[postgis-users] Creating a multiband raster from 3 single band rasters

[Mark Wynter]

I'm hoping someone can suggest a way of efficiently combining 3 individual (but concordant) single band rasters into single raster having 3 bands?  We're working with PostgreSQL9.1, PostGIS2.1Beta.

The starting point is a single tiled raster with 3 bands representing RGB values.

Let's say we perform some color smoothing on each of the RGB bands using mapalgebra.

CREATE TABLE resample_myrastertable_b1 AS
SELECT rid, st_mapalgebrafctngb(rast, 1, '8BUI', 5, 5, 'st_mean4ma(float[][],text,text[])'::regprocedure, 'ignore', NULL) as rast FROM original_rastertable;

CREATE TABLE resample_myrastertable_b2 AS
SELECT rid, st_mapalgebrafctngb(rast, 2, '8BUI', 5, 5, 'st_mean4ma(float[][],text,text[])'::regprocedure, 'ignore', NULL) as rast FROM original_rastertable;

CREATE TABLE resample_myrastertable_b3 AS
SELECT rid, st_mapalgebrafctngb(rast, 3, '8BUI', 5, 5, 'st_mean4ma(float[][],text,text[])'::regprocedure, 'ignore', NULL) as rast FROM original_rastertable;

This gives us 3 single-band results rasters. 

How do we now join the individual smoothed RGB "results" rasters into a single multiband "results" raster?   We'd also like to add a 4th band to the "results" raster based on say a calculation which references the smoothed values in bands 1-3.

I'm getting reasonably comfortable writing MapAlgebra callback expressions.   Its more a case of how do we efficiently handle table operations (e.g. appending single band raster outputs) each time we perform some MapAlgebra?  

Any suggestions and or a simple worked example would be most appreciated.

Many thanks

Mark