[QUANTITY] Data Model for Quantity v0.5

[David Berry]

Brian,

> The whole point of moving getCurrent[Coords|Value]Quantity to the locator
> is that you  may have more than one locator open for a Q at a time. If you place it on
> the parent Q, then you are restricted to traversal only in one frame at a time
> which is a needless restriction. After all, there should be no "favored frames",
> it is the job of the locator (I think) to pick which frame it wants to use for
> traversal (and to instruct the parentQ which values to return).

This was another issue on which we retired gasping to our corners. The
concept of traversal "in a Frame" means nothing to me, and consequently I
can see no need for locators. For instance, you have an image of the south
celestial pole in which "lines" of constant dec are actually circles -
in this situation what does it mean to "traverse the image in (RA,Dec)"?
What order are the pixels returned in? As far as I can see it only makes
sense to return them in the natural order they are stored in the image
(1,1), (1,2), (1,3), ... (2,1), (2,2), (2,3), ...

How can you define any other order? And if you always get the pixel back
in the same order then what is the point of locators?

You may say "I have already answered that" - if so, sorry, but I didn't
follow your answer.


David

----------------------------------------------------------------------
Dr David S. Berry    (dsb at ast.man.ac.uk)

STARLINK project		 |	Centre for Astrophysics
(http://www.starlink.ac.uk/)	 |	University of Central Lancashire
Rutherford Appleton Laboratory	 |	PRESTON
DIDCOT				 |	United Kingdom
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