[postgis-devel] Raster todo list

[dustymugs]

>
> What I understand up to now, to make a correspondance between the vector version and the raster version of ST_Accum, ST_Collect and ST_Union:
>
> -ST_Accum() would create an array of raster (I don't see any use for that up to now).

I have no idea what this is useful besides consuming memory.  Besides, 
isn't this no more than...

SELECT observation_date, array_agg(rast) FROM mytable GROUP BY 
observation_date;

> -ST_Collect() would roughly merge rasters together (last pixel value or first only in the case of overlap so no way to blend pixel values together)

This is exactly what I'm looking for.  Basically, a method to bring back 
together tiles created using raster2pgsql.py

> -ST_Union() would be the most sophisticated (but slower than ST_collect) way of merging rasters together. It could use a set of initial raster, state raster and final raster expressions to determine the final value of the resulting raster pixels. Predefined options could be FIRST, LAST, MAX, MIN, MEAN, SUM, RANGE, COUNT...
>

This would be an advancement of ST_Collect to provide greater control of 
what happens when two pixels overlap.

I also think that ST_Collect and ST_Union need to auto-rectify input 
rasters as it is creating one "collected" raster.

-bborie