[postgis-users] Rast index : Could not get raster's convex hull

[Francois Hugues]

Hello,

Here is an error I don't understand when I want to index som tiles from
a raster table :
ERROR:  RASTER_convex_hull: Could not get raster's convex hull

Here is the query which does not work: 
create index slopes_alpes_rast on rasters.slopes_alpes using
gist(st_convexhull(rast));

Here are queries that does work without any error :

1. simple select give me a geometry for all of my tiles and no one is
null:

select rid, st_convexhull(rast) from rasters.slopes_alpes

2. simple select + index on newly created table :

create table rasters.tmp_index_gist as select rid, st_convexhull(rast)
geom from rasters.slopes_alpes
create index tmp_idx on rasters.tmp_index_gist using gist(geom)

It's weird, isn't it ? Any idea of what's happening ? Where do I make a
mistake or what is wrong with my data ?

Hugues.