Paragon Corporation schrieb:
What about
http://www.postgis.org/documentation/manual-1.4.1SVN/ST_Line_Substring.html
That would give you a percent of the string.
If you need exact lengths, you could derive the percent by simple math
of 1000/ST_length(the_geom) (would be the fraction you need to give to
startfrac to get the range of the string you want.
Leo
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Daniel
Grum
Sent: Wednesday, September 09, 2009 3:20 PM
To: [email protected]
Cc: PostGIS Users Discussion
Subject: Re: [postgis-users] Make a shorter line from a given line
[email protected] schrieb:
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_le
ngth(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.h
tml
/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
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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
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A very good idea.
I try to understand it..what do you want to solve with:
1-((st_length(geom)-100)/st_length(geom))
should this be a percantage part of the original line...I don't understand
it than.
I think we are on a good way...
--daniel
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I have found the problem--> the_geom has the geometry type
MULTILINESTRING this is a problem in using the functions
ST_Line_SubString() or st_line_interpolate_point(). So if I want to use
this functions I have to change the geo type to LINESTRING ...I solved
this by inserting the function ST_LineMerge() !
So Thanks for the tipps.
--daniel
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