Michael Kohl wrote:
>Please apologize that I add my opinion here (don't want to cause
>confusion).
>
>To my view there is still a difference between the polar coordinate
>systems where theta measures the polar angle with respect to the z axis
>and phi measures the azimuthal angle with respect to the x axis, thus
>theta ranges [0,180] and phi [0,360]. Shifting phi to [-90,270] is simply
>a rotation of the polar coordinate system around the z-axis.
>
>Tong's coordinate system with negative theta's and phi's within
>[-90,90] might be symmetric and convenient for visualization
>but is not a polar coordinate system in the above sense.
>
>The physics finally should usually given in a conventional polar
>coordinate system.
>
>
> Michael
>
>
>
>
>
>>Douglas Hasell wrote:
>>
>>>Hi,
>>>
>>> Unfortunately I have thought of a plausible reason for using
>>>the range [-90,270) for the azimuthal angle which Chris suggested today.
>>>
>>> Something that we might do rather naively for a given track is
>>>determine its azimuthal angle by taking the average of the azimuthal
>>>angles for the track segments which make up the track. So if the track
>>>segments have azimuthal angles 1, 359, 0 for example, then the average
>>>(180) clearly isn't what we want.
>>>
>>> Hopefully people are clever enough to avoid this sort of error
>>>but I can imagine it slipping through on occasion.
>>>
>>> Not saying I'm convinced we should start changing code yet but
>>>maybe....
>>>
>>> Cheers,
>>> Douglas
>>>
>>>26-415 M.I.T. Tel: +1 617 258 7199
>>>77 Massachusetts Avenue Fax: +1 617 258 5440
>>>Cambridge, MA 02139, USA E-mail: hasell@mit.edu
>>>
>>Hi,
>>
>>This is exactly why my symetric system is superior to
>>others even though it is unconventional (or I reversed the
>>definition of theta and phi).
>>My theta runs from -Pi to +Pi and phi runs from -Pi/2 to +Pi/2.
>>Therefore, negative (positive) theta is left (right) sector, and
>>negative (positvie) phi is bottom (top) half of the chamber.
>>Just looking at the two angles, you can visualize where the
>>track is going^;^.
>>
>>-T
>>
>>
>>
>>
>
Yes, it is not polar coordinate system.
But it is trivial to translate to polar system and we are doing it already.
And I agree that for the BLAST coordinate system, we should use
more conventional system.
-T
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