[Portugal] Fwd: [GRASS-user] NEW: Raster/vector intersections in PostGIS WKT Raster

[Eloi Ribeiro]

---------- Forwarded message ----------
From: Pierre Racine <Pierre.Racine  sbf.ulaval.ca>
Date: Tue, Jun 29, 2010 at 5:29 PM
Subject: [GRASS-user] NEW: Raster/vector intersections in PostGIS WKT Raster
To: "grass-user  lists.osgeo.org" <grass-user  lists.osgeo.org>


Hi everybody,

I'm pleased to announce that you can now do intersections between rasters
and geometries very much like you used to do geometry/geometry intersections
in PostGIS. For this, PostGIS WKT Raster introduces two new functions to
PostGIS: ST_Intersects(geometry, raster, band) and ST_Intersection(geometry,
raster, band).

As its geometry/geometry sister, ST_Intersects(geometry, raster, band)
returns TRUE if the withvalue area of a raster or a raster tile (nodata
value are ignored) intersects a geometry and ST_Intersection(geometry,
raster, band) returns the geometry/value set of geometries representing the
intersection between the geometry and each polygonized group of pixel
sharing a same value from the raster and its associated value. Example:

SELECT polyid,
      (ST_Intersection(the_geom, rast)).geom,
      (ST_Intersection(the_geom, rast)).val
FROM my_polygons, srtm_tiled
WHERE ST_Intersects(rast, the_geom)

or, a bit more complex, but much faster and returning the same result:

SELECT polyid, (gv).geom, (gv).val
FROM (SELECT polyid, ST_Intersection(the_geom, rast, 1) AS gv
    FROM my_polygons, srtm_tiled
    WHERE ST_Intersects(rast, the_geom)) foo

These functions works with any kind of geometry so you can intersect any
road, river, polygons or point layer with your favorite elevation or land
cover raster of any resolution and any size. You can also load any number of
raster in the database with one command line to constitute a unique table
raster coverage of any shape (no matter if your group of raster do not form
a rectangular coverage).

You will find a complete tutorial on how to use those two new functions
here: http://trac.osgeo.org/postgis/wiki/WKTRasterTutorial01. A reference is
available here:
http://postgis.refractions.net/documentation/manual-svn/RT_reference.htmland
chapter 13 of "PostGIS in Action" is also a very good introduction to
WKT Raster.

Compilation and installation info are available in the project home page:
http://trac.osgeo.org/postgis/wiki/WKTRaster

These features are the result of two years of collaboration between many
people and companies interested in bringing raster into PostGIS. I would
like to thanks particularly Steve Cumming who initially made all this
possible, Sandro Santilli who wrote the base code, Mateusz Loskot who wrote
the Python loader, Jorge Arevalo who wrote the GDAL driver and
ST_DumpAsPolygons(), Regina and Leo Obe who are doing so many things and
believed in the project from the beginning by adding a chapter about WKT
Raster in "PostGIS in Action" and also David Zwarg who wrote most of the
setter functions.

This is the first step toward a first complete raster/vector analysis and
manipulation SQL API. We hope to make of PostGIS with WKT Raster the most
powerful and complete GIS analysis and manipulation high level language ever
(!!!). WKT Raster should normally be totally integrated into PostGIS in
PostGIS release 2.0. Upcoming functions should include ST_Reclass, ST_Clip,
ST_AsRaster, ST_Resample.

Let us know your need and your experience with WKT Raster.

Thanks,

Pierre Racine

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-- 
Eloi Ribeiro
GIS Analyst
39,45º -4,40º
http://eloiribeiro.wordpress.com
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