Problem 330

I'm having a problem using G4PVPlacement to put G4Polycones inside of other
G4Polycones.

My initial observation is the definition of a local co-ordinate system seems to
be different for polycones as opposed to a simple solid such as a cube.  For a
cube, the center of the local co-ordinate system is the center of the cube.  For
a G4Polycone, the reference frame seems to be the same as the frame used to
define the (r,z) points of the polycone.

I don't regard the above as a problem.  Please don't change it.  Polycones can
be complicated enough without having to figure out where their centers are and
translating objects to be placed inside.

The problem is when placing a G4Polycone within the volume of another
G4Polycone.  The child G4Polycone is not placed such that its z=0 co-ordinate
(as defined by its vertices) is placed at the z=0 co-ordinate of the mother
G4Polycone; it's also not placed such that its z=0 co-ordinate is at the
geometric center of the mother polycone.  It appears to be placed roughly where
the geometric center of the child is aligned to the z=0 of the mother -- the
opposite of what one might expect from working with simple volumes.

I should mention that I'm working on a detector with cylindrical symmetry, with
the axis of rotation along the z-axis.  The mother and child G4Polycones both
have z=0 as their smallest z-coordinate, and I'm trying to place them such that
z=0 of both polycones corresponds to z=0 of the world volume.