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<TITLE>RE: [postgis-users] RE: [postgis-devel] GML and XY,XYM,XYZ,XYZM</TITLE>
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<DIV><FONT size=2>Darko,</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>The M here is nothing to do with SVG. It is a
"measure", e.g. along a linear geometry or along the perimeter of a polygonal
geometry, hence Linear Referencing System.</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>Regards,</FONT></DIV>
<DIV><FONT size=2>Martin</FONT></DIV>
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<DIV><FONT size=2>-----Original Message----- <BR><B>From:</B> Darko Androsevic
[mailto:dandrosevic@galdosinc.com] <BR><B>Sent:</B> Wed 06/10/2004 19:31
<BR><B>To:</B> 'PostGIS Users Discussion'; 'PostGIS Development Discussion'
<BR><B>Cc:</B> Ron Lake (E-mail); David Burggraf (E-mail) <BR><B>Subject:</B>
RE: [postgis-users] RE: [postgis-devel] GML and
XY,XYM,XYZ,XYZM<BR><BR></FONT></DIV>
<P><FONT size=2>Hello,<BR><BR>GML has no way to emulate M, L or other special
characters used in SVG for<BR>drawing the shape. GML should be used to
describe geometries.<BR><BR>GML provides NO support (except deprecated
support) for explicit coordinate<BR>tags and this will not come back in
GML.<BR>We would recommend to use the <gml:pos> element in combination
with the CRS<BR>("srsName" attribute) to desribe the coordinates of the
geometries. The<BR><gml:coord> element should not be supported in any
new softwares.<BR><BR>Thanks,<BR>Darko<BR><BR><BR><BR>-----Original
Message-----<BR>From: postgis-users-bounces@postgis.refractions.net<BR>[<A
href="mailto:postgis-users-bounces@postgis.refractions.net">mailto:postgis-users-bounces@postgis.refractions.net</A>]On
Behalf Of<BR>strk@refractions.net<BR>Sent: Wednesday, October 06, 2004 3:17
AM<BR>To: PostGIS Development Discussion; PostGIS Users Discussion<BR>Subject:
Re: [postgis-users] RE: [postgis-devel] GML and XY,XYM,XYZ,XYZM<BR><BR><BR>On
Wed, Oct 06, 2004 at 10:37:28AM +0100, Martin Daly wrote:<BR>>
strk,<BR>><BR>> > I've introduced support for XYM.<BR>> > How
should XYM geometries be rendered in GML ?<BR>> > And what aboux XYZM
?<BR>><BR>> Excellent questions, with no easy answers.<BR>><BR>>
GML 2.x <coord> elements are hard-wired to have elements <X>,
<Y> and<BR>> <Z>, so that is a non-starter. GML 2.x
<coordinates> elements just<BR>> contains tuples of co-ordinates, so
that is a possibility. I very much<BR>> doubt that any existing GML
2.x parsers have any knowledge of linear<BR>> reference systems, and
instead assume that the tuples have at most three<BR>> ordinates, and that
they are X, Y and optionally Z. Other usage is<BR>> valid, but
is likely to be restricted to a particular vendor, or<BR>> industry, or
whatever, and is not likely to be particularly<BR>>
interoperable.<BR>><BR>> GML 3.x has more support for specifying the CRS
of the tuples, including<BR>> linear reference systems, but using that will
reduce the number of<BR>> available clients for the data, because GML 3
support is not widespread.<BR>><BR>> Not only no easy answers, but no
answers at all! Would it be tolerable<BR>> to not support AsGML for
XYM and XYZM, or to strip the M?<BR><BR>Sure.<BR>Current implementation
uses:<BR> GML:XY for XY and
XYM (strips the M)<BR> GML:XYZ for
XYZ and XYZM (strips the M)<BR>thanks for the
info.<BR>--strk;<BR><BR>><BR>> Regards,<BR>> Martin<BR>>
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