[cube access] minutes from telecon (2013-07-03)

[Tim Jenness]

On Jul 22, 2013, at 21:34 , François Bonnarel <francois.bonnarel at astro.unistra.fr> wrote:

> Hello,
> Le 22/07/2013 19:03, Tim Jenness a écrit :
>> On Jul 22, 2013, at 00:52 , Markus Demleitner<msdemlei at ari.uni-heidelberg.de>  wrote:
>> 
>>> On Tue, Jul 16, 2013 at 12:15:32PM -0700, Patrick Dowler wrote:
>>>> - define a reasonable subset of STC-S that everyone can support, for
>>>> prototypes we will be strict and only support that subset; STC-S with
>>>> additional phrases will fail (note: the decision on ignoring vs
>>>> rejecting unexpected STC-S phrases will be reviewed later during WG
>>>> review)
>>>> 
>>>> - restrictions: only allow FK4, FK5, GALACTIC, ICRS
>>> Disclosure: I've never liked the notion of server-side coordinate
>>> transformations.
>>> 
>> and doesn't FK4 need an epoch?
> FK4 and FK5 need an Equinox

Yes but I was under the impression that accurate FK4 to FK5 also needed the epoch of the FK4 measurement.

>> 
>>> What's the use cases for letting the client specify reference systems
>>> in its cutout queries?
>>> 
>>> For cutouts, allowing this is particularly insiduous, since cutouts
>>> along the coordinate axes are no longer rectagular after a
>>> transformation, so services would have to resample, at least provided
>>> the result is supposed to come in the coordinate system requested
>>> (otherwise: What's the point at all?).  Of course, image formats
>>> usually only support rectangles -- should the unwanted voxels be
>>> NULL?  What else?
>>> 
>> I assume that the cutout service returns a rectangular area that just encloses the requested area.
> I agree with that
>>  Do we actually want to mask out the data if you specify a circular region? Or if you specify galactic and get back an ICRS image?
> No
>>> Conversely, server-side transformations need to touch all pixels,
>>> resample them, etc.
>>> 
>> I think I would tend to agree that you don't really want the image to be resampled by the server in order for the FK5 image to be returned as a galactic image. Client viewers will be able to display the galactic coordinate system on that FK5 image. The main reason for wanting the resampling is that you get a smaller image returned.
> Resampling and regridding facilities are among the use cases for AccessData functionalities for cubes. they actually need to force the output WCS and combine it with a cutout if necessary. So changing the coordinate system is part of what we CAN do with forcing the ouput WCS. But that's not in the scope of the current prototype.
> 

Great.

-- 
Tim Jenness