Multi-dimensional Data Access minimal requirements

[Douglas Tody]

Note that all proposals being discussed provide support for this
feature, e.g., POS,SIZE with a single SIZE value defines a circular
region centered at a given position (in the coordinate space of a
specific spatial frame it also defines a nonrotated box).  Certainly
this is the most common and most useful spatial cutout and defines the
absolute minimum required.  The point being made is that allowing SIZE
to have two values, specified as angular extents, is still a simple
cutout but provides sufficient flexibility to fully describe a
nonrotated spatial image cutout, e.g. of a large cube or wide field
survey.   - Doug


On Wed, 12 Mar 2014, Bruce Berriman wrote:

> I have to agree with you - we have had an image cutouts service at IPAC for a number of years. Users were clear they wanted circular cutouts, so that was implemented. Any pixel that is enclosed partially or wholly within the boundary of the circle is returned.
>
> Bruce
>
>
> On Mar 11, 2014, at 1:59 PM, Tom McGlynn <Thomas.A.McGlynn at nasa.gov> wrote:
>
>> Douglas Tody wrote:
>>> On Tue, 11 Mar 2014, Robert J. Hanisch wrote:
>>>
>>>> On 3/11/14 3:49 PM, "Douglas Tody" <dtody at nrao.edu> wrote:
>> ...
>>>> But either way,
>>>> I still think "circle" is not what one wants for a cutout.  It's ok for
>>>> discovery, but not for a cutout.
>>>
>>> Exactly.  Circle is usable for discovery but not very useful to specify
>>> the ROI for a cutout.  Note that in the discovery use case, there are
>>> also issues with the size and coverage of the target image - is the
>>> center of the target image in the specified circular region, or only
>>> part of the image, is it fully contained, etc. (this was the point of
>>> the INTERSECT parameter).
>>>
>>
>> I don't think I agree.  What's wrong with the following?
>>
>> Hypothetical use case:  I've got 1000 distant galaxies in the Hubble deep field and I want to extract ACS data on each of them.  I'm planning on doing some kind of photometry that needs to go out 5" from the center.  So I request 1000 cutouts as circles with a radius of 5" and the appropriate centers.  I get back 1000 cutouts that are presumably rectangles (probably squares but maybe a pixel or two off).
>>
>> Seems pretty reasonable to me.  It would be much harder if I have to first calculate the bounding box in RA/Dec for the circle that I need, and it may also be less efficient, since the ACS images may not be nicely aligned with the coordinate system in which I specify my box. So I'd get back larger boxes than I actually needed -- a factor or two more area in the worst case I think.
>>
>> Recognize that the SIA service is going to have to calculate bounding boxes for a misaligned box even if we are going to only allow boxes. The circle case will almost always be easier for the SIA service to calculate.
>>
>>
>>
>> 	Tom
>
>