[postgis-users] ST_Mapalgebra

[Bborie Park]

Joan (and anyone else using 2-raster MapAlgebra),

You don't need to specify ::double precision in your expressions.
Under the hood, your expression is wrapped with parentheses and
::double precision.  So, if your expression was

CASE WHEN rast2 > rast1 THEN rast1 ELSE rast2 END

Internally, the expression becomes

SELECT (CASE WHEN rast2 > rast1 THEN rast1 ELSE rast2 END)::double precision

-bborie

On Tue, Nov 22, 2011 at 6:51 AM, Joan <wamaithajoan at gmail.com> wrote:
> I have tried it and it works. Thank you Pierre.
>
> On 22 November 2011 15:33, Pierre Racine <Pierre.Racine at sbf.ulaval.ca>
> wrote:
>>
>> > I have used ST_MapAlgebraExpr but I get the error below.
>> >
>> >
>> > select * from (select ST_MapAlgebraExpr(kb.rast, kb1.rast,
>> > 'kb1.rast+kb.rast') as
>> > rast from kb_dsm_clip kb, kb_dsm_clip100 kb1) as r1 limit 5;
>> > ERROR: missing FROM-clause entry for table "kb1"
>> > LINE 1: SELECT (KB1.RAST+KB.RAST)::double precision ^
>> > QUERY: SELECT (KB1.RAST+KB.RAST)::double precision
>>
>> Try this instead:
>>
>> SELECT ST_MapAlgebraExpr(kb.rast, kb1.rast, 'rast1 + rast2') as rast
>> FROM kb_dsm_clip kb, kb_dsm_clip100 kb1
>> WHERE st_intersects(kb.rast, kb1.rast)
>>
>> 1) There is no need for a subquery
>>
>> 2) You must refer to the raster using 'rast1' and 'rast2', not their real
>> names
>>
>> 3) I don't know if your rasters are tiled but it is always a good idea to
>> restrict the process to intersecting footprints.
>>
>> Pierre
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>
>
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-- 
Bborie Park
Programmer
Center for Vectorborne Diseases
UC Davis
530-752-8380
bkpark at ucdavis.edu