[GRASS-user] null files under cell_misc

[Glynn Clements]

Milton Cezar Ribeiro wrote:

> I would like to know if the "null" files, under
> $my_mapset/PERMANENT/cell_misc/(my_raster_map),
> is a usefull file, our if I can delete it. The HD space used for each of my
> mapsets are quite large (~20GB).

Those files record which cells are null.

If you delete the cell_misc/<map>/null file:

For an integer map, any cells which were null will become zero, but
any zeroes (cells which were previously either null or zero) will be
treated as nulls (this is for compatibility with GRASS 4.x, which
didn't have a null file, but typically used zero to indicate a null
value).

For a floating-point map, any cells which were null will become zero
(when writing FP data, a null has a zero written to the fcell/<map>
file, and the corresponding bit is set in the cell_misc/<map>/null
file).

IOW, you can't safely delete the null file unless the map doesn't
contain any nulls and, if it's an integer map, doesn't contain any
zeroes either.

-- 
Glynn Clements <glynn at gclements.plus.com>