[raster] Support for reading offline band data

[dustymugs]

Add functionality to load offline bands so that the PostGIS raster functions can be used. The data will be read-only instead of read-write due to several issues:

1. filesystem privileges: will the user account that the postgres process have write access to the raster file and containing directory?

2. offline raster format: does the format of the offline raster permit direct modification of a band value or is an intermediary format required?

Once read-only access is complete, the out_db column of raster_columns view will be reintroduced. In the new iteration of the out_db column, it will be an array of booleans where each element indicates that the band's data is offline.

[dustymugs]

Added support in r8730. Next is to restore the out_db column to raster_columns.

[dustymugs]

Added out_db column to raster_columns in r8733. All that is left is whether to provide write support.

[pracine]

We are then near to full support for out-db raster right?

I guess one thing missing is raster2pgsql to create filesystem tiles (and overviews) in a new folder when using the -t option in conjonction with the -R option. That would require to specify a new path where to store the tiles though. We could also just prohibit using both options at the same time and take for granted that users are registering already made tiles (using GDAL for example)...

We also need a way to convert out-db rasters to in-db rasters. This is the ST_MakeBandInDB(rast, band) function of Objective FV.18.

[dustymugs]

Replying to pracine:

We are then near to full support for out-db raster right?

Yes. Out-db rasters are supported for analysis. Out-db rasters have no write support so you cannot use ST_SetValue or anything like that.

I guess one thing missing is raster2pgsql to create filesystem tiles (and overviews) in a new folder when using the -t option in conjonction with the -R option. That would require to specify a new path where to store the tiles though. We could also just prohibit using both options at the same time and take for granted that users are registering already made tiles (using GDAL for example)...

It would be nice to have out-of-db overviews supported. Some work will need to be done to see how best to hook the overview into PostGIS Raster.

We also need a way to convert out-db rasters to in-db rasters. This is the ST_MakeBandInDB(rast, band) function of Objective FV.18.

Yes. This is a missing feature. For 2.1 in my opinion.