[Esip-documentation] ACDD-1.3 documentation change request: Descriptions of "resolution" attributes

John Graybeal jbgraybeal at mindspring.com
Wed Feb 25 15:19:13 EST 2015 

I am trying to find a good ncISO rep to be a part of this discussion -- with luck David Neufeld will jump in soon, or people can suggest another rep, perhaps from Unidata? 

Not sure yet if we're having a call tomorrow, for now I am assuming we are.

I'm not sure that many current users are using this value the way it is documented: "Information about the targeted spacing of points". That does not mean either the accuracy or precision of the value, but the (intended) distance between points in a grid of values -- but often these values appear in data sets for single fixed stations, which seems invalid. 

And as Jim B points out (thank you), the original ISO mapping assumes the grid sizes are georectified -- but some/many grids in earth science are laid out in non-angular constant steps (meters). I assumed we want to support those cases, and no one found fault with the examples -- but maybe they are flawed, if georectified is a constraint. Alternatively, units of meters (or plain, non-geo degree) could be mapped to non-georectified ISO grid resolution terms.

John 

On Feb 25, 2015, at 10:59, Jim Biard via Esip-documentation <esip-documentation at lists.esipfed.org> wrote:

> Hi.
> 
> I checked this as well, and there should clearly be both a floating-point number and a units for a resolution entry. As Aaron showed in his email, the units go in a 'uom' attribute on the gco:Measure element, and the number is the value of the element. If ncISO isn't doing this, then that sure appears to be an ncISO bug.
> 
> There is another issue, of a sort, that this points up. The geospatial_(lat/lon)_resolution attributes in the documentation Aaron listed allow for units that are nonsensical (to me, anyway), such as meters for a quantity that should be restricted to angular units. You can get away with it for latitude, but there is no way to create a longitude axis on a grid that has constant steps in non-angular units.
> 
> Grace and peace,
> 
> Jim
> 
> On 2/25/15 12:32 PM, Aaron Sweeney via Esip-documentation wrote:
>> Hi, Bob et al.,
>> 
>>      I believe that these resolutions are currently mapped to ISO 19115-2 gco:Measures, as in:
>> 
>> geospatial_lat_resolution -->
>> <gco:Measure uom="[geospatial_lat_unit]">[geospatial_lat_resolution]</gco:Measure>
>> 
>> geospatial_lon_resolution -->
>> <gco:Measure uom="[geospatial_lon_unit]">[geospatial_lon_resolution]</gco:Measure>
>> 
>> geospatial_vertical_resolution -->
>> <gco:Measure uom="[geospatial_vertical_unit">[geospatial_vertical_resolution]</gco:Measure>
>> 
>> The GEO-IDE wiki page on gco:Measure (link above) indicates that the value should be an "XML Schema double."
>> 
>>      Also, the earlier ACDD-1.1 documentation includes the ISO 19115-2 path as:
>> /gmi:MI_Metadata/gmd:spatialRepresentationInfo/gmd:MD_Georectified/gmd:axisDimensionProperties/gmd:MD_Dimension/gmd:resolution/gco:Measure
>> 
>> Cordially,
>> Aaron
>> 
>> On 02/25/2015 10:17 AM, Bob Simons - NOAA Federal wrote:
>>> Is that an error in ACDD or in ncISO? (I don't know. I think it is
>>> debatable.) It is probably easier to change ncISO than to change ACDD
>>> (at least until the next version which is probably far off) and all
>>> datasets which follow the recommendations of the ACDD documentation.
>>> 
>>> On Wed, Feb 25, 2015 at 9:11 AM, Aaron Sweeney via Esip-documentation
>>> <esip-documentation at lists.esipfed.org> wrote:
>>>> Hi, folks,
>>>> 
>>>>       I want to bring to your attention a problem with the ACDD-1.3
>>>> documentation that is leading to the creation of invalid ISO 19115-2
>>>> metadata records.
>>>> 
>>>>       Specifically, I am referring to the Descriptions of the following
>>>> Suggested global attributes: geospatial_lat_resolution,
>>>> geospatial_lon_resolution, and geospatial_vertical_resolution.  For
>>>> reference and clarity, I've included these attributes (as well as their
