[postgis-users] ST_Reclass - oposit direction in reclass

[Bborie Park]

On Mon, Dec 12, 2011 at 6:42 AM, Stanislav Vanecek <S.Vanecek at dhi.cz> wrote:
> Hi
>  I am using the ST_Reclass to create 3-band TIFF (for graphical
> presentation) from 1 band grid 32BF (using algorithm described in 32BF
> http://postgis.refractions.net/documentation/manual-svn/RT_ST_Reclass.ht
> ml)
> The problem is, then for the mapping both intervals in (reclassexpr
> text) must be increasing  - values from small to high is mapped to
> colors from "small  to high" = (black to white for example) - and I like
> to have them in opposite order.
> I am working with the big rasters (2000 x 2000 cells). In this case the
> ST_Reclass is already not very fast - and when I try to use map algebra
> it was very, very slow.
> Did someone have idea how to speed up?

Standa,

Can you post your SQL?  I don't think there is anything restricting
you from having your intervals from high to low instead of low to
high, but I could be wrong.  ST_Reclass should be faster than
ST_MapAlgebra as all evaluations are done in C instead of going back
and forth with the PostgreSQL server.

-bborie

-- 
Bborie Park
Programmer
Center for Vectorborne Diseases
UC Davis
530-752-8380
bkpark at ucdavis.edu