Le 30/09/2011 13:56, Jörg 'Yadgar' Bleimann a écrit :

> Attached is a view of another portion of the railing, showing how a
> standard 90° corner is supposed to look like...

The old mechanic in me is asking: how the hell do you assemble that ?
There is no visible crew on the holding vertical poles.
The horizontal rail seems to be made of one piece.
And the vertical poles seems to be fixed directly in the cement.

For your cylinder/sphere/torus seams... the intersection of a torus is a
circle (which connect to a sphere of same radius) only for 3 well-known
cutting planes. All other intersections of a torus with a plane is a 3D
curve which does not match a circle.

For a point P on a torus:
there is the plane parallel to the plane of symmetry of the torus.
there is the plane perpendicular to the previous plane and passing at
the centre of the torus.
and there is the plane for the Villarceaux circles. (also going via the
centre of the torus, with a slant)

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