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List: postgis-users
Subject: Re: [postgis-users] ST_StartPoint() for MultiLineStrings
From: Martin Davis <mtnclimb () telus ! net>
Date: 2012-09-27 15:06:38
Message-ID: 50646B7E.8050500 () telus ! net
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In which case why not just extend ST_StartPoint to include this
behaviour? Always nicer to keep the function list as short as possible.
On 9/27/2012 7:31 AM, David William Bitner wrote:
> Perhaps to match a number of people's expectations, there should be an
> ST_First Point() that is basically
> ST_StartPoint(ST_GeometryN(ST_Multi(geometry),1))
>
>
>
> On Tue, Sep 25, 2012 at 4:08 PM, Paul Ramsey <pramsey@opengeo.org
> <mailto:pramsey@opengeo.org>> wrote:
>
> When ST_NumGeometries == 1, you can run ST_StartPoint on
> ST_GeometryN(geom,1). Where ST_NumGeometries > 1 you are in
> "interpretation land". What's the start point of a geometry with two
> lines?
>
> P.
>
> On Tue, Sep 25, 2012 at 1:38 PM, David Quinn
> <daithiquinn@gmail.com <mailto:daithiquinn@gmail.com>> wrote:
> > As ST_StartPoint( multilinestring ) returns NULL for PostGIS 2.0
> > (http://postgis.refractions.net/docs/ST_StartPoint.html ), what
> > approach can be used to identify the start and end points of a
> > multilinestring?
> >
> > Thanks,
> > David
> > _______________________________________________
> > postgis-users mailing list
> > postgis-users@postgis.refractions.net
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>
>
>
> --
> ************************************
> David William Bitner
>
>
> _______________________________________________
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>
>
> No virus found in this message.
> Checked by AVG - www.avg.com <http://www.avg.com>
> Version: 2012.0.2221 / Virus Database: 2441/5293 - Release Date: 09/26/12
>
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In which case why not just extend ST_StartPoint to include this
behaviour? Always nicer to keep the function list as short as
possible.<br>
<br>
<div class="moz-cite-prefix">On 9/27/2012 7:31 AM, David William
Bitner wrote:<br>
</div>
<blockquote
cite="mid:CAEqvsZsUbzmG__RxNBeA40Y49Qr9ph-ktgtdibiaJspdN6hELQ@mail.gmail.com"
type="cite">Perhaps to match a number of people's expectations,
there should be an ST_First Point() that is basically
ST_StartPoint(ST_GeometryN(ST_Multi(geometry),1))
<div><br>
</div>
<div><br>
<br>
<div class="gmail_quote">On Tue, Sep 25, 2012 at 4:08 PM, Paul
Ramsey <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:pramsey@opengeo.org" \
target="_blank">pramsey@opengeo.org</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">When
ST_NumGeometries == 1, you can run ST_StartPoint on<br>
ST_GeometryN(geom,1). Where ST_NumGeometries > 1 you are
in<br>
"interpretation land". What's the start point of a geometry
with two<br>
lines?<br>
<span class="HOEnZb"><font color="#888888"><br>
P.<br>
</font></span>
<div class="HOEnZb">
<div class="h5"><br>
On Tue, Sep 25, 2012 at 1:38 PM, David Quinn <<a
moz-do-not-send="true"
href="mailto:daithiquinn@gmail.com">daithiquinn@gmail.com</a>>
wrote:<br>
> As ST_StartPoint( multilinestring ) returns NULL
for PostGIS 2.0<br>
> (<a moz-do-not-send="true"
href="http://postgis.refractions.net/docs/ST_StartPoint.html"
target="_blank">http://postgis.refractions.net/docs/ST_StartPoint.html</a>
), what<br>
> approach can be used to identify the start and end
points of a<br>
> multilinestring?<br>
><br>
> Thanks,<br>
> David<br>
> _______________________________________________<br>
> postgis-users mailing list<br>
> <a moz-do-not-send="true"
href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a><br>
> <a moz-do-not-send="true"
href="http://postgis.refractions.net/mailman/listinfo/postgis-users"
target="_blank">http://postgis.refractions.net/mailman/listinfo/postgis-users</a><br>
_______________________________________________<br>
postgis-users mailing list<br>
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href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a><br>
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href="http://postgis.refractions.net/mailman/listinfo/postgis-users"
target="_blank">http://postgis.refractions.net/mailman/listinfo/postgis-users</a><br>
</div>
</div>
</blockquote>
</div>
<br>
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<div><br>
</div>
-- <br>
************************************<br>
David William Bitner<br>
</div>
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<p class="" avgcert""="" color="#000000" align="left">No virus
found in this message.<br>
Checked by AVG - <a moz-do-not-send="true"
href="http://www.avg.com">www.avg.com</a><br>
Version: 2012.0.2221 / Virus Database: 2441/5293 - Release Date:
09/26/12</p>
</blockquote>
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