[postgis-users] vector layer manipulation

[Nicolas Ribot]

Hi,

st_dumppoints will do that.

Nicolas

On 24 June 2012 13:52, chathura silva <chathurait at gmail.com> wrote:
> suppose you are given the co-ordinates of starting and end points of a road
> segment.
> Is there any way to extract the other set of co-ordinates laying on the road
> segment
> ?
>
> An example +++++++++++++
>
> Here's an approach using Spatialite:
> You can use the spatialite functions DissolvePoints() or DissolveSegments()
> to get each point or line segment along a LINESTRING. Here's an example:
>
> (I created  in advance a sample LINESTRING called 'seg')
> PRAGMA table_info("seg");
> 0    pk_uid    integer    0    NULL    1
> 1    label    text    0    NULL    0
> 2    Geometry    LINESTRING    0    NULL    0
>
> SELECT * FROM seg;
> 1    a    BLOB sz=176 GEOMETRY
> 2    b    BLOB sz=112 GEOMETRY
>
> (I have two simple LINESTRINGs)
> SELECT AsText(Geometry) FROM seg;
> LINESTRING(1 1, 2 1, 2 2, 3 2, 4 2, 5 3, 6 2, 7 1)
> LINESTRING(2 2, 2 4, 4 4, 5 2)
>
> Now, I want to choose one of the linestrings, based on it's start and end
> points:
> SELECT AsText(Geometry) FROM seg
>     WHERE StartPoint(Geometry) = GeomFromText('POINT(1 1)', 4326) AND
>                     EndPoint(Geometry) = GeomFromText('POINT(7 1)', 4326);
> LINESTRING(1 1, 2 1, 2 2, 3 2, 4 2, 5 3, 6 2, 7 1)
>
> and to break up the LINESTRING into its segments:
> SELECT AsText(DissolveSegments(Geometry)) FROM seg
>     WHERE StartPoint(Geometry) = GeomFromText('POINT(1 1)', 4326) AND
>         EndPoint(Geometry) = GeomFromText('POINT(7 1)', 4326);
> MULTILINESTRING((1 1, 2 1), (2 1, 2 2), (2 2, 3 2), (3 2, 4 2), (4 2, 5 3),
> (5 3, 6 2), (6 2, 7 1))
>
>
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