[Casa-framework] 'pix' unit (was ia.moments)

[David King]

Just a tiny additional note on "pix" units, (which I am stumbling through at 
the moment):

As Wim indicates, "pix" isn't a valid unit string until you define it to be. 
  A one-shot (and static) routine WCBox::unitInit() is WCBox's way of 
accomplishing that, so that "pix" Units can be used subsequently in such 
regions (or anywhere else); it is called in all the WCBox constructors. 
(WCPoly has a similar routine.  I believe the WCRegion classes most actively 
support "pix" and essentially define its semantics).

Unfortunately, defining "pix" in the WCBox constructors is not quite soon 
enough, if you want to pass "pix" Quanta _to_ those constructors; 
furthermore, unitInit() is private.  As a workaround:

   WCBox dummy;

...will do the trick.  But I think making unitInit() public is slightly 
cleaner, and could do no conceivable harm.  Any opinion, Ger (or others)?

dk


>> Lindsey Davis wrote:
>> I am trying to use the moments task on an image whose shape is
>>
>> [256L, 256L, 1L, 31L]
>>
>> I tried both
>>
>> rtn = ia.moments([0],3)
>> rtn = ia.moments([0],4)
>>
>> because I am not sure how degenerate axes are handled but 
>> both give the following error
>>
>> ed Nov 29 22:46:54 2006    SEVERE image::moments:
>> Exception Reported: Unit::check Illegal unit string 'pix'


Wim.Brouw at csiro.au wrote:

> During the images production Neil wanted to be able to let the user
> specify things like 'pix' 'piel' 'beam' etc.
> The quanta can handle that (like it does in the case of FITS where
> things lik Km KM JY sec SEC etc are used) by having a user unit 'map'
> that can be filled at will. (pix e.g. is equanled to the countable non
> dimensional unit '_').
> In the original design this user map was a global static map; i.e. there
> should be persistence soemwhere).