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fact-project / fact-tools

The fact-tools are an extension to the streams framework to analyse the data of the First G-APD Cherenkov Telescope.
http://sfb876.tu-dortmund.de/FACT/
GNU General Public License v3.0
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Two definitions of Azimuth #75

Closed kbruegge closed 6 years ago

kbruegge commented 9 years ago

Originally reported by: mknoetig (Bitbucket: mknoetig, GitHub: mknoetig)

Hi guys,

I was working on a comparison of MAGIC and FACT data when I wanted to rotate the Theta[x] and Theta[y] coordinates back into the sky coordinates RA/DEC. I have written down a couple of things and will present those in a more comprehensive file. For now I wanted to point out two peculiarities of our system that I had to find first..

This first issue is about the code in SourcePosition.java .There, Fabian defines implicitly a second azimuth, parallel to the one stored in container "AzTracking". This ine os called "AzPointing".

From our discussions, following things about our azimuth got clear:

1.) AzTracking = -180deg -AzPointing

2.) AzTracking should not be used, as it is "uncorrected", in a sense.

Please find attached a plot displaying these issues. Maybe it would be useful, in order to get towards skymaps, to introduce a branch with proper coordinate transformations between all possible coordinate systems ( camera x/y, alt/az, ra/dec, ha/dec, ... ) that work on one consistent definition of the individual systems.

maxnoe commented 6 years ago

Also fixed by #231, we use astropys definition everywhere, Geographic North is 0°