[postgis-devel] [postgis-users] Split line at a given point

[Kevin Neufeld]

This seems to be a common use case.  Would it make sense to capture 
sequences like this to a function for introduction into PostGIS?  For 
starters, this could be a simple plpgsql function (converted to C at a 
later date if the need arises) that accepts a linestring and a point and 
returns a multilinestring split at the given point. We already have the 
capability of merging linestrings ....

Cheers,
Kevin

Paragon Corporation wrote:
> Shane,
>
> Use
> http://www.postgis.org/documentation/manual-svn/ST_Line_Locate_Point.html to
> locate the % position it is on the line,
>
> Then use ST_Line_substring
> http://www.postgis.org/documentation/manual-svn/ST_Line_Substring.html
>
> So for example 
> If you get 0.25 back from ST_Line_Locate_Point
>
> The trick is the answer you get won't be exactly on the line so you then
> need to do a ST_SetPoint on the other part
>
> Then the answer you seek would be
>
> So basically
>
> Pt is the point
>
> Line1 = ST_Line_SubString(the_geom, 0, ST_Line_Locate_Point(the_geom) )
> Line2 = ST_Line_SubString(the_geom, ST_Line_Locate_Point(the_geom), 1)
>
> http://www.postgis.org/documentation/manual-svn/ST_SetPoint.html
>
> --This part is to get around floating point errors to force the two lines to
> connect back at the juncture
> Line2 = ST_SetPoint(Line2,0 , ST_EndPoint(Line1))
>
> Leo
>
>
> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net
> [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Shane
> Butler
> Sent: Monday, October 19, 2009 6:51 PM
> To: PostGIS Users Discussion
> Subject: [postgis-users] Split line at a given point
>
> Hi all,
>
> I am trying to split a linestring into two linestrings at a given
> (intersecting) point.  Can anyone give me a hint?  I have tried
> ST_Difference(mylinestr,mypoint) but it just returns mylinestr...
>
> Im using: "POSTGIS="1.3.5" GEOS="3.0.3-CAPI-1.4.2" PROJ="Rel. 4.6.1,
> 21 August 2008" USE_STATS"
>
> Kind Regards,
> Shane
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