[postgis-devel] issues with line_substring() and 4d lines

[Christoph Spoerri]

strk,

in case you would like some code that does the interpolation, please check out 
the LRS functions I sent to the list a few weeks ago. I implemented the 
function so that they perform interpolation.

Let me know if I can help out in order to get the functionality into the next 
version/release.

cheers,
Christoph

On Wednesday 18 January 2006 05:20, strk at refractions.net wrote:
> Thank you. Fixed in CVS.
> I don't think we'll implement interpolation before next
> release, but that'd be interesting.
>
> --strk;
>
> On Wed, Jan 18, 2006 at 08:06:28AM +0100, Alex Mayrhofer wrote:
> > Hi,
> >
> > it seems to me as if there is a bug in line_substring() when performing
> > the function on 4D lines:
> >
> > sketch=# select
> > asewkt(line_substring(geomfromewkt('SRID=4326;LINESTRING(0 0 0 0, 1 1 1
> > 1, 2 2 2 2, 3 3 3 3, 4 4 4 4)'), 0.5, 0.8));
> >
> >                       asewkt
> > ---------------------------------------------------
> >  SRID=4326;LINESTRING(2 2 0 0,3 3 2 2,3.2 3.2 0 0)
> > (1 row)
> >
> > Please note the third output value - there is a problem with the Z and M
> > value (i'd assume them to be 0 as well) [it looks like a copy of the
> > previous points corrdinates).
> >
> > I can reproduce similar issues with more complex geometries as well:
> >
> > SRID=4326;LINESTRING(16.3116663381532 48.1343234522231 0 0,16.311761
> > 48.134512 16.311517 48.134026,16.31199 48.135002 16.311761
> > 48.134512,16.311828 48.135112 16.31199 48.135002,16.311463 48.135228
> > 16.311828 48.135112,16.311485 48.135325 16.311463 48.135228,16.311978
> > 48.135789 16.311485 48.135325,16.312465 48.136218 16.311978
> > 48.135789,16.312534 48.136492 16.312465 48.136218, ...
> >
> > (original Z and M contain altitude and ctime, so those output values are
> > for sure out of range of the input values, and seem to originate from X
> > and Y values).
> >
> > Additionally, a question: are there any plans to extend the various
> > linear referencing functions to also interpolate Z (and optionally M)
> > values?
> >
> > thanks,
> >
> > Alex
> > ---
> > http://nona.net/features/map/
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