[postgis-users] Midpoint function?

[Pradeep B V]

On 6/21/07, Rodrigo Martín LÓPEZ GREGORIO <rodrigomlg at gmail.com> wrote:
>
> Hi Pradeep
>
> I don't know what you exactly mean by midpoint of a MULTILINESTRING. If
> what you are looking for is the point on the multilinestring located half
> way on a imaginary linestring that have the total length of the
> MULTILINESTRING and is formed by sewing together constituent linestrings I
> can write a function that do this.


Yes. this is what I am looking for.

Must it fill the gaps between end point of first linestring and start point
> of second linestring (i.e. consider the space between consecutive
> linestrings as part of this imaginary linestring)?


The dataset that I have doesn't have any gaps between linestrings that make
up the multilinestring. Here is a sample:
MULTILINESTRING((77.6177520751953 12.8762445449829,77.6180953979492
12.8769254684448,77.6182174682617 12.8771991729736,77.6182708740234
12.877254486084,77.6
183853149414 12.877293586731,77.6186065673828 12.8773241043091,
77.6188049316406 12.8773641586304,77.6189193725586 12.8774423599243,
77.6190490722656 12.877568
2449341,77.6192092895508 12.8777647018433,77.6192932128906 12.8778190612793,
77.6194458007812 12.8778419494629,77.6196899414062 12.8778429031372,
77.6200714111
328 12.8777952194214,77.6207504272461 12.8777093887329,77.6210403442383
12.8776388168335,77.6211013793945 12.8775682449341,77.6212387084961
12.8774185180664,
77.6214828491211 12.87730884552,77.6220855712891 12.87717628479,
77.6224746704102 12.877121925354,77.6232223510742 12.8771133422852,
77.6239013671875 12.877034
1873169,77.6239318847656 12.8770303726196))

which is actually a continuous line. The only reason this got in as a
Multilinestring is because the  the original shapefile provided to
shp2pgsql  was having Multilinestrings as the default data type.

If you have any other detail about the function you want tell me.


Thanks in advance.

- Pradeep

>
> On 6/21/07, Pradeep B V <pradeepbv at gmail.com> wrote:
> >
> > Is there any other function equivalent to the line_interpolate_point(the_geom,
> > 0.5) to find the midpoint of a MULTILINESTRING?
> >
> > the line_interpolate_point works only with LINESTRINGS.
> >
> > - Pradeep B V
> > www.btis.in
> >
> >
> > On 6/21/07, Rodrigo Martín LÓPEZ GREGORIO <rodrigomartin at lopezgregorio.com.ar>
> > wrote:
> > >
> > > Hi Matt.
> > >
> > > I think what you want may be:
> > >
> > > line_interpolate_point(the_geom,0.5)
> > >
> > > (or ST_line_interpolate_point(the_geom,0.5) depending on your Postgis
> > > version)
> > >
> > > where the_geom is a linestring and 0.5 means half of the total 2d
> > > length of the linestring.
> > >
> > > You can reed more details in the documentation:
> > >
> > > http://postgis.refractions.net/docs/ch06.html#line_interpolate_point
> > >
> > > Rodrigo
> > >
> > > On 6/21/07, Matt Doughty < matt.doughty at geograma.com> wrote:
> > > >
> > > >  Hi List,
> > > >
> > > >
> > > >
> > > > Is there a function in PostGIS that finds the midpoint of a line?
> > > >
> > > >
> > > >
> > > > Matt
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > Matt Doughty
> > > >
> > > >   GEOGRAM A S.L.
> > > >
> > > > Tel.:  +34 945 13 13 72    652 77 14 15
> > > >
> > > > Fax: +34 945 23 03 40
> > > >
> > > > www.geograma.com
> > > >
> > > >
> > > >
> > > >
> > > >
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