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Forum: Particles
Re: Question Angle distribution from direction cosines (valentina)
Date: 04 Feb, 2008
From: Marc Verderi <Marc Verderi>

Hi Valentina,

I am a bit surprised by the "-" signs, but assuming this is due to some 
convention (I'm unfamiliar with gps) you can calculate the angles as:

q = acos(-Pz)
f = atan2(-Py, -Px)

The atan2 function takes care of the sign of "-Py" to put the f angle in 
the right part of the trigonometric circle.

Cheers,
Marc

PS: if the "-" signs are not there, just remove them everywhere in the q 
and f expressions.

valentina a écrit :
> *** Discussion title: Particles
> Email replies to PublicHyperNews@slac.stanford.edu must include:
>   In-Reply-To: <"/particles/383"@geant4-hn.slac.stanford.edu>
>   Subject: ...change this to be about your reply.
>
> Hi, my Geant4 output file gives me the direction cosines (DX, DY, DZ) of
> the particle. I have to calculate theta and phi (spherical coordinates)
> from these cosines and I'm using:
>
> theta = acos(-MZ) phi = atan(DY/DX)
>
> >From the GPS Users Manual I have found:
>
> The direction cosines are calculated as
>
>         Px = - sin(q) cos(f)
>         Py = - sin(q) sin(f)
>         Pz = - cos(q)
>
> The problem is that the result is bit strange and I don't know if I'm
> using a wrong transformation. Can someone help me?
>
> Thanks! Valentina
>   


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1 None: Re: Angle distribution from direction cosines   (michel maire - 04 Feb, 2008)
(_ None: Re: Angle distribution from direction cosines   (Vladimir IVANTCHENKO - 05 Feb, 2008)
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