>>>> related units attributes) and their descriptions from the ACDD-1.3
>>>> documentation below this message.
>>>> 
>>>>       There are two problems with the Description of these "resolutions."
>>>> The first is the recommendation to include both a numerical value and unit.
>>>> The ncISO tool expects these resolutions to be numeric only.  This leads to
>>>> the creation of invalid ISO 19115-2 records.  The second problem is that the
>>>> Description does not require the unit of resolution to be the same as the
>>>> corresponding "geospatial_[lat|lon|vertical]_unit."
>>>> 
>>>>       I would advocate that the Description of resolution explicitly state
>>>> that a numeric value is expected and that the value be expressed in the same
>>>> unit as specified in the corresponding "geospatial_[lat|lon|vertical]_unit"
>>>> attribute.
>>>> 
>>>> Cordially,
>>>> Aaron
>>>> 
>>>> ----relevant ACDD-1.3 documentation follows----
>>>> 
>>>> geospatial_lat_units: Units for the latitude axis described in
>>>> "geospatial_lat_min" and "geospatial_lat_max" attributes. These are presumed
>>>> to be "degree_north"; other options from udunits may be specified instead.
>>>> geospatial_lat_resolution: Information about the targeted spacing of points
>>>> in latitude. Recommend describing resolution as a number value followed by
>>>> the units. Examples: '100 meters', '0.1 degree'
>>>> geospatial_lon_units: Units for the longitude axis described in
>>>> "geospatial_lon_min" and "geospatial_lon_max" attributes. These are presumed
>>>> to be "degree_east"; other options from udunits may be specified instead.
>>>> geospatial_lon_resolution: Information about the targeted spacing of points
>>>> in longitude. Recommend describing resolution as a number value followed by
>>>> units. Examples: '100 meters', '0.1 degree'
>>>> geospatial_vertical_units: Units for the vertical axis described in
>>>> "geospatial_vertical_min" and "geospatial_vertical_max" attributes. The
>>>> default is EPSG:4979 (height above the ellipsoid, in meters); other vertical
>>>> coordinate reference systems may be specified. Note that the common
>>>> oceanographic practice of using pressure for a vertical coordinate, while
>>>> not strictly a depth, can be specified using the unit bar. Examples:
>>>> 'EPSG:5829' (instantaneous height above sea level), 'EPSG:5831'
>>>> (instantaneous depth below sea level).
>>>> geospatial_vertical_resolution: Information about the targeted vertical
>>>> spacing of points. Example: '25 meters'
>>>> 
>>>> 
>>>> 
>>>> --
>>>> Aaron D. Sweeney
>>>> Water Level Data Manager
>>>> 
>>>> Cooperative Institute for Research in Environmental Sciences (CIRES)
>>>> University of Colorado at Boulder
>>>> and
>>>> NOAA National Geophysical Data Center
>>>> Marine Geology and Geophysics Division
>>>> 325 Broadway, E/GC3
>>>> Boulder, CO 80305-3328
>>>> 
>>>> Phone: 303-497-4797, Fax: 303-497-6513
>>>> 
>>>> DISCLAIMER: The contents of this message are mine personally and do not
>>>> necessarily reflect any position of NOAA.
>>>> 
>>>> 
>>>> _______________________________________________
>>>> Esip-documentation mailing list
>>>> Esip-documentation at lists.esipfed.org
>>>> http://lists.deltaforce.net/mailman/listinfo/esip-documentation
>>>> 
>>> 
>> 
>> -- 
>> Aaron D. Sweeney
>> Water Level Data Manager
>> 
>> Cooperative Institute for Research in Environmental Sciences (CIRES)
>> University of Colorado at Boulder
>> and
>> NOAA National Geophysical Data Center
>> Marine Geology and Geophysics Division
>> 325 Broadway, E/GC3
>> Boulder, CO 80305-3328
>> 
>> Phone: 303-497-4797, Fax: 303-497-6513
>> 
>> DISCLAIMER: The contents of this message are mine personally and do not necessarily reflect any position of NOAA.
>> 
>> 
>> _______________________________________________
>> Esip-documentation mailing list
>> Esip-documentation at lists.esipfed.org
>> http://lists.deltaforce.net/mailman/listinfo/esip-documentation
> 
> -- 
> <igjdgbcb.png>                                                          Visit us on 
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