Spinning
It is turning an element around an axis until it sits in a convenient position. The element does not change: its position does.
Spin of a point around a vertical axis
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Axis and point
The axis is vertical and passes through O. In the plan it looks like a point; in the elevation, like a vertical line. A turns in a horizontal plane: its height does not change.
Spin of a line
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Spin two points
A line is defined by two points: spin both with the same axis and angle and join them.
The other axes
The vertical axis is the most common one, but others appear too:
- Pointing axis (perpendicular to the PV): the point keeps its distance. It turns in a plane parallel to the PV: in the elevation it describes a circle and in the plan it moves along a line parallel to the ground line.
- Axis parallel to the ground line: the point turns in a profile plane, perpendicular to the ground line. It must be solved in the third projection or with a change of plane.
- Oblique axis: avoided; it is replaced by a change of plane that makes it vertical or pointing.