[OSGeo-Standards] Re: FW: [MetaCRS] 'FOSS Maintained' Source of CRS Definitions

Thu May 8 03:29:15 EDT 2008

On Wed, May 7, 2008 18:30, Landon Blake wrote:
> Frank wrote: "Can you point us to a public document on this model?"
>
>
> This might be an issue with the ISO spec. You have to pay for copies of
> ISO specs if I remember correctly. They are also protected by copyright,
> which might be another issue for some of us.

Another side note: One thing that OGC is adamant about is to publish
standards openly and royalty free. All ISO standards that have gone
through ISO TC211 and were developed with involvement by OGC members are
therefore also available for free. Cool thing I'd say.

Apart from that it is obviously easier to just hack into an existing
library that already implements standards like GeoTools and GeoAPI does.
Whenever you do need to look into the original papers and cannot find them
let the standards list now. Several OGC members are involved with FOSSGIS
and OGC has offered several slots to OSGeo to be used by independent
developers to access documents still under development. If you need more
information please let me know, I am happy to act as enabler.

Regards,

>> From the ISO FAQ:
>>
>
> Are any ISO standards available electronically?
>
>
> Some ISO standards are available as electronic products. Contact the ISO
> member in your country or our sales department using the online contact
> form.
>
>
> Where can I obtain technical assistance on standards?
>
>
> Contact the ISO member in your country. A list of members can be
> accessed on this site. The ISO Central Secretariat does not provide
> technical assistance, but the online enquiry service may be able to help
> you save time by directing you to appropriate sources of information.
>
> Can I reproduce material from ISO standards?
>
>
> All ISO publications, including ISO standards, are protected by
> copyright. See the ISO copyright guide page for further information.
>
> The web page for the newest version of the ISO 19111 spec being
> developed is here:
>
> http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.
> htm?csnumber=44075
>
> Frank wrote: " I'd be interested to hear from the CS-MAP folks if they
> model datum shifts between arbitrary datums, as opposed to mapping
> everything through WGS84 (as PROJ4 is inclined to do)."
>
>
> We talked about this at OpenJUMP a few months back. It seems design of a
> CRS library is simpler if you use WGS84 as the common currency for
> transformations, but it adds overhead for some more simple transformations.
> For example, you don't need to convert to WGS84 to go
> from California State Plane Coordinates in US Survey Feet to California
> State Plane Coordinates in Metric units. You just scale. We had thought
> a solution would be to break transformations into two (2) types. Simple
> transformations that could be performed with scaling, rotation, and an
> elevation shift, and everything else, which would use WGS84 as a medium.
>
> Frank wrote: " A few limitations to WKT that I am concerned about..."
>
>
> Could we extend the format? I don't really think it is critical that we
> use WKT. As long as we have something that is human readable text, and not
> locked up in a relational database.
>
> The only advantage of an extended WKT format is that it is already known
> to a lot of programmers.
>
> Frank wrote: " When talking about dictionaries I would prefer not to get
> hung up on API specifications.  I'd prefer to manage and provide a
> dictionary in some form suitable exploitation by different packages and
> leave it to them to talk about APIs."
>
> I agree. I'm speaking to Jody about setting up a mailing list that can
> host discussions on collaboration between Java projects.
>
> Landon
>
>
>
> -----Original Message-----
> From: metacrs-bounces at lists.osgeo.org
> [mailto:metacrs-bounces at lists.osgeo.org] On Behalf Of Frank Warmerdam
> Sent: Wednesday, May 07, 2008 8:24 AM
> To: Martin Desruisseaux
> Cc: metacrs at lists.osgeo.org
> Subject: Re: [MetaCRS] "FOSS Maintained" Source of CRS Definitions
>
>
> Martin Desruisseaux wrote:
>
>> There is already an existing model, which is an international standard
>>
>
>> approved both by ISO and OGC: ISO 19111. Would it be an acceptable
> model?
>
> Martin,
>
>
> Can you point us to a public document on this model?  I'm frankly
> somewhat intimidated by it, and concerned that a lot of stuff it describes
> is not practically useful.  But I really need to do a current review
> before I spout off much more.
>
>>>> There is already a "standard" and open format for CRS definitions,
>>>> namely WKT, correct? Couldn't this be used?
>>
>> It can be used for "minimal" CRS definition. But the OGC standard WKT
>> can not express Bursa-Wolf parameters targeting any other datum than
>> WGS84, and can not contain useful metadata like area of validity. Yet
>>
> it
>> still applicable when there is nothing better. But when a choice is
>> possible, I rather push for the EPSG database.
>
> I'd be interested to hear from the CS-MAP folks if they model datum
> shifts between arbitrary datums, as opposed to mapping everything through
> WGS84 (as PROJ4 is inclined to do).
>
>
> A few limitations to WKT that I am concerned about:
> * There is no way to express datum shift methods other than 3/7
> parameter transformations to wgs84 (via TOWGS84).  In particular, how am I
> supposed to document use of grid shift files in WKT? * There is no way to
> express that there are more than one possible datum shift approximation
> available for use. * No way to mark coordinate systems as deprecated,
> categorize them for display to the user and such.  If we produce a "super
> dictionary" it would be nice if user interfaces could provide a useful
> navigation mechanism to user based on it.
>
> I can imagine picking the ISO model as our central CRS data model, and
> distributing definitions in some format that maps well to that model, like
> GML, but I'm concerned we make our dictionaries so complicated that they
> become very difficult to exploit.
>
>> As far as I known the EPSG database is the most widely accepted at
>>
> least
>> at OGC. Some other sources like the PostGIS "spatial_ref_sys" table
> are
>> actually generated from a subset of the EPSG database.
>
> The EPSG database will certainly be a large portion of a
> super-dictionary. However, I would like to be able to capture other
> coordinate system dictionaries too.  A few of interest to me:
>
> * The datum list from NGA, as used in GeoTrans.
> * The ESRI "coded" extensions to EPSG.
> * The ERMapper projection and datum definitions.
> * The MapInfo datum list.
> * The IAU (International Astronomical Union) definitions for other
> planets. * OGC authority space definitions like urn:ogc:def:crs:OGC::CRS84
>
>
> I should also point out http://spatialreference.org/ as a point of
> interest in our discussions.  This web site maintains it's own list of CRS
> definitions, many user submitted, though starting from the EPSG set.  It
> effectively stores them internally as WKT (I think) but endevors to return
> them in a variety of formats (using OGRSpatialReference facilities to do
> the translation).
>
>>> - CRS interface spec. (not necesary but would be nice)
>>>
>>
>> GeoAPI ?
>>
>
> When talking about dictionaries I would prefer not to get hung up on
> API specifications.  I'd prefer to manage and provide a dictionary in
> some form suitable exploitation by different packages and leave it to them
> to talk about APIs.
>
> I'm keen on GeoAPI as a basis for shared Java coordinate system
> libraries but I would like to keep that discussion distinct from the
> dictionary discussion if possible.  Obviously starting from an ISO model
> (or
> perhaps a subset of the ISO model) makes it easier to map the dictionary to
>  something like GeoAPI.
>
> Best regards,
> --
> ---------------------------------------+--------------------------------
> ------
> I set the clouds in motion - turn up   | Frank Warmerdam,
> warmerdam at pobox.com light and sound - activate the windows |
> http://pobox.com/~warmerdam
> and watch the world go round - Rush    | President OSGeo, http://osgeo.org
>
>
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-- 
Arnulf Christl
http://www.wheregroup.com