[GRASSLIST:5824] Re: r.mapcalc and data compression

[Glynn Clements]

Jan Bartholdy wrote:

> I am using Wingrass generic in a cygwin environment/windows xp. After a
> simple processing of raster maps with r.mathcalc, the resulting maps are
> about 17times larger (from about 28 to about 510 MB in the fcell
> subdirectory of the mapset) than the original maps (the original data
> are 2800, 2900 etc.; the resulting data are 25.5, 29.8 etc). Does a
> possibility to compress the resulting data? Thanks, Jan Bartholdy

There are several possible reasons for expansion, including:

a) the result was generated at a higher resolution than the input maps.
b) the input maps are compressed but the output maps aren't.
c) the input maps are 1- or 2-byte integer maps but the output maps
are 4- or 8-byte floating-point.

For a), set a lower resolution with e.g. "g.region res=...".
For b), use r.compress.
For c), explicitly coercing the data with int(...) will use 4-byte
integers; AFAICT, there isn't any way to convert a map to 1- or 2-byte
integers.

-- 
Glynn Clements <glynn.clements at virgin.net>