Hi Brian,
Yes, you're right, I overlooked that usage. And yes I agree that, to
"attach no specific meaning to the axis attribute [in the case of
generic spatial coordinates]" confuses the original intent.
Bob
On Nov 20, 2006, at 1:25 PM, Brian Eaton wrote:
> Hi Bob,
>
> I agree that your interpretation was our original intent when the axis
> attribute was included in CF. However I'm afraid we opened
> Pandora's Box
> by allowing axis to be used for "generic spatial coordinates", as
> described
> in the 3rd paragraph of section 4. In this relaxed interpretation
> it does
> make sense to use axis="X" on a coordinate with the standard_name
> projection_x_coordinate. In retrospect I'm starting to think that
> this was
> not one of our better ideas :-) By allowing axis to refer to generic
> coordinates you loose the ability to know that axis="X", when
> present, does
> in fact identify a longitude coordinate. In its current state the
> only
> information that can be derived from the axis attribute is that is
> provides
> a hint to the processor about how a coordinate might be plotted.
>
> It should probably be returned to it's original interpretation
> which you
> described. That was also the opinion voiced by Karl, and Jonathan
> too (I
> think, I've lost track of some of this thread).
>
> Brian
>
>
>
> On Mon, Nov 20, 2006 at 12:45:25PM -0800, Bob Drach wrote:
>> CDAT uses the axis attribute to identify the spatio-temporal type of
>> axis. (Since the axis attribute is optional, CDAT also checks the
>> units). My interpretation of the standard is that, if the axis is a
>> longitude, then axis="X" is appropriate, and this applies to
>> auxiliary longitude coordinate axes as well as 1-D lon(lon)
>> coordinate variables. However, it would not apply to
>> projection_x_coordinate, if I understand that attribute correctly.
>>
>> Bob
>>
>>
>> On Nov 19, 2006, at 6:05 PM, Simon Wood wrote:
>>
>>> Karl, Jonathan and others,
>>>
>>>> I'll reiterate what I said earlier (but I think somehow the email
>>>> didn't get distributed). I'm in favor of eliminating the
>>>> apparently contradictory statements. Of the two choices, perhaps
>>>> least confusion would result from adopting Jonathan's suggestion:
>>>> restrict X and Y to genuine longitude and latitude coordinates.
>>>
>>> By 'genuine longitude and latitude coordinates' would you intend to
>>> exclude auxiliary (lat/lon) coordinates (eg lat(y,x) and lon(y,x)),
>>> and allow only for datasets with lat lon dimensions (and hence lat
>>> (lat) and lon(lon) coordinate variables)?
>>>
>>> I'm a bit confused since I originally interpreted CF 4 to mean that
>>> the axis attribute as an extra way of identifying a coordinate
>>> variable. I assumed it would be good to use it with auxiliary
>>> coordinate variables for datasets using x,y dimensions and, say,
>>> lambert conformal projection. But then by analogy to the
>>> discussion about rotated pole projections on the earlier part of
>>> this thread I got to thinking that maybe the axis attribute should
>>> be associated with the x(x) and y(y) 'projection_x/y_coordinate'
>>> variables instead (ie so it can be used as a hint to the plot
>>> orientation).
>>>
>>> However, it seems to me that restricting the attribute to only be
>>> used for 'proper' coordinate variables (ie lat(lat), lon(lon)) is a
>>> bit drastic (and it doesn't really add much value to these
>>> variables does it?). All thats really needed is to resolve the
>>> ambiguity in intended usage (ie is it to hint at plot orientation
>>> or to help identify coordinate variables including auxiliary
>>> coordinate variables). Of course if both interpretations are in
>>> common use then it gets a bit trickier...
>>>
>>> The reason I was intending to use the axis attribute was just in an
>>> attempt to include as much metadata as possible so that (hopefully)
>>> a wider range of data readers would be able to understand our data;
>>> I guess if its just going to add confusion I won't use it. Does
>>> anybody know of data readers that currently rely on the axis
>>> attribute in any way?
>>>
>>> regards
>>>
>>> Simon
>>>
>>> --
>>> Simon Wood
>>> National Institute of Water and Atmospheric Research, Wellington,
>>> NZ
>>> simon.wood at niwa.co.nz
>>> http://www.niwa.co.nz
>>>
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Received on Mon Nov 20 2006 - 15:20:51 GMT
