[Esip-documentation] ACDD comments
Bob Simons - NOAA Federal via Esip-documentation
esip-documentation at lists.esipfed.org
Thu Sep 18 19:20:17 EDT 2014
Okay, below, I think you show a compound coordinate system (?) written
as WKT.
But my original question was: for the geospatial_bounds attribute (which
is a WKT representation of a geometry), what are the units of the
numbers and what is the coordinate system used in the geometry?
I see examples of WKT geometries (without units and without a coordinate
system) for example on Wikipedia, e.g.,
POLYGON ((30 10, 40 40, 20 40, 10 20, 30 10))
and I see examples of WKT coordinate systems (e.g., below).
But I still haven't seen a WKT geometry example which includes units and
a coordinate system. They always just have bare numbers. My point is:
how is a reader to know what the units and coordinate system are for the
geospatial_bounds WKT geometry?
Is geospatial_bounds always paired with some other ACDD attribute which
specifies its coordinate system?
If so, the ACDD documentation for geospatial_bounds should say so.
Or, must the WKT units be degrees_east, degrees_north, meters above the
geoid, using the WGS 84 coordinate system?
If so, the ACDD documentation for geospatial_bounds should say so.
Stated another way:
When a user sees e.g., POLYGON ((30 10, 40 40, 20 40, 10 20, 30 10))
(apart from having to read the spec to know which is the x value and
which is the y value),
how is the reader (human or computer) to know if those are degrees_north
and degrees_east values,
or if they are x and y from some projection?
Thanks.
On 2014-09-18 2:59 PM, David Neufeld - NOAA Affiliate wrote:
> Hi Bob,
>
> I don't think your questions appear dense, far from it. I also sense
> that your questions/comments are in part related to the difficulty of
> making changes to code based on evolving standards. This is a
> legitimate concern and can be part of the discussion IMO, correct me
> if this assumption is wrong.
>
> In terms of the actual standards which indeed are often verbose in the
> OGC space, below is a complex WKT example taken from GeoAPI which is
> a Java based reference implementation for many of OGC's standards (see
> http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html).
> I have a feeling that this may generate more questions around the
> complexity of supporting WKT for applications which use ACDD, but I
> think will at least reveal that WKT is a viable way to express
> geometries. Developing standards and consensus is hard I guess.
>
> Dave
>
> COMPD_CS <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#COMPD_CS>["OSGB36 / British National Grid + ODN",
> PROJCS <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#PROJCS>["OSGB 1936 / British National Grid",
> GEOGCS <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#GEOGCS>["OSGB 1936",
> DATUM <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#DATUM>["OSGB_1936",
> SPHEROID <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#SPHEROID>["Airy 1830",6377563.396,299.3249646,AUTHORITY <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#AUTHORITY>["EPSG","7001"]],
> TOWGS84 <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#TOWGS84>[375,-111,431,0,0,0,0],
> AUTHORITY <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#AUTHORITY>["EPSG","6277"]],
> PRIMEM <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#PRIMEM>["Greenwich",0,AUTHORITY <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#AUTHORITY>["EPSG","8901"]],
> UNIT <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#UNIT>["DMSH",0.0174532925199433,AUTHORITY <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#AUTHORITY>["EPSG","9108"]],
> AXIS <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#AXIS>["Lat",NORTH],
> AXIS <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#AXIS>["Long",EAST],
> AUTHORITY <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#AUTHORITY>["EPSG","4277"]],
> PROJECTION <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#PROJECTION>["Transverse_Mercator"],
> PARAMETER <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#PARAMETER>["latitude_of_origin",49],
> PARAMETER <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#PARAMETER>["central_meridian",-2],
> PARAMETER <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#PARAMETER>["scale_factor",0.999601272],
> PARAMETER <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#PARAMETER>["false_easting",400000],
> PARAMETER <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#PARAMETER>["false_northing",-100000],
> UNIT <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#UNIT>["metre",1,AUTHORITY <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#AUTHORITY>["EPSG","9001"]],
> AXIS <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#AXIS>["E",EAST],
> AXIS <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#AXIS>["N",NORTH],
> AUTHORITY <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#AUTHORITY>["EPSG","27700"]],
> VERT_CS <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#VERT_CS>["Newlyn",
> VERT_DATUM <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#VERT_DATUM>["Ordnance Datum Newlyn",2005,AUTHORITY <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#AUTHORITY>["EPSG","5101"]],
> UNIT <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#UNIT>["metre",1,AUTHORITY <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#AUTHORITY>["EPSG","9001"]],
> AXIS <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#AXIS>["Up",UP],
> AUTHORITY <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#AUTHORITY>["EPSG","5701"]],
> AUTHORITY <http://www.geoapi.org/3.0/javadoc/org/opengis/referencing/doc-files/WKT.html#AUTHORITY>["EPSG","7405"]]
>
> On Thu, Sep 18, 2014 at 3:40 PM, Bob Simons - NOAA Federal
> <bob.simons at noaa.gov <mailto:bob.simons at noaa.gov>> wrote:
>
> Hmmm. I'm sorry to be so dense. I see a 93-page document and the
> closest I can find to an answer about how to specify units for the
> numbers in a WKT geometry is the vague statement
> "NOTE In a coordinate reference system, the numbers shall be
> qualified by units."
