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

[François Bonnarel]

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
>
>> 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.

Again Cutout functionality don't touch the pixels.

Regards
François
Use cases for resampling and regridding are different