[postgis] GML vs. WKT

[mbdavis]

As Frank said, WKT predates GML, and yes, it does separate coordinates with
a space and points with a comma.  This syntax is defined in the OGC Simple
Features for SQL specification
(http://www.opengis.org/techno/specs/99-049.pdf).

In actual fact, the GML spec doesn't restrict coordinate and point
separators to be commas and spaces - it allows the user to specify the
separators (see http://www.opengis.net/gml/01-029/GML2.html#sec4.3).
Whether anyone should make use of this flexibility is another question.
Personally, I think not - the more flexible the specification, the more
complex parsers have to be. 

While the difference is unfortunate, as you say it only makes life
*slightly* more complex for translator developers.  Also, no matter what the
extra effort required, the work in writing a WKT-to-GML translator is far
less than in writing any <binary spatial format>-to-GML translator.

Martin Davis, Senior Technical Specialist
Vivid Solutions Inc.
Suite #1A-2328 Government Street   Victoria, B.C.   V8T 5G5
Phone: (250) 385 6040    Fax: (250) 385 6046
EMail: mbdavis at vividsolutions.com  Web: www.vividsolutions.com

>  -----Original Message-----
> From: 	Rob Hranac [mailto:robhranac at vfny.org] 
> Sent:	Thursday, February 14, 2002 6:16 PM
> To:	postgis at yahoogroups.com
> Subject:	[postgis] GML vs. WKT
> 
> Hi Guys,
> 
> I have a question about the syntax of your geometry 
> functions.  Example:
> GeometryFromText('LINESTRING(191232 243118,191108 243242)',-1)
> 
> You mention that this is the WKT description of OGC 
> primitives.  Note that your geometry functions separate 
> coordinates by a space delimiter and coordinate tuples by a 
> comma delimiter.  This is the exact opposite of common 
> practice in the GML world.  Although GML allows you to 
> specify any delimiter you want for each (in the 'ts' and 'cs' 
> attributes of the <coordinates> element), the default is that 
> coordinates are separated by commas and points/tuples by 
> spaces.  I know almost nothing about WKT (and a quick search 
> on the pristinely organized OGC website showed nothing), but 
> is the default syntax for it's delimiters, then, the exact 
> opposite of GML?
> 
> If not, ignore the rest, but if it is... It is a safe bet 
> that the GML default will become a near-standard in most 
> applications.  Certainly not a show stopper, but it does make 
> life slightly more difficult GML converters such as myself; 
> it is probably a fair assumption that GML converters will 
> someday comprise a large portion of your user base.  Given, 
> this you might think about switching your delimiters, unless 
> I am missing something in WKT or OGC SQL.  
> 
> Remain a big Postgis fan, by the way.  Will soon spam this 
> list with a beta announcement for my open source WFS, which 
> serves exclusively from Postgis.  It is getting tested in 
> OWS1 and Postgis is holding up really well.
> 
> Regards,
> Rob Hranac
> Vision for New York
> 377 Broadway
> NY, NY  10013
> tel: 212.219.6052
> fax: 212.219.6006
> eml: robhranac at vfny.org
> web: www.vfny.org
> 
> 
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