David,
Yes. I think the wording could stand to be clearer. What I wonder is
what use is there for identifying a 2D grid of latitude values as being
an axis? I do a lot of satellite swath imagery and have worked with
polar stereographic data, and latitude is not an axis of my measurement
variable grid in either case.
I think part of the confusion arises from a somewhat unclear definition
of coordinate. I tend to use the phrase "true coordinate" for one that
is1-D, has a variable name equal to its dimension name, is monotonic,
has no fill values, etc, versus "auxiliary coordinate" for one that
doesn't meet one or more of those requirements. I generally assume that
true coordinates are being referred to when I see the word coordinate in
the Conventions unless it's made clear that is not the case (as in
Section 5 paragraph 6). With that reading, the coordinate type and
dimension type are one in the same in Section 4 paragraph 2, since only
true coordinate variables are being discussed.
Grace and peace,
Jim
On 3/31/17 12:28 PM, David Hassell wrote:
> Hi Jim,
>
> I agree you with in spirit, but the conventions do say that the axis
> attribute as being there to identify the *coordinate* type, rather
> than the *dimension* type (section 4, paragraph 2). Perhaps the
> wording here could be tightened up to say dimension type? I wonder how
> the axis attribute has been used over the last 6 years since 1.6 was
> released?
>
> All the best,
>
> David
>
> On 31 March 2017 at 17:04, Jim Biard <jbiard at cicsnc.org
> <mailto:jbiard at cicsnc.org>> wrote:
>
> David,
>
> As I read the Conventions, the axis attribute is to be applied to
> coordinate variables (Section 4. Coordinate Types and Section 5.
> Coordinate systems) to indicate that this variable can be treated
> as representing an dimensional axis of corresponding variable
> grids. Section 5 paragraph 6 talks about how it is still possible
> to figure out that an auxiliary coordinate variable is a
> spatiotemporal dimension of the if the axis attribute is not
> present. I don't think a 2D auxiliary coordinate variable can be
> considered to be a dimensional axis, can it?
>
> Grace and peace,
>
> Jim
>
>
> On 3/31/17 11:52 AM, David Hassell wrote:
>> Hello ?S?bastien and Jim,
>>
>> You are right to feel weird about identifying 2D lat and lon
>> as Y and X axes. The axis attribute should never be applied
>> to 2D variables. It is only valid for 1D "true" coordinate
>> variables.
>>
>> ?The axis attribute can be attached to auxiliary coordinate
>> variables with any number of dimensions. I would agree, though,
>> that attaching the axis=X attribute to a 2-d longitude auxiliary
>> coordinate variable is likely to confuse. The axis attribute's
>> purpose is merely to make identification easier, but as long
>> there are units of degrees_east (mandatory) and a standard name
>> of longitude (optional), humans and software alike should be happy.
>>
>> All the best,
>>
>> David
>>
>>
>> --
>> David Hassell
>> National Centre for Atmospheric Science
>> Department of Meteorology, University of Reading,
>> Earley Gate, PO Box 243, Reading RG6 6BB
>> Tel: +4
>> ?4 ?
>> 118 378 5613
>> http://www.met.reading.ac.uk/
>
> --
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> David Hassell
> National Centre for Atmospheric Science
> Department of Meteorology, University of Reading,
> Earley Gate, PO Box 243, Reading RG6 6BB
> Tel: +44 118 378 5613
> http://www.met.reading.ac.uk/
--
CICS-NC <http://www.cicsnc.org/> Visit us on
Facebook <http://www.facebook.com/cicsnc> *Jim Biard*
*Research Scholar*
Cooperative Institute for Climate and Satellites NC <http://cicsnc.org/>
North Carolina State University <http://ncsu.edu/>
NOAA National Centers for Environmental Information <http://ncdc.noaa.gov/>
/formerly NOAA?s National Climatic Data Center/
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