

Rotating flat

It is turning a plane around one of its traces (the hinge) until it lies on a projection plane. Whatever is in it appears in true size.

Rotating a point onto the horizontal plane

STEP 1 / 3

Plane, hinge and point

Plane α meets the horizontal plane along its trace α₁: that line is the hinge (it does not move). Point A lies in the plane, with its height above the PH.

What it is for: to measure distances and angles in true size, and to draw the real shape of a section. Everything rotated is written in brackets: (A), (r), (α).

What is rotated in each case

The rotation is always done on a hinge, which is a trace of the plane:

A point: perpendicular to the hinge, foot, and radius equal to the hypotenuse of the distance to the foot and the height.
A line: rotate two of its points and join them. If the line cuts the hinge, just rotate one point and join it to the crossing point, which does not move.
A plane: rotate a line of steepest slope; the angle it makes with the hinge is the angle of the plane with the PH.

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