Jonathan,
We are attempting to follow section 9. The centroid of the weather system is calculated at each time step, and we are planning to use the longitude and latitude calculated as the coordinates of the system. So, for example, would the variables below be OK? (I?ve left out time and numerous other variables.)
float lat(trajectory, obs)
:standard_name = ?latitude?
:axis = ?Y?
:cell_methods = ?latitude:mean (over system)?
float lon(trajectory, obs)
:standard_name = ?longitude?
:axis = ?X?
:cell_methods = ?longitude:mean (over system)?
float maxlat(trajectory, obs)
:cell_methods = ?latitude:maximum (over system)"
float mtpwv(trajectory, obs)
:long_name = ?mean total precipitable water vapor?
:cell_methods = ?area:mean (over system)?
Grace and peace,
Jim
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On Mar 4, 2014, at 11:39 AM, Jonathan Gregory <j.m.gregory at reading.ac.uk> wrote:
> Dear Jim
>
> Is it a trajectory feature using the discrete sampling geometry convention
> of section 9? In that case it is required that there should be a nominal
> longitude, latitude and time for each observation along the trajectory.
> However you could also supply data variables of longitude and latitude with
> cell_methods along the same trajectory, and these data variables could be
> named by the coordinates attribute of other data variables (serving as
> auxiliary coordinate variables), to provide a more precise indication of
> location, as in section 9.5.
>
> Yes, the cell_methods would be "cell methods where there are no coordinates"
> of section 7.3.4 since you don't have longitude and latitude dimensions. It is
> permitted to specify "area:" for a cell method even if there are no horizontal
> dimensions specified.
>
> Cheers
>
> Jonathan
>
> ----- Forwarded message from Jim Biard <jbiard at cicsnc.org> -----
>
>> Jonathan,
>>
>> What I mean is, this is not gridded data. The operations being performed (mean latitude, etc) are over a geographic region that is not described anywhere in the file, which is the region considered to be the extent of the weather system. So, you are saying that this trajectory case falls under the ?Cell methods when there are no coordinates? case, is that right?
>>
>> Jim
>>
>> Visit us on
>> Facebook Jim Biard
>> Research Scholar
>> Cooperative Institute for Climate and Satellites NC
>> North Carolina State University
>> NOAA's National Climatic Data Center
>> 151 Patton Ave, Asheville, NC 28801
>> e: jbiard at cicsnc.org
>> o: +1 828 271 4900
>>
>>
>>
>>
>> On Mar 4, 2014, at 9:30 AM, Jonathan Gregory <j.m.gregory at reading.ac.uk> wrote:
>>
>>> Dear Jim
>>>
>>>> Even though there are no cells? That?s the part that I?m feeling confused about.
>>>
>>> Sorry, I'm not sure why you say there are no cells. "Cell" does not imply any
>>> number of spatial dimensions - is that the problem? It means the portion of
>>> the domain, of whatever dimensionality, which is represented by a particular
>>> data value. The cell_methods attribute indicates how that data value represents
>>> unrecorded variability of the quantity represented within the cell.
>>>
>>> Best wishes
>>>
>>> Jonathan
>>>
>>>> On Mar 3, 2014, at 1:22 PM, Jonathan Gregory <j.m.gregory at reading.ac.uk> wrote:
>>>>
>>>>> Dear Jim
>>>>>
>>>>> Yes, I think such an approach is applicable. Any data variable can have
>>>>> cell_methods and any data variable could be used as an aux coord variable.
>>>>> Although unusual, I don't see a reason not to have data variables of latitude
>>>>> and longitude, qualified by cell_methods, if required.
>>>>>
>>>>> Best wishes
>>>>>
>>>>> Jonathan
>>>>>
>>>>> ----- Forwarded message from Jim Biard <jbiard at cicsnc.org> -----
>>>>>
>>>>>> Subject: Re: [CF-metadata] can a cell method be an attribute of an auxiliary
>>>>>> coordinate variable ?
>>>>>> From: Jim Biard <jbiard at cicsnc.org>
>>>>>> Date: Fri, 28 Feb 2014 14:01:24 -0500
>>>>>> CC: cf-metadata at cgd.ucar.edu
>>>>>> To: Jonathan Gregory <j.m.gregory at reading.ac.uk>
>>>>>> X-Mailer: Apple Mail (2.1874)
>>>>>>
>>>>>> Jonathan,
>>>>>>
>>>>>> So, I?ve got a broader question. We have a case in hand with trajectory data for a physically extensive weather system. Two data variables are the mean longitude and latitude of the system, which we are treating as the auxiliary coordinate variables. Other data variables contain measurements such as maximum latitude at the mean longitude, etc. Are cell_methods applicable in this case? There is no grid, so the cell would be the area covered by the system, and the extents of this area are not described.
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>>
>
> ----- End forwarded message -----
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