[postgis-users] line from points (& feature manipulation/editing)

[pinktomate]

GREAT
but the function line from point is not defined in postgis 0.8.2

I might be wrong¿?¿?

El mar, 05-10-2004 a las 02:58, strk at refractions.net escribió:
> On Tue, Oct 05, 2004 at 12:02:54AM -0700, Wood Brent wrote:
> > 
> > --- strk at refractions.net wrote:
> > 
> > > > 
> > > > how I can to create a line or polyline  from a collection of points with
> > > > coordinates, inside of postgis of course
> > > 
> > > This is an unavailable feature, being discussed.
> > > How would you specify the ordering of the composing points ?
> > 
> > Summat I'm also interested in, improved feature editing & manipulation in
> > PostGIS, building lines from points, assembling polygons from lines, merging
> > polygons by removing shared borders, splitting polygons by inserting a new
> > line, etc....
> 
> Isn't "merging polygons" already implemented by GeomUnion ?
> 
> > 
> > At present, I believe GRASS 5.7 is perhaps the best tool for this? JUMP/JTS is
> > also there, but doesn't do what I need. QGIS may get there, it is certainly
> > adding functionality quite rapidly. 
> > 
> > Is there a way to have PostGIS use something like the JTS natively, much as it
> > uses GEOS now, to implement such capabilities?
> 
> mmm. what do you mean by natively ?
> GEOS is a JTS port. Everything available in JTS can be made available
> in PostGIS.
> 
> > 
> > But to specify the line vertex order from point features, you would need some
> > attribute(s) to provide an explicit order. In many cases I work with, this
> > could be a timestamp, to turn a set of stations into a track.
> > 
> > ie: something like 
> > 
> > select linefrompoint(the_geom) where <...> order by <ordering_attr(s)>
> > 
> > to create a line from a set of points selected & ordered from a table of
> > points.
> > (unless I'm missing something...) 
> 
> Yes. You're missing that ORDER BY acts on the result set, which in this
> case is a single record.
> If you want to use it to order aggregate input you should do:
> 
> SELECT linefrompoint(
> 	(SELECT the_geom FROM <table> ORDER by <ordering_attr(s)>)
> );
> 
> Which is use a subselect to feed ordered values to the aggregate.
> 
> --strk;
> 
> > 
> > 
> > 
> > & I second the thanks for both PostGIS itself & the help from this forum!!
> > 
> > 
> > Cheers,
> > 
> >   Brent Wood
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