[GRASS5] Compression (?) of CELL maps (int)

[Bernhard Reiter]

On Thu, Jun 05, 2003 at 10:20:58PM +0100, Glynn Clements wrote:
> Markus Neteler wrote:
> 
> > Question: Are CELL maps compressed?
> 
> G_open_cell_new() and G_open_raster_new(..., CELL_TYPE) create a
> compressed map; but ...
> 
> > If yes, the compression
> > rate seems to me much lower than for FCELL.
> 
> FCELL/DCELL data is zlib (gzip) compressed; CELL is RLE-compressed,
> which is much less effective.
> 
> > GRASS:/ssi-data/grass/PERMANENT/cell > l
> > -rw-r--r-- 1 grass fepssi 78518805 Jun  5 15:42 060150.g.s9_SA_135.int
> > 
> > GRASS:/ssi-data/grass/PERMANENT/cell > gzip 060150.g.s9_SA_135.int
> > 
> > GRASS:/ssi-data/grass/PERMANENT/cell > l
> > -rw-r--r-- 1 grass fepssi 49847399 Jun  5 15:42 060150.g.s9_SA_135.int.gz
> > 
> > -> 63 %
> > 
> > Can we somehow improve the situation?
> 
> Use zlib for CELL maps. But that means messing with the core raster
> I/O functions.
> 
> FWIW, I intend to completely re-write the raster I/O code once I move
> to 5.1. 

Wouldn't be better to wait for 5.3 for this then?

> The existing code isn't particularly legible; two significant
> bugs which were introduced with the addition of FP and NULL support
> managed to remain undetected until after 5.0.0 was released.

Is there a possibility to only fix the bugs first?

> Also, there appear to be significant performance issues with that
> code; the limiting factor ought to be the raw disk I/O rate, but that
> doesn't appear to be the case at present.
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