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

John Graybeal jbgraybeal at mindspring.com
Thu Feb 26 00:09:23 EST 2015 

Aaron,

Many thanks for your thoughtful summary and reporting of issues. It definitely helps us get a grip on the specification and how to use it.  Please do offer any other insights you come across.

> Should I not even attempt to use geospatial_[lat|lon|vertical]_resolution in my netCDF files?

The attributes in question do not appear to apply to your case (unless you have multiple points at different lat, lon, or height locations, but it sounds like you don't). So all this may be our problem, but you can ignore it now.

> while the attribute crosswalk to ISO 19115-2, as documented at http://wiki.esipfed.org/index.php/Attribute_Convention_for_Data_Discovery_(ACDD)_Mappings,

My apologies -- I tried to update these pages to indicate they were no longer normative (although they give strong hints, at least!). I have updated this page now.

John

---------------
John Graybeal, Project Lead
Marine Metadata Interoperability Project: http://marinemetadata.org
MMI Ontology Registry and Repository: http://mmisw.org/orr


On Feb 25, 2015, at 18:51, Aaron Sweeney - NOAA Affiliate via Esip-documentation <esip-documentation at lists.esipfed.org> wrote:

> Thanks for the background on the naming, John.  To be clear, Bob, I did not ask for an attribute to be renamed.
> 
> Perhaps it's worth pointing out that I, as a new netCDF user and creator, am attempting to the best of my ability to read and understand all relevant documentation, and when questions arise, I am reaching out to a community of experts through this mailing list.
> 
> Perhaps some discussion of my efforts thus far will help toward mutual understanding.  The netCDF files I am creating are of point feature type (station timeseries data) and comply with the CF conventions for discrete sampling geometries and for standard names.  This work was greatly assisted by the existence of template CDL files (and decision tree!) put together by the NODC netCDF Team (thanks, Ajay, and others).  
> 
> I am also endeavoring to comply with the most recent ACDD documentation (v1.3).  I found an inconsistency in the ACDD-1.3 documentation regarding geospatial_[lat|lon|vertical]_resolution.  (To sum up, the example in the Description is a text string with a numerical value and uom, while the attribute crosswalk to ISO 19115-2, as documented at http://wiki.esipfed.org/index.php/Attribute_Convention_for_Data_Discovery_(ACDD)_Mappings, maps this attribute to a gco:Measure, which can only contain a numeric value.)  This inconsistency came to light when I attempted to generate ISO 19115-2 metadata from my netCDF via TDS (and in particular ncISO) and discovered that the ISO did not validate.  I traced the problem back to ACDD, hence my appeal to all of you for clarity.
> 
> In doing so, it came to my attention that the intent of the geospatial_[lat|lon|vertical]_resolution was to describe an aspect of gridded data (thanks again, John).  Here, I must express some apprehension, since I am not working with a grid feature type, but rather a point feature type.  I do not know what the solution is.  Should I not even attempt to use geospatial_[lat|lon|vertical]_resolution in my netCDF files?
> 
> Cordially,
> Aaron
> 
> On Wed, Feb 25, 2015 at 6:18 PM, Bob Simons - NOAA Federal <bob.simons at noaa.gov> wrote:
> For ACDD 1.4, I welcome suggestions for new attributes.
> 
> For ACDD 1.4, I welcome suggestions for changes to the definitions of existing attributes that clarify or improve the wording or add useful examples, but I discourage changes that change the meaning or usage of attributes. It is a standard. We generally accept it as is. 
> 
> I do not welcome suggestions for changing the names of current attributes.  Everybody has that kind of suggestion, but our suggestions often disagree. The current names are used by software and datasets. It's best not to even think about changing them unless there is some absolutely compelling case/need.
> 
> I do not welcome suggestions for ACDD version 1.3.1.  We haven't done "second decimal" versions before. I think it is a bad idea to ratify new versions of standards frequently. We should debate this and vote on this before we start accepting suggestions for ACDD 1.3.1.  
> 
