Lost's of thanks for your reply, this will help me one step forward.
Well, then let's get lost... 
Andrea
On Tuesday 30 March 2004 22:17, Glynn Clements wrote:
Andrea Antonello wrote:
> I need to understand how GRASS reads and writes the raster data from
> disk. The developer Manual doesn't go much into detail and I'm having big
> problems to get lost inside the code...
No surprise there. I probably understand that code as well as any of
the current developers, and I also get lost inside the code.
FWIW, the relevant files are opencell.c, get_row.c, put_row.c and
closecell.c, all in src/libes/gis.
> Any hint on used algorithms (LZW?)
LZW was used at one point, but isn't supported in 5.x. Integer maps
are stored in big-endian order using a sign bit (*not* twos
complement), with optional run-length compression; floating-point maps
are encoded using XDR and optional zlib (gzip) compression.
The core functions for writing are put_data/put_fp_data. For reading,
there aren't really any core functions; the process seems to be evenly
distributed across most of get_row.c.
> or documentation parts I missed are appreciated.
AFAIK, the only viable source of information on the raster map formats
is the source code.
> PS: is there some project ongoing that aims to rewrite the raster I/O
> libs in any programming language?
I'll probably do it one day, unless someone else gets there first.
--
____________________________________________________________________________
University of Trento
Department of Civil and Environmental Engineering
Via Mesiano, 77 - Trento (ITALY)
Andrea Antonello
tel: +393288497722
fax: +390461882672
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