[fitsbits] Start of the FITS Region File Public Comment Period

[Malcolm J. Currie]

I'd rearrange the Definition to say earlier what a REGION table is and
offers, for anyone else who might wish to adopt this convention.  At
the moment the introduction tells how it's implemented before saying
what is it.

It doesn't state to which data the region is applicable.  Is the
convention limited to the primary data array or does it include any
IMAGE extensions?  If not, is there a way to association a region with
a specific array?  Can there be more than one REGION table in a FITS
file?

It assumes more prior knowledge of the reader than I would expect.  For
example, what's GTI?  It would help to have a reference or URL to GTI,
the IVOA STC Region syntax, OGIP/94-006, ACIS.  Please can "in the
usual way" in the first bullet of Section 2 be made explicit.

It wasn't clear which if any keywords are defined by the convention,
such as MFORM1.  In the example file I noticed an MFORM2 keyword.
Required keywords from other conventions like HDU* and MFORMn should
be referenced.

Aren't the long-string convention headers (even all the optional headers)
in Section 3 a distraction from the essence of the convention?

How should the unused values in the co-ordinate vectors be filled,
NaN, or doesn't it matter as you can work out how many to read
given the shape?

The sense and origin of ROTANG isn't always stated.  A factorisation
definition appearing Section 2 ROTANG rather than the imprecise
"rotation angle" would help.  It would be prudent to state the units,
although a FITS user might assume degrees.

Could the purpose and use of COMPONENT be elaborated.

The appears to be some duplicated text in Section 4.  "The value of
SHAPE...".

In the polygon definition can you use the same notation as in Table 1,
e.g. X subscript 0 rather than X[0].  Also indexing from 0 looks odd
for FITS.

Last sentence of Section 4.  Should "need to be" be "must be".

Could the example in Section 5 have some floating-point values too?

Minor gripes: Yuk to "soccer".  You mean association football or
perhaps you should use tennis.  (-:  Missing hyphens in Section 5:
"30-degree sector" and "40-degree sector", "left-hand side" and
"right-hand side".


Now a little off topic as we're only supposed to discuss the
description not the actual convention.  However, I did wonder why
MFORM1 was "X,Y" rather than a list of axis numbers.  That would make
it easier to extend to more dimensions.  Also have you considered other
operators like XOR or EQV?  I wondered if it were possible to
export a Starlink Ascii Region Definition (ARD) using this convention.
Most could export but not all, as ARD allows more than two dimensions
and has extra operators.

Hobbyhorse: I'd have used EXTTYPE = 'REGION', and EXTNAME for the
specific instances if you have more than one set of regions.

Malcolm Currie