WD-DALI-1.1 polygon winding direction

[Marco Molinaro]

Hi Pat, Arnold, all,

2016-09-08 18:56 GMT+02:00 Patrick Dowler <pdowler.cadc at gmail.com>:
> So, should I change the wording to say "when viewed from outside the
> unit sphere" and add STC reference? I want to say the minimum and
> leave the definitive specification in the hands of STC, but if we make
> readers go look it up in STC they will be annoyed.

I agree on referencing STC (even if it's not trivial because it would be nice
to have a pointer to 2.0 or general STC), but summarizing it in DALI.
I'm ok with the wording, is the group agrees (warning: if no one protest
means agreement).

Maybe, Arnold, can you suggest something
short and clear to put in DALI?
The reference text you replied is probably bullet-proof but too long for
the DALI spec (at least that's my opinion).

Cheers,
     Marco

>
> Pat
>
> On 8 September 2016 at 01:00, Felix Stoehr <fstoehr at eso.org> wrote:
>> Dear all,
>>
>> after some side-discussions with Marc I believe the following is true:
>>
>> - STC-S declares clockwise and counterclockwise with respect to the
>> celestial coordinate frame (north up, east to the left as seen from earth)
>>
>> - this is consistent with the footprintfineder.py output and thus all
>> the MAST/ALMA/ESA spectra
>>
>> - area calculations will be correct in this definition and coordinate frame
>>
>> - it is a bit counter-intuitive, because it means that anticklockwise
>> polygons in that definition are clockwise if you look up on the sky from
>> earth.
>>
>> It might be worthwile to declare in WD-DALI-1.1 the coordinate system in
>> which the clockwise/anticlockwise are defined, i.e. in which system to
>> "hold the clock".
>>
>> Best regards,
>>
>> Felix
>>
>
>
>
> --
> Patrick Dowler
> Canadian Astronomy Data Centre
> Victoria, BC, Canada