Re: Problems with ARB geometry, will I use PLA !?

From: Alberto Fasso' <fasso_at_slac.stanford.edu>
Date: Wed, 23 Jun 2010 10:29:19 -0700 (PDT)

On Mon, 21 Jun 2010, Antonello Carloni wrote:

> Dear ALL,
> hallo again,
> I am experiencing trouble with the implementation of the objects drwan an=
> d
> coloured in blac in the picture attache.
> They are what in the old Fulka were called"ARBS".
> But when using the ARB card Fluka does not draw them,

If you have followed the discussion I had on this discussion list with Joe
Confort:
http://www.fluka.org/web_archive/earchive/new-fluka-discuss/2998.html
and following,
you will know that I have strongly recommended to never use ARBs.
On the other hand, Joe has attached some drawings where ARBs were drawn,
although there was a geometry error.

> So i decide to use Cards like PLA and XYP and YZP.

Good!

> No problems about the latter two ones but what about the definition of PL=
> A!?
> The manual just says:
>
> * 11. Generic infinite half-space. Code: PLA Each PLA is defined by 6
> numbers: H_x, H_y, H_z (x, y and z components of a vector of arbitrary
> length perpendicular to the plane), V_x, V_y, V_z (coordinates of any
> point lying on the plane). The half-space "inside the body" is that from
> which the vector is pointing (i.e., the vector points =F6utside"). A PLA
> definition extends over a single card in default fixed format, and over
> two cards in high-accuracy body fixed format.
.........
> And so what do those vectors Hx Hy Hz when describing the plane?!

Those are not "vectors", but the components of ONE vector (i.e. the projections
of a vector on the 3 coordinate axes.
One point and one vector define a generic plane without any ambiguity.
Notice that the magnitude, or length, of the vector is irrelevant. In general
I use a unit vector, so the H_x, H_y, H_z are just its direction cosines.
You can choose the direction of the vector as you like, but then you must
take it into account when you use the plane to "build" regions (you must
decide which part of space you prefer to be "inside" the plane, and which
"outside").

> For example , how to describe the 45=B0 XY Plane such as the A or B in the
> picture attached to this e mail!?
> Sorry to bother you all, i might be not so clever but the interpretation
> is really arb ,-)
> Thank you!

I am sorry, your attachment was unreadable on my mailing system. But the
manual is extremely clear. You need to input 6 numbers: 3 coordinates of
a point on the plane (any point, provided it is on the plane!) and 3 components
of a vector perpendicular to the plane (any vector, provided it is
perpendicular to the plane!) What is "arb" in all this?

Kind regards,

Alberto
Received on Wed Jun 23 2010 - 23:29:21 CEST

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