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

[Tim Jenness]

On Jul 23, 2013, at 15:47 , Douglas Tody <dtody at nrao.edu> wrote:

> Interesting discussion.  My view, having read through all the postings,
> follows.
> 
> *** SUM, AVG, INTEG, moments, etc.
> 
> This is an important issue (especially for the more general AccessData
> problem, not just the cutout prototype).
> 
> 

…

> 
> For the simple "cutout" prototype this is too ambitious, it should be
> left to the AccessData prototyping, which we need for our full up cube
> access prototyping.  The most we might want to do is define more
> precisely what is permitted for something like SUM, e.g., if the
> channels are not equal in size, compute the integral instead.
> 

I'm not sure I understand. So if you have equal-sized channels you get the SUM but are lacking the information to be able to convert it to an integral. If you have unequal channels you do get the integral. Wouldn't it be easier to give you the integral every time? It seems that the difference between SUM and INTEG is so small that adding explicit support for INTEG is not much of an issue (but make sure the units on the output image are correct). The other moment maps are almost as easy if you use the naive formula.

More importantly, I find that naive SUM/INTEG are not as useful as you might think because you still can't see that weak line in the sum if there is a lot of baseline adding in lots of 0+/-noise to the SUM. The JCMT pipeline runs a clump-finding algorithm first and masks the baseline regions before calculating all the moment maps. This gives very nice results but I imagine is not something you want to be doing in a general service.

-- 
Tim Jenness