It sounds like you could use the linear referencing capability, along the lines of (untested, just off the top of my head)...
select makeline(st_line_interpolate_point(geom,1-((st_length(geom)-100)/st_length(geom))),endpoint(geom)) ie, make you new line the percentage along the original line required by your offset for the start point, and the endpoint remains the same. HTH, Brent Wood --- On Thu, 9/10/09, Daniel Grum <[email protected]> wrote: > From: Daniel Grum <[email protected]> > Subject: Re: [postgis-users] Make a shorter line from a given line > To: [email protected] > Cc: "PostGIS Users Discussion" <[email protected]> > Date: Thursday, September 10, 2009, 5:50 AM > [email protected] > schrieb: > > look at st_scale > > http://www.postgis.org/documentation/manual-1.4.1SVN/ST_Scale.html > > or maybe st_transscale > > http://www.postgis.org/documentation/manual-1.4.1SVN/ST_TransScale.html > > /Nicklas > > > > 2009-09-08 Daniel Grum wrote: > > > > Hy, > > > > > >I want to make a new line from a given line > -->both geometry types are > > >MULTININESTRING > > > > > >Every step the new line should be "x meters" > shorter than the original. > > > > > >I get the length of the line, f.e. 5000 meters > (length(the_geom)) and > > >after the step the new Line should be only 4000 > meters. > > > > > >I have a idea but it isn't ready: > > > > > >UPDATE table > > >SET the_geom = (SELECT > MakeLine(StartPoint(line.the_geom), > > >EndPoint(line_merge(line.the_geom))) > > > FROM public.table line > > > ORDER BY line.gid); > > > > > >But in if I do so I have no chance to say that the > new line has to be > > >100meters shorter than the original line. > > > > > >Are there any ideas how I can solve this problem? > > > > > >Thanks, > > >--Daniel > > >_______________________________________________ > > >postgis-users mailing list > > >[email protected] > > >http://postgis.refractions.net/mailman/listinfo/postgis-users > > > > > > > That is not what I'm searching for. > > Becaus the line lies somewhere in the 2D space and the end > point of the line anytime will be the same in my case...only > the starting point should be changed. > And it should be changed automaticly, step by step, and the > new starting point hvave to be on the old > line/route-->like a route in a map and every time step > the route will be shorter, because the unit has solved x > meters. > > Do you know what I mean? > > Scale and TransScale isn't the right finction I think. > --daniel > _______________________________________________ > postgis-users mailing list > [email protected] > http://postgis.refractions.net/mailman/listinfo/postgis-users > _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
