Subject: Re: GEO question

From: "John Rose" <[email-masked]>
Date: Wed, 16 Feb 2000 12:14:44 -0800

As I understand your question, you want to know the details of the
map projection (which uses datum, hemisphere, offset, etc.) to be
used for the GEO property.  However, the GEO property is defined
as being expressed in latitude/longitude, which is a spherical
coordinate system and NOT a map projection.

If you have a location coordinate that's currently expressed in some
map projection (e.g. Albers, Robinson, etc.), you must convert that
projection to the standard non-projected lat/lon coordinate space
in order to assign it to the GEO property.  Conversely, to use a GEO
property that you've received, you MAY need to convert it to whatever
projection is being used by your GIS application/data.

Note also that the lat/lon coordinates for the GEO property are
in "decimal degrees", rather than in a degrees-minutes-seconds
format.  RFC2445 provides the exact formula for generating the
decimal degrees value used by the GEO property.

The Federal Information Processing Standard was mentioned for
completeness, but my recollection is that it's long, boring and
very confusing, and not typically useful unless there's some very
exact detail which almost nobody should every need for the
general purpose of the GEO property (which is to provide the
approximate location of a given meeting).

I hope this answers your question.  If not, please email me
directly with any further questions.

- JR

- -
John Rose
Altawave, Inc.
[email-masked]
[email-masked]

---------------

Pär-Lannerö wrote (on Wed, 16 Feb 2000 11:48:27 +0100 (MET)):

>
> Hello!
>
> We would like to get some more information concerning the GEO
> property. In order for us to be able to use the GEO coordinates in a
> GIS application we need to know what coordinate system to use. Ie.
> what geographic datum, hemisphere, offset etc. The information seems
> to be missing in RFC2445 (perhaps it's in the "Federal Information
> Processing Standard 70-1, but where do I get _that_?).
>
> Thanks!
> /Par (SKiCal project)
>
>
> -Pär-Lannerö----------------------------------------------------------
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