> All the examples I see, e.g., pg XIX, lack units.
> (ACDD references Wikipedia
> http://en.wikipedia.org/wiki/Well-known_text,
> but I see no mention of units there, nor do any of the examples
> have units, nor do I see there how to specify a coordinate system
> within a WKT geometry.)
>
> And if I look at the BNF notation for a point in the OGC document
> <point> ::= <x> <y>
> I see
> <x> ::= <signed numeric literal>
> <y> ::= <signed numeric literal>
> but no units.
>
> I do see a separate section in the OGC document for specifying a
> coordinate system. Is ACDD's geospatial_bounds tied firmly to some
> other ACDD attribute which specifies the coordinate system? Or I
> am just unable to find the specification for specifying a
> coordinate system within a WKT geometry?
>
> Or, can you please just give me geospatial_bounds example (WKT
> which specifies units and a coordinate system) and add it to the
> ACDD specification)?
>
> Or if the units are assumed to be (must be) degrees_east,
> degrees_north, meters above the geoid, and uses the WGS 84
> coordinate system, then please say so in the ACDD specification.
> (Z datums for the ocean are notoriously hard. Most in-situ
> measurements are not relative to the geoid and many don't use WGS 84.)
>
> Thank you.
>
>
>
> On 2014-09-18 1:14 PM, David Neufeld - NOAA Affiliate wrote:
>> Hi All,
>>
>> Below is a link to the OGC Simple Features Specification which
>> includes how to represent features as Well Known Text. You will
>> find representations that include z values, units and coordinate
>> systems.
>>
>> http://portal.opengeospatial.org/files/?artifact_id=25355
>>
>> hth,
>> Dave
>>
>> On Thu, Sep 18, 2014 at 11:59 AM, John Graybeal via
>> Esip-documentation <esip-documentation at lists.esipfed.org
>> <mailto:esip-documentation at lists.esipfed.org>> wrote:
>>
>> As the person most involved in several of these, I guess I
>> will respond as best I can.
>>
>> On Sep 18, 2014, at 09:26, Bob Simons - NOAA Federal
>> <bob.simons at noaa.gov <mailto:bob.simons at noaa.gov>> wrote:
>>> * For geospatial_bounds, WKT doesn't specify units. So it is
>>> unclear if the WKT values represent latitude and longitude,
>>> or x and y from some projection (which opens up a huge can
>>> of worms). Please either require the use of latitude and
>>> longitude (please) or make some provision for specifying
>>> units (good luck with that).
>>
>> OK, I'm guessing we'll have to look into this. Thanks for
>> pointing it out. WKT is not specified well in Z either, if I
>> recall correctly.
>>
>
> --
> Sincerely,
>
> Bob Simons
> IT Specialist
> Environmental Research Division
> NOAA Southwest Fisheries Science Center
> 1352 Lighthouse Ave
> Pacific Grove, CA 93950-2079
> Phone: (831)333-9878 <tel:%28831%29333-9878> (Changed 2014-08-20)
> Fax: (831)648-8440 <tel:%28831%29648-8440>
> Email: bob.simons at noaa.gov <mailto: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.
> <>< <>< <>< <>< <>< <>< <>< <>< <>< <><
>
>
--
Sincerely,
Bob Simons
IT Specialist
Environmental Research Division
NOAA Southwest Fisheries Science Center
1352 Lighthouse Ave
Pacific Grove, CA 93950-2079
Phone: (831)333-9878 (Changed 2014-08-20)
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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