Re: [Brahms-dev-l] question on coordinate systems

Dear Djamel

I am pretty sure there is NO such problem - the reason is there are test
program in
brat that has exploited all these dependencies when being developed.

I am though pretty sure the problem you see (and I see it too) is related to
that the real geometry
has small rotations in yz plane that is not taken into account in Brat. The
reason I know this is
am am modifiing brat to be able to use the geomtry directly (well at least
via another utility program to
generate the setup macro) and it has these issue. This is not quite
complete, but I am talking with Kris to solve
this final rotation problem (it is not trivial) while the bend plane was
rather simple just tedious
stay tuned.

Flemming



----------------------------------------------------------------
Flemming Videbaek
Physics Department
Brookhaven National Laboratory

e-mail: videbaek@bnl.gov
phone: 631-344-4106
----- Original Message ----- 
From: "Djamel Ouerdane" <ouerdane@nbi.dk>
To: "Brahms Devel List" <brahms-dev-l@lists.bnl.gov>
Sent: Thursday, July 22, 2004 9:11 AM
Subject: [Brahms-dev-l] question on coordinate systems


> Hello,
>
> I have a doubt about the way the detector volume class makes
> transformation from global to local. In x and z, I don't think there's any
> problem. But surprisingly, I think there is in y. Let me explain :
>
> I made a simulation using brag. I then converted the geant track to tpc
> tracks in T1, etc. Now, when I apply the standard global tracking modules,
> I get a momentum extremely close to the geant track momentum, and when I
> extrapolate the T1 track to the vertex plane, I get Vx = 0.  So in x,z
> that's fine.  But in y, it's different. I tuned the brag geometry so that
> it reflects the geometry in the DB for a given run. There are offsets in y
> for T1 and T2. Now, when I project back the TPC track of the simulation
> to the vertex plane, I get an offset which is equal to the TPC volume
> offset in y.
>
> My question to the experts : is the translation in y taken into account
> when going from local to global ? I haven't checked the relevant brat
> classes.
>
> Djam
>
>
> -- 
> Djamel Ouerdane ------------------------------------------o
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