[postgis-users] RE: PostGIS WKT Raster

Pierre Racine Pierre.Racine at sbf.ulaval.ca
Thu Jul 10 10:31:38 PDT 2008

Thanks for your comments Regina, 

>if you look at Dane's posed problem in
>previous postgis post, it is a common scenario where I have really
>wanted RASTER in the database and where your proposed
>ST_Intersection(RASTER, VECTOR), ST_Interects(RASTER,VECTOR) would have
>worked nicely (e.g. steps from his problem)
>3) perform an elevation lookup to raster data to calculate the gradient
>of each 500 ft segment

He could effectively get the elevation at each end points doing
ST_Intersection(RASTER, VECTOR, "VECTOR") and then compute the gradient
between the two resulting vectorial point values...

>It may be also interesting to look at what Manifold.net handles RASTERs
>since they have an SQL implementation that considers RASTERs. Granted
>they are not closed source. 

There seems to be a very interesting set of raster/vector functions. We
could also have chosen to work with ArcObject. However we have decided
to go OpenSource (even if Manifold is very cheep). We also need a VERY
stable base and ArcGIS has proven to fail on many of the same kind of
operation we need while PostGIS could do them perfectly (in many hours

>I think when most people think of RASTER they think aerials 
>(well that's
>what I think of) mostly because all the people I know using ArcSDE and
>Oracle RASTER use it for just that and pretty much nothing else.
>Granted you can do analytically useful stuff with it such as extrude
>building footprints from the aerial, but people seem content to do that
>kind of stuff with non-db tools or just assume its some magic 
>offered by mystical gods working up there.

Right. The problem arise when you want to develop web applications...
Personnally, I work with scientists used to do analysis with GISs. And
now we want some of these operations on the web so people do not have to
struggle with dataset preparation, learning ArcGIS and waiting hours for
the result. So going with PostGIS seemed natural to me. We'll have
someone feeding the system with base datasets (many layers of Canada
variables), we'll make the operations as simple to do as they can be,
and we'll put that on a VERY powerful server. I could write code to do
the analysis we need outside of the database, but this would still be
reinventing the wheel. So I chose to implement it directly in the
database hoping this will help people solving other problems as well.


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