[Esip-documentation] ACDD comments

Thu Sep 18 19:15:01 EDT 2014

Thanks all for a lively thread -- my net is down and my phone is small. So I will see what y'all think when I can actually see it in less time. More later. - John

On Sep 18, 2014, at 2:59 PM, David Neufeld - NOAA Affiliate via Esip-documentation <esip-documentation at lists.esipfed.org> 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["OSGB36 / British National Grid + ODN",
>     PROJCS["OSGB 1936 / British National Grid",
>         GEOGCS["OSGB 1936",
>             DATUM["OSGB_1936",
>                 SPHEROID["Airy 1830",6377563.396,299.3249646,AUTHORITY["EPSG","7001"]],
>                 TOWGS84[375,-111,431,0,0,0,0],
>                 AUTHORITY["EPSG","6277"]],
>             PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],
>             UNIT["DMSH",0.0174532925199433,AUTHORITY["EPSG","9108"]],
>             AXIS["Lat",NORTH],
>             AXIS["Long",EAST],
>             AUTHORITY["EPSG","4277"]],
>         PROJECTION["Transverse_Mercator"],
>         PARAMETER["latitude_of_origin",49],
>         PARAMETER["central_meridian",-2],
>         PARAMETER["scale_factor",0.999601272],
>         PARAMETER["false_easting",400000],
>         PARAMETER["false_northing",-100000],
>         UNIT["metre",1,AUTHORITY["EPSG","9001"]],
>         AXIS["E",EAST],
>         AXIS["N",NORTH],
>         AUTHORITY["EPSG","27700"]],
>     VERT_CS["Newlyn",
>         VERT_DATUM["Ordnance Datum Newlyn",2005,AUTHORITY["EPSG","5101"]],
>         UNIT["metre",1,AUTHORITY["EPSG","9001"]],
>         AXIS["Up",UP],
>         AUTHORITY["EPSG","5701"]],
>     AUTHORITY["EPSG","7405"]]
> 
> On Thu, Sep 18, 2014 at 3:40 PM, Bob Simons - NOAA Federal <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> 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> 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 (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. 
>> <>< <>< <>< <>< <>< <>< <>< <>< <>< <><
>> 
> 
> _______________________________________________
> Esip-documentation mailing list
> Esip-documentation at lists.esipfed.org
> http://www.lists.esipfed.org/mailman/listinfo/esip-documentation
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.lists.esipfed.org/pipermail/esip-documentation/attachments/20140918/8282bc05/attachment.html>