[postgis-users] ST_Raster question, Use spot heights and create an Elevation raster layer

[Ed Linde]

Thanks Pierre,

*SELECT o.osm_id,
   ST_AsText((ST_Intersection(ST_Transform(o.way,4326), s.rast)).geom),
   (ST_Intersection(ST_Transform(o.way,4326), s.rast)).val
 FROM planet_osm_line o,
   srtm_tiled_4326 s
 WHERE ST_Intersects(ST_Transform(o.way,4326), s.rast)
 and   o.highway = 'primary';

osm_id; intersecting linestring, elevation (mts)
16815326;"LINESTRING(8.58333333333333 56.2074149493615,8.58261220053766
56.2066666666667)";45*
*..*
*..*
I get to see the elevation now for my geometry and raster. I now want to
introduce some artificial points that
are equidistant (say 10 mts apart) on each road segment.. and then compute
their intersection with the raster.
Is it better to first divide the lines into such points and then compute
their intersections with the raster? Or
break the linestring that I get back after intersection? I have an idea of
how I might be able to do this, but
just wanted to confirm what will perform better.

Cheers,
Ed
*
*
*
*
On Tue, Feb 28, 2012 at 4:28 PM, Pierre Racine
<Pierre.Racine at sbf.ulaval.ca>wrote:

> > What I wish to now do is to use those spot heights to create an
> elevation raster
> > layer via which all NoDataValued pixels have an elevation set that is
> interpreted
> > from the spot heights around it.
> >
> > Has anyone any suggestions as to how this can be done by PostGIS's
> ST_Raster?
> > (ST_MapAlgebra perhaps etc?)
>
> We don't have any interpolation algorithm yet. But we have
> ST_MapAlgebraFctNgb() which compute pixels value as focal functions (or
> moving windows). I not sure to which degree you can implement interpolation
> with moving windows but if your points are close to each other enough you
> could compute the mean of the point surrounding each point. Have a look at:
>
>
> http://postgis.refractions.net/documentation/manual-svn/RT_ST_MapAlgebraFctNgb.html
>
> Pierre
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