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

[strk at refractions.net]

On Tue, Oct 05, 2004 at 10:59:56AM -0500, pinktomate wrote:
> GREAT
> but the function line from point is not defined in postgis 0.8.2
> 
> I might be wrong¿?¿?

You're right. And it is not defined in postgis 0.9 too.
Maybe 1.0 will have it...
--strk;


> 
> 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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