Why do you think manholes are round in shape?
(You need to think a little crooked for this )
(In reply to re(3): A solution
A few points:
A triangle is more restrictive of entry for its size as the smaller widths (in relation to a side) make it harder for a worker to get through.
A triangle can get through the hole, though it might take almost deliberate action (say a vandal), bringing the point of the triangular cover near a corner of the hole and then sliding it so half the base of the cover is through and tilting it down so in effect an altitude of the cover is going through nearby and parallel to a side of the hole.
And of course, as the polygon gets more and more sides, it approaches being a circle, so rather than worry about odd angles, make it a circle for simplicity. In effect it's enough that a square is a bad choice because of the falling through.
Another advantage to a circle is that you don't have to get it oriented correctly to place it down on the hole.
Posted by Charlie
on 2003-02-19 18:31:09