Problem 252

Summary:	Inside-function with inward faces in G4Polycone
Product:	Geant4	Reporter:	h.boie
Component:	geometry/solids	Assignee:	davidw
Status:	RESOLVED WONTFIX
Severity:	normal	CC:	Gabriele.Cosmo
Priority:	P2
Version:	3.1
Hardware:	PC
OS:	Linux

Description h.boie 2001-04-26 08:40:36 CEST

The "Inside" function of G4Polycone does not consider if a side of the polycone
points outward or inward. So a point P in the Polycone will be detected to be
outside (because it's outside of an inward face).

I fixed this by introducing a boolean variable "inward" (witch should be set to
true for an inward face) in G4PolyconeSide and considered this in the Inside
function of the class. G4Polycone sets this flag for inward faces of the
polycone. (I hope you get these files as an attachment - if not and if your are
interessted in, please feel free to contact: me h.boie@mpi-hd.mpg.de)

Probably the same problem arises for similar solids but I didn't check this.

Thanks for developing Geant4, your doing a great job!

Yours hans

Comment 1 davidw 2001-04-30 13:16:59 CEST

I want to thank Hans Boie for looking into this problem, and for being
brave enough to investigate the code.

Hans has since discovered that the problem he is having is not associated
with G4Polycone or G4PolyconeSide, but may instead be associated with
G4ReplicaNavigation. I will encourage him to file another bug report
for G4Replica and will close this particular report.

To Hans and other readers, I would like to encourage them to do the following
when they believe they have found an error in a G4 solid:

     1. Please list the precise parameters used in creating the solid.

     2. List the precise point or trajectory which produces an error.

It would be particularly helpful if this information can be embedded in
a test program that we can run to reproduce the problem. Once we can
reproduce the problem ourselves, it should be simple to solve.

For reference, this is how G4Polycone decides which surfaces are inward
or outward facing:

Imagine slicing a polycone by a plane through the z axis. In this plane, the
polycone is represented by a series of connected R and Z points. G4Polycone
requires that these points are specified in a clockwise manner (see class
G4ReduciblePolygon). Each polycone side has a start point (r1,z1) and an end
point (r2,z2), and it is the order of these points that determines if a side is
inward or outward facing (for example, for an inward side, z1>z2). A vector
normal to the face is simply r = (z1-z2), z = (r2-r1).