Closed line along which a surface is generated by a moving line called a generatrix.
Example
Consider a generatrix that follows the contour of a simple closed line called the directrix.
This generatrix generates a surface.
Depending on the shape of the simple closed line, the generatrix, fixed at apex A :
- generates a conical surface, if the directrix is a closed curve;
- generates a pyramidal surface, if the directrix is a polygon.
Depending on the shape of the simple closed line, the generatrix, while always maintaining the same direction :
- generates a cylindrical surface, if the directrix is a closed curved;
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- generates a prismatic surface, if the directrix is a polygon.
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