[postgis-users] GML vs SVG {-5.4}

[Sean Montague]

I'm really starting to get the picture, and I like what I see.  Thanks to everyone who has responded.

>>> rkgeorge at cadmaps.com 04/07/04 01:40PM >>>
Hi,
	Getting your map data into PostGIS from svg or any other format requires a
conversion to WKT (possibly WKB also). This allows you to use all the GIS
query capability on a geometry column in your resulting PostGIS table.

	At the other end, to see the map data on a simple browser client would
requires exporting the query result from WKT to svg.

	I can't see any great advantage to exporting from WKT to GML and then using
XSLT to svg. However, I know that the OGC is pushing GML for open transport
between vendors.

	If you have data locked into a specific vendor, GML is a nice thing to have
available, but if you are looking for a simple svg result you would probably
take the GML into PostGIS via WKT and just use svg on the output side.

Randy George


-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net 
[mailto:postgis-users-bounces at postgis.refractions.net]On Behalf Of
Martin Davis
Sent: Wednesday, April 07, 2004 11:51 AM
To: PostGIS Users Discussion
Subject: RE: [postgis-users] GML vs SVG


GML and SVG are not "mutually exclusive" - they are just different
technologies, filling different needs.  GML is designed to be a
convenient, open way of describing geographic data.  SVG is designed to
be an open way of describing vector graphic images.

If you want SVG as your end result, then whether or not you go through
GML entirely depends on how you are building your transformation
pipeline.  People who are building XSLT to transform GML to SVG likely
already have a GML datasource (either raw files or a GML producer such
as WFS).  They are also probably trying to leverage existing tools to
minimize the amount of effort required to build their pipeline.  If you
don't have that as a constraint, then you can simply build a direct
data->SVG pipeline.

Martin Davis, Senior Technical Architect
Vivid Solutions Inc.
Suite #1A-2328 Government Street Victoria, B.C. V8T 5G5
Phone: (250) 385 6040 - Local 308 Fax: (250) 385 6046


> -----Original Message-----
> From: Sean Montague [mailto:SMontague at oaconsulting.com] 
> Sent: April 7, 2004 9:35 AM
> To: postgis-users at postgis.refractions.net 
> Subject: Re: [postgis-users] GML vs SVG {-5.2}
>
>
> This is where I am getting confused.  I read in places that
> people are using xslt to display GML as SVG.  Are these
> people not reading the data from a database?  Storing the
> data as GML and displaying it as SVG.  Which if this is a
> case, then to read directly from a database like postgreSQL
> and PostGIS, GML is a wasted step if the ultimate format is
> SVG.  What I'd really like is a caparison of GML vs SVG, if
> it is appropriate.  SVG is very powerful and I know it well.
> I've written apps that query a MySQL database and have
> customized some tools.   I'm just trying to figure out if I
> should learn GML.  Is there something about GML that is an
> advantage over SVG?  Thanks.
>
> >>> pramsey at refractions.net 04/07/04 10:08AM >>>
> Sean Montague wrote:
> > I have made many a map with SVG, but I'm new to PostGIS.  So new in
> > fact that I haven't even installed it yet.  I've been using
> MySQL, but
> > have come to the conclusion that postgreSQL is the way to
> go. So, for
> > those of you familiar with both SVG and GML, can you explain the
> > relationship between the two, it seems they are not mutually
> > exclusive, and why wouldn't I write directly to SVG if a
> map ends up
> > in SVG anyway?  I'm trying to sort through all this to
> determine the
> > direction I should go in.  Thanks.
>
> If you are determined to write out SVG then certainly GML gives you
> nothing in terms of advantage. If you are building a more generic
> infrastructure, then a WFS (web feature server that serves
> GML) on top
> of your database can provide a nice generic API to your
> underlying data.
>
> --
>        __
>       /
>       | Paul Ramsey
>       | Refractions Research
>       | Email: pramsey at refractions.net 
>       | Phone: (250) 885-0632
>       \_
>
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