[postgis-users] ST_Mapalgebraexpr requires same alignment
Jose Carlos Martinez
jomarlla at cgf.upv.es
Thu Mar 22 10:00:58 PDT 2012
Hi. Im trying to use mapalgebra between two layers with tiles, I get
NOTICE: The two rasters provided do not have the same alignment.
The resulted tiles are empty. Does ST_Mapalgebraexpr require same
alignment? According to the docs I guess not but then dont know why im
getting that message.
In another example I didnt use st_union with the same result.
insert into demdif (rast) select st_mapalgebraexpr (d1.rast, 1, st_union
(d2.rast), 1, 'abs([rast1.val] - [rast2-val])','16BSI', 'FIRST', null,
null,null) from dem200 d1, dem d2 where d1.rast && d2.rast and st_relate
(d1.rast::geometry, d2.rast::geometry, 'T********') group by d1.rid;
Another issue is st_union (internally is st_mapalgebraexpr) is extremely
slow. I can not manage raster layers bigger than a couple of thousand
pixel in x or y even with 128 tiled blocks.
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