Subject: [Geopriv] geospatial coordinates in pidf-lo document

From: Xiaotao Wu <[email-masked]>
Date: Mon, 10 May 2004 20:30:39 -0400 (EDT)

Hi,

I have a question on specifying a geospatial location in a pidf-lo
document.

What can be put in <gml:Point> tag? It could be  <gml:coordinates> or
<gml:pos>. For <gml:coordinates>, the data can be any string. In the
pidf-lo document's example (page 12), it uses two  degree-minute-second
coordinates to represent a point. Should the format of the string be
specified?

For seconds, whether decimal  value is allowed. For example, whether
40:38:37.25N is valid or not?

Also, whether the degree-minute value is allowed? For example,
whether 40:38.134N is valid or not? Some GPS receivers using degree-minute
value.

Can we use <gml:pos> tag in pidf-lo document? If we can, can someone
provide an example on how to use <gml:pos> to represent a location
in a pidf-lo XML script?

Thank you!

-Xiaotao

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Name      : Xiaotao Wu
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---

From: "Hannes Tschofenig" <[email-masked]>
Date: Tue, 11 May 2004 16:01:07 +0200

hi xiaotao, 

pidf-lo specifies that gml has to be used as the default location
information format. it also says that the functionality provided by
feature.xsd has to be used. gml offers more than feature.xsd. in slide # 3
of http://www.tschofenig.priv.at/geopriv/IETF58/LO_and_GML_Issues_ietf58.ppt you
can find the xml schemas imported by feature.xsd. this gives you a hint
about functionality.

hence, you can described the location of entities in a number of ways. the
point structure is only one possible mechanism. linestring, linearring,
polygon or a box are other possible types. 

the interpretation of the values is left to the coordinate reference system
(crs). you can specify the crs in the srsName attribute of the corresponding
element. hence, it is not an arbitrary string. 

regarding the example in the pidf-lo document which uses coordinates in the
example. 
yes, you can use pos or pointRep instead.  

ciao
hannes

> -----Original Message-----
> From: Xiaotao Wu [mailto:[email-masked]] 
> Sent: Dienstag, 11. Mai 2004 02:31
> To: [email-masked]
> Cc: Xiaotao Wu
> Subject: [Geopriv] geospatial coordinates in pidf-lo document
> 
> Hi,
> 
> I have a question on specifying a geospatial location in a 
> pidf-lo document.
> 
> What can be put in <gml:Point> tag? It could be  
> <gml:coordinates> or <gml:pos>. For <gml:coordinates>, the 
> data can be any string. In the pidf-lo document's example 
> (page 12), it uses two  degree-minute-second coordinates to 
> represent a point. Should the format of the string be specified?
> 
> For seconds, whether decimal  value is allowed. For example, 
> whether 40:38:37.25N is valid or not?
> 
> Also, whether the degree-minute value is allowed? For 
> example, whether 40:38.134N is valid or not? Some GPS 
> receivers using degree-minute value.
> 
> Can we use <gml:pos> tag in pidf-lo document? If we can, can 
> someone provide an example on how to use <gml:pos> to 
> represent a location in a pidf-lo XML script?
> 
> Thank you!
> 
> -Xiaotao
>

---

From: Henning Schulzrinne <[email-masked]>
Date: Tue, 11 May 2004 14:35:38 -0400

More general remark:

It seems less than ideal from an interoperability perspective to have to 
support 548 pages worth of general GIS functionality to identify the 
point location of a presentity, with essentially two or three floating 
point numbers as useful information. Having the general functionality is 
nice, but it might be helpful to describe one suggested way of 
representing presentity locations. Having one implementation do this as 
a polygon, another as a feature, the third as coordinates, the fourth as 
<pos> is never going to yield an interoperable system. I'd be surprised 
if these were the only ways of presenting a point object...

Can we draft the help of some GML experts to find *one* suggested way 
for this application, while not ruling out other applications and more 
general usage?

Henning