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

[Patrick Dowler]

Below are my notes from short telecon we had to discuss some details of 
the cube access prototypes to be developed this summer.

Executive summary: a few simple params that define cutouts and flattening:

CUTOUT=<stc-S>
SUM=<axis>
AVG=<axis>

We will keep the STC-S simple to start (equatorial and galactic coords, 
no reference positions to complicate things, maybe support only 
wavelength and frequency for energy bounds, etc). This is *to start* and 
will be reviewed once we have a few prototypes and get to the WD stage.

At this point, I would encourage anyone interested in this to implement 
a simple parameter-based service, make it publicly accessible, and post 
something to this list with some examples that work. Then we can discuss 
what is ok, what is lacking, etc.

Pat

--
present: Pat (PD), Francois (FB), Doug (DT), Jose (JR), Felix (FS)


JR-prototype will include ~30 velocity (radio) cubes from Granada, 
working with CDS to integrate cutouts into Aladin

FB-mainly concerned with from the client point-of-view on using cutout 
services from Aladin

DT- VAO working on ImageDM, SIAv2 w/ access data, and cube access, but 
priorities will effect what is done; work planned or underway at 
multiple sites

PD-cubes from CGPS, a coupe from ALMA, also implementing cutout service 
on images (2d) and spectra (1d)


cutouts:

- agreed the scope was just to use STC-S to define the boundaries of an 
(STC term) AstroCoordArea, not other details about pixels, sample sizes, etc

- 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

- restrictions: not allowed to specify reference position; STC-S default 
of UNKNOWNREFPOS will mean service will not perform any transformations 
(this feasibly applies to all axes)

flattening:

- use different param(s) rather than try to bundle in the STC-S

- prototype: SUM=<axis> and/or AVG=<axis> where <axis> specifies which 
axis is to be flattened; multiple SUM params or AVG params could be 
specified to flatten on multiple axes (note: latter not discussed but I 
think it makes sense, esp. if someone wants to flatten two spatial axes 
to make a 1d spectrum from a cube)

- for the axis spec, we will need either to pull some labels from STC or 
another DM or make up some constants. TBD

- if CUTOUT and SUM (or AVG) are both specified, the semantics are that 
the cutout happens first, then the flattening

-- 

Patrick Dowler
Canadian Astronomy Data Centre
National Research Council Canada
5071 West Saanich Road
Victoria, BC V9A 2L9

250-363-0044 (office) 250-363-0045 (fax)
.