Re: [georss] Scaling/size of geographical entities

The following is provided as input - not a solution

As an FYI, the OASIS Emergency Management TC had a lengthy discussion about 
how to handle a circle in their CAP and EDXL standards. The final decision 
was a major compromise for version 1.0 of CAP. They wanted a really simple 
expression of a circle by center point and radius. However, given the 
limitations of this approach, the next version will provide the ability to 
use GML to express geometry, including circles.

And this issue is huge for the location services infrastructure providers. 
In the latter case, they do not use circles for exactly the reason Ron 
points out. When using a Lat/Long CRS, circles become ellipses when 
displayed or even more interesting shapes as one approaches the poles.

Then there are issues related to units of measure. Is the radius in 
kilometers, miles, feet? This is why Ron's example show the use of uom 
(Units of Measure). Dealing with the use and display of lat/long coordinates 
can be so problematic, Federal agencies such as the EPA have developed 
internal standards for dealing with these coordinates! 
http://www.epa.gov/edr/flatlongbr.pdf

Why say all of this? Well, if we extend the vocabulary to other geometries 
and properties for those geometries, we will immediately encounter 
discussion issues whose resolution will require careful documentation as 
part of the GeoRSS definition to insure unambiguous semantics.

Sorry, the Geographer/Cartographer in me is showing :-)

Regards

Carl

----- Original Message ----- 
From: "Ron Lake" <rlake@galdosinc.com>
To: "Allan Doyle" <adoyle@eogeo.org>; "Andrew Turner" 
<georss@highearthorbit.com>
Cc: <public-xg-geo@w3.org>; <georss@lists.eogeo.org>; "Holger Knublauch" 
<holger@topquadrant.com>
Sent: Friday, July 21, 2006 3:29 PM
Subject: RE: [georss] Scaling/size of geographical entities


>
> Hi,
>
> There is a CircleByCenterPoint in GML which has a center point and
> radius.
>
> <gml:CircleByCenterPoint>
> <gml:pos>45.256 -110.45</gml:pos>
> <gml:radius uom="#meters">500</radius>
> </gml:CircleByCenterPoint>
>
>
> Of course there will be issues of the meaning of this when placed into a
> non-flat manifold - but for flat earth's this is ok.
>
> R
>
> -----Original Message-----
> From: georss-bounces@lists.eogeo.org
> [mailto:georss-bounces@lists.eogeo.org] On Behalf Of Allan Doyle
> Sent: July 21, 2006 1:54 PM
> To: Andrew Turner
> Cc: public-xg-geo@w3.org; georss@lists.eogeo.org; Holger Knublauch
> Subject: Re: [georss] Scaling/size of geographical entities
>
> I think radius is in dispute... I forget who likes it and who does
> not. The issue, as far as I recall, is that GML does not have a
> circle that's defined by a point and a radius so GeoRSS Simple can't
> have one.
>
> Allan
>
> On Jul 21, 2006, at 16:43, Andrew Turner wrote:
>
>> Holger Knublauch  wrote:
>>>
>>> Thanks Joshua.  With a basic glimpse on this, I would hope that
>>> the geo
>>> ontology is extended with a geo:radius attribute: it is a low hanging
>>> fruit while having feature types is probably an overkill.  To specify
>>
>> There is a radius in GeoRSS Simple:
>>
>>   <georss:point radius="500">45.256 -110.45</georss:point>
>>
>> It was at the bottom of the "Simple" page, so maybe you missed it. :)
>> Andrew
>>
>> -- 
>> Andrew Turner
>> ajturner@highearthorbit.com        42.4266N x 83.4931W
>> http://highearthorbit.com              Northville, Michigan, USA
>> _______________________________________________
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>> georss@lists.eogeo.org
>> http://lists.eogeo.org/mailman/listinfo/georss
>
> -- 
> Allan Doyle
> +1.781.433.2695
> adoyle@eogeo.org
>
>
>
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>

Received on Friday, 21 July 2006 22:34:59 UTC