Boxes and Polygons in ADQL/STC. Questions and recommendation.

[Alberto Micol]

On 24 Oct 2009, at 20:24, Tom McGlynn wrote:

> Roy Williams wrote:
>> It seems that the region specification does not support the RA/Dec  
>> limits, or the Glon/Glat limits, etc etc. All polygon boundaries in  
>> ADQL Region are great circles.
>> -- Is that correct?
>>
>> Therefore I assume the recommendation will say that such regions  
>> should NOT be implemented with ADQL Region, but should be  
>> implemented directly in the SQL query like this:
>>    RA between 200 and 210 and Dec between 20 and 30.
>> -- Is that correct?
>>
>>
>
> I think so.  There is one issue that might make it nice to have a  
> special function for this kind of box: the wrapping of longitude  
> values.  E.g.,  if I want the 20x20 box from 350 to 10 degrees in  
> lon and -10 to 10 in lat, the syntax is different than for the  
> region from 330-350 in lon.  So it would be nice to have some syntax  
> -- say rect -- which would allow users to specify
>
>   rect(350,10,-10,10) == rect(-10,10, -10,10) == rect(350,370,-10,10)
>

That "rect"  does not seem to be equally useful when spanning across  
the pole...
How do I express a rect that is centered at dec=85 and that extends 10  
deg in dec?

Al

> This allows users to specify the bounds consistently in whatever way  
> that is convenient to them.  It can also handle the housekeeping to  
> do this right (e.g., it would handle cases where the longitude is <0  
> or >360).  Otherwise there will be problems with tables that use  
> longitude values outside the canonical range.   We can say that's  
> user error, but I know that we (i.e., the HEASARC) have at least  
> some out of range values.
>
>   Tom