> If there is a significant disagreement (as arose here) between how some software is using an attribute and how the attribute is defined in a ratified version of ACDD, I think the software should be changed, not ACDD.  (And I'm one of those software guys.) It is hard to imagine situations where that isn't true. That's what standards are for. That's what standards are all about. 
> 
> 
> 
> 
> 
> 
> On Wed, Feb 25, 2015 at 4:43 PM, David Neufeld - NOAA Affiliate <david.neufeld at noaa.gov> wrote:
> Bob I think you've made a good summary about how standards development and discussions often occur in our community, however I also like to think that new ideas and contributions are welcomed and even encouraged!  A discussion list seems like the right place to put those ideas forward even though they may not ultimately be accepted.  
> 
> Dave
> 
> On Wed, Feb 25, 2015 at 2:07 PM, Bob Simons - NOAA Federal via Esip-documentation <esip-documentation at lists.esipfed.org> wrote:
> Aaron, please understand that ACDD, like CF, is a standard. Successive versions of the standard are hammered out by seemingly endless discussions and numerous votes (with the hope of reaching consensus) by people in the community. Once a version of a standard is ratified (as ACDD 1.3 is), you should treat it as if that version were written in stone. Software (like ncISO, THREDDS, ERDDAP) is written to work according to the standard, not the other way around (unless it is something new that is being added to the standard). And if you don't like an attribute's name, (to be blunt) tough. It is what it is. You could have lobbied for some other name before the attribute first made it into ACDD. But now that it is in ACDD, please don't advocate changing it just because you think a slightly different name is more appropriate. Lots of software and thousands of datasets have been written to follow the ACDD standard. They shouldn't have to change just because you think a slightly different name is more appropriate. That's why we try hard to get standards right the first time. That's why we try very hard not to make changes to successive versions of ACDD (and other standards) that conflict with previous versions.
> 
>  
> 
> On Wed, Feb 25, 2015 at 12:29 PM, Aaron Sweeney via Esip-documentation <esip-documentation at lists.esipfed.org> wrote:
> Hi, John,
> 
>      Why are these attributes not called "geospatial_[lat|lon|vertical]_spacing", rather than "geospatial_[lat|lon|vertical]_resolution", if, in fact, the intention, as indicated in their Descriptions, is to capture the "targeted spacing of points"?
> 
>      My first inclination, upon reading the name of the attribute "geospatial_[lat|lon|vertical]_resolution", was to interpret it to mean "how well the numerical value of [lat|lon|vertical] is resolved."
> 
> Cordially,
> Aaron
> 
> 
> 
> 
> On 02/25/2015 01:19 PM, John Graybeal via Esip-documentation wrote:
>> 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 
>>> 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 
>>> 
>>> 
>>> 
>>> _______________________________________________
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>> 
>> 
>> 
>> _______________________________________________
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> 
> -- 
> 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
> 
> 
> 
> 
> -- 
> Sincerely,
> 
> Bob Simons
> IT Specialist
> Environmental Research Division
> NOAA Southwest Fisheries Science Center 
> 99 Pacific St., Suite 255A      (New!)
> Monterey, CA 93940               (New!) 
> Phone: (831)333-9878            (New!)
> Fax:   (831)648-8440
> Email: bob.simons at noaa.gov
> 
> The contents of this message are mine personally and 
> do not necessarily reflect any position of the 
> Government or the National Oceanic and Atmospheric Administration.
> <>< <>< <>< <>< <>< <>< <>< <>< <>< 
> 
> 
> _______________________________________________
> Esip-documentation mailing list
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> http://lists.deltaforce.net/mailman/listinfo/esip-documentation
> 
> 
> 
> 
> 
> -- 
> Sincerely,
> 
> Bob Simons
> IT Specialist
> Environmental Research Division
> NOAA Southwest Fisheries Science Center 
> 99 Pacific St., Suite 255A      (New!)
> Monterey, CA 93940               (New!) 
> Phone: (831)333-9878            (New!)
> Fax:   (831)648-8440
> Email: bob.simons at noaa.gov
> 
> The contents of this message are mine personally and 
> do not necessarily reflect any position of the 
> Government or the National Oceanic and Atmospheric Administration.
> <>< <>< <>< <>< <>< <>< <>< <>< <>< 
> 
> 
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