Curved surfaces
Cylinder, cone and sphere have no edges: they are drawn by their apparent outline and, if needed, by auxiliary generators or parallels.
Cylinder and cone
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Cylinder: base and outline
In the plan it is a circle; in the elevation, a rectangle whose height is that of the cylinder. The extreme generators are the outline.
Cone and sphere
The other two solids of revolution:
- Right cone: in the plan it is a circle and in the elevation an isosceles triangle. The apex projects onto the centre of the base; the extreme generators are the outline.
- Sphere: it projects as two circles of the same radius, with their centres on the same vertical. The apparent outline is the equator in the plan and the meridian parallel to the PV in the elevation.
- In all three solids the apparent outline is a continuous line; the inner generators are thin lines.