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

Thu Feb 26 14:05:19 EST 2015

I second this recommendation.  This is the way our GHRSST GDS2 granules are using ACDD attributes.

On Feb 25, 2015, at 1:02 PM, David Neufeld - NOAA Affiliate via Esip-documentation <esip-documentation at lists.esipfed.org<mailto:esip-documentation at lists.esipfed.org>> wrote:

Hi All,

I  recommend the examples for all resolutions be updated to drop embedded units, because the resolution will always refer to units of the axis.

In other words the units are already described by the following attributes: geospatial_lat_units, geospatial_lon_units, geospatial_vertical_units.

Duplicating units as an embedded value might minimally result in inconsistencies in the documentation.

The description could be revised along the lines of:
>From version 1.3 - Information about the targeted vertical spacing of points. Example: '25 meters'
To version 1.3.1 - Information about the targeted vertical spacing of points, units are referenced by the global attribute geospatial_vertical_units. Example: '25'

Dave

On Wed, Feb 25, 2015 at 11:51 AM, John Graybeal via Esip-documentation <esip-documentation at lists.esipfed.org<mailto:esip-documentation at lists.esipfed.org>> wrote:
Thanks for bringing this to our attention, Aaron.

Clearly this discrepancy was caused in our attempt to resolve existing ambiguity. (I for one assumed those mappings were semantic, not literal; and I didn't see any information that implied anything about the *format* of that field. There was also no guarantee that the units were specified, so that left the naked number essentially undefined.)  I'm truly sorry for the trouble it's causing.

Knowing now that there is a pre-existing practice means we have a dilemma. I'm not sure how heavily 1.3 has been implemented so far, but Bob implies at least one implementation, and you're seeing files with the problem.  it seems to me there are two options at this point, and I'm not sure either by itself is entirely sufficient:

1) Modify the translation software (and others?) to allow for the possibility of different units in version 1.3. (Presumably the hack way is to just parse the number assuming it is in the expected units, and issue an error if that seems to not be the case; the ideal way would be to modify the number into the desired units.)

2) Modify the specification for each resolution axis to require that resolutions be specified in the units of the corresponding axis, which must be defined. This would mean a bump to 1.4, and some modification for existing 1.3 users.

I propose we continue the discussion via email to see what the documentation cluster makes of this, and probably make it an agenda item at the next meeting. (Which is nominally tomorrow, though it isn't posted on the site at the moment. Maybe just a first reading of the issue tomorrow.)  Any chance you could join us at 11 AM?

John

On Feb 25, 2015, at 09:32, Aaron Sweeney via Esip-documentation <esip-documentation at lists.esipfed.org<mailto:esip-documentation at lists.esipfed.org>> wrote:

Hi, Bob et al.,

     I believe that these resolutions are currently mapped to ISO 19115-2 gco:Measures<https://geo-ide.noaa.gov/wiki/index.php?title=Measure>, 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><mailto: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.

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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<tel:303-497-4797>, Fax: 303-497-6513<tel:303-497-6513>

DISCLAIMER: The contents of this message are mine personally and do not necessarily reflect any position of NOAA.

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http://lists.deltaforce.net/mailman/listinfo/esip-documentation

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-ed

Ed Armstrong
JPL Physical Oceanography DAAC
818 519-7607

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