[postgis-users] PostGIS Raster efficient enough to get height given coords from a large DEM?

[Paragon Corporation]

> Yes, you are correct about the significant performance issues 
> with calling ST_SetValue for each pixel of a raster.  This 
> unfortunately has to do with the deserialization and 
> serialization that occurs every time ST_SetValue is called.
> 
> Hopefully, I can get to it before the 2.0 code freeze but the 
> outlook doesn't look good.
> 
> -bborie
> 
> --

Not sure it helps but as a work-around I define my values I want to set as 
a multipoint collection (Basically SELECt ST_Collect(my_grid_points), val
FROM myresults GROUP BY val

which I then convert to ST_AsRaster and then use ST_MapAlgebra to burn
into my main raster (one for each grouping using a union call)

http://www.postgis.org/documentation/manual-svn/RT_ST_AsRaster.html

http://www.postgis.org/documentation/manual-svn/RT_ST_MapAlgebraFct2.html


That I think works pretty fast (well much faster than ST_SetValue anyway).
I haven't bothered demonstrating the technique 
since it will quickly become obsolete with the ST_Union already in place
(not yet documented) (though which needs some cleanup)
and also the other functions Bborie/Pierre have discussed/planned.

Thanks,
Regina
http://www.postgis.us