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Subject: Re: [emergency] Groups - CRSRegistry Document by Galdos.doc uploaded

Allen -

I am in Hong Kong this week and as such do not have access to all of my
reference documents. Anyway, a CRS Registry instantiates (in traditional
GIS vernacular) projection parameters that include units of measuremment.
The parameters. What is not seen in the Registry document  is that there
are normative models for both CRS and UOM. These models are both ISO and
OGC standards. These models have been used to create informative documents
(XML Schema). All of these documents can be found on the OGC website. I
think I have this correct but will not be able to accurately (with proper
references) respond until next weekend).


> Carl: apologize for just now getting back to this, but I needed to take
>  some time to let some of the GIS-related comments and discussions that
>  have been floating around to settle into my head. And while I admit,
> as  I have done many times before, I am not GIS expert, I *think* I am
> able  to understand the purpose and idea behind this document. As such,
> I had  a question.
> In terms of how the Units of Measures are created, which if I
> understand correctly are used to create a given CRS, I am curious as to
>  why these units (meter, degrees, etc.) where not defined as derived
> data types? It would seem that by having a UOM dictionary, which would
> be essentially a given CRS, that was nothing more than a list of these
> data types, one could simply reference, through Namespaces, that UOM
> dictionary in instance documents to therefore accomplish the same thing
>  - rather than defining your own referencing scheme (srsName,
> codeSpace,  etc.). Or, if the author of a given XML dialect, such as
> our authoring  of CAP, wanted to explicitly specify which CRS' that
> were allowed, we  would only need to import the applicable UOM
> dictionary(ies) to do  that.
> Just wondering if I was misunderstanding something, as it seemed to me
> the same thing could be accomplished by simply using some of the
> features of XML Schema.
> Allen
> On Apr 10, 2004, at 4:42 PM, creed@opengis.org wrote:
>> The EM TC requested more information about how the OpenGIS Consortium
>> specifies coordinate reference systems (CRS). This request was in
>> relationship to CAP. This document provides basic information about
>> the prototype OGC CRS registry and how an application or encoding can
>> reference this registry.

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