[postgis-users] [postgis-devel] RFQ: WKT Raster SQL API for being able to intersect vector and raster tables

[Paragon Corporation]

Pierre,

Still busy with getting the stack builder ready, but quickly scanning this,
Leo and I had one question.

It might be a stupid question -- so pelase educate us.

Pierre,
On the ST_Intersects(raster,geometry), ST_Intersection(raster,geometry)

Why do you default the band to #1.  It would seem useful (or at least we
would assume), that if we don't pass in a band number,
that the function would return true/(vector envelope) if any of the bands
intersect with the geometry.  Or is that not of common use or is it just
more computationally intensive?

Thanks,
Regina and Leo



-----Original Message-----
From: postgis-devel-bounces at postgis.refractions.net
[mailto:postgis-devel-bounces at postgis.refractions.net] On Behalf Of Pierre
Racine
Sent: Wednesday, February 10, 2010 10:04 AM
To: PostGIS Development Discussion; (postgis-users at postgis.refractions.net)
Subject: Re: [postgis-devel] RFQ: WKT Raster SQL API for being able to
intersect vector and raster tables

Ok: it should have been "RFC" instead of "RFQ". I don't know what I was
thinking about...

Pierre

>-----Original Message-----
>From: postgis-devel-bounces at postgis.refractions.net 
>[mailto:postgis-devel- bounces at postgis.refractions.net] On Behalf Of 
>Pierre Racine
>Sent: 8 février 2010 13:52
>To: postgis-devel at postgis.refractions.net; 
>(postgis-users at postgis.refractions.net)
>Subject: [postgis-devel] RFQ: WKT Raster SQL API for being able to 
>intersect vector and raster tables
>
>Hi PostGIS folks,
>
>Now that you have a little bit of time after the release of PostGIS 
>1.5, I would like to request your comments on the WKT Raster 
>specifications drawn to meet objective 0.1.6 - "Being able to intersect 
>vector and raster to produce vector". In other word: what set of 
>function do we need to be able to intersect a geometry layer with a 
>raster layer? You will find the last version of the written specs
>here:
>
>http://trac.osgeo.org/postgis/wiki/WKTRaster/SpecificationWork, STing01#Obj
>ective0.1.6e- Beingabletointersectvectorandrastertoproducevector
>
>This kind of operation is a generalisation of the operation needed by 
>many people doing spatial analysis involving raster and vector. Some 
>examples of users expressing their needs for a similar
>functionality:
>
>http://postgis.refractions.net/pipermail/postgis-users/2009-April/02321
>8.html
>
>http://postgis.refractions.net/pipermail/postgis-users/2009-March/02289
>0.html
>
>Some from the r-sig-geo group:
>
>https://stat.ethz.ch/pipermail/r-sig-geo/2009-December/007177.html
>
>https://stat.ethz.ch/pipermail/r-sig-geo/2009-November/006999.html
>
>We plan on reusing as much as possible existing PostGIS functions. The 
>basic idea is to convert (only
>the) WKT Raster tiles involved in the intersect to geometries and then 
>to procede to a normal vector intersection using the PostGIS 
>intersection function. It involves functions like: ST_Envelope(raster), 
>ST_ConvexHull(raster), ST_Shape(raster, integer), ST_AsPolygon(raster, 
>integer), ST_AsWKTPolygon(raster, integer), ST_Intersects(raster, integer,
geometry), ST_Intersection(raster, integer, geometry). Jorge is in charge of
the implementation.
>
>We are now in the process of testing if it is worth using the 
>polygonize function of GDAL, thus linking with GDAL, or implementing 
>our own. A summany of the pros and cons is available at this
>location:
>
>http://trac.osgeo.org/postgis/wiki/WKTRaster/SpecificationWorking01#The
>prosandconsofusingGDALvsimpleme
>ntingourownrasterservices
>
>We are also discussing the pros and cons of directly returning PostGIS 
>geometry objects, thus having to link with PostGIS at the C level and 
>all it involve in term of release management or to return WKT 
>geometries and thus using PostGIS just at the SQL level, facilitating
supports for former/newer PostGIS versions. An argument against linking with
PostGIS is available at this location:
>
>http://trac.osgeo.org/postgis/wiki/WKTRaster/SpecificationWorking01#Why
>isitimportnattoavoidlinkingwith
>PostGIS
>
>The most cited tool to do such operation right now is StarSpan 
>(http://starspan.projects.atlas.ca.gov)
>
>There is plan to implement a raster/raster intersection function as 
>well but the exact result of such an operation is still to determine.
>
>Thanks for your thoughts.
>
>Pierre
>
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