[gdal-dev] Raster/vector intersections in PostGIS WKT Raster

[christian.mueller at nvoe.at]

Hi, superb job. Congratulations.

I am a geotools/geoserver developer and one of my jobs is fetching  
image tiles  or the corresponding pyramid tiles from jdbc data  
sources. Some weeks ago, I added support for Oracle Georaster and I  
want to support WKT Georaster too.

wktraster makes it quite simple to achieve this. Is there any database  
layout you recommend. (A table for the image and one for each pyramid,  
or put all the tiles into one table having an attribute "level",.....).

I have seen "gdal2wktraster.py", is this the recommended way to import  
tiles into postgis ?
What is the table layout created/needed by this utility ?

Cheers
Christian



Quoting Pierre Racine <Pierre.Racine at sbf.ulaval.ca>:

> 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.html   
> and 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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>



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