[GRASS-dev] Rast_open_update?

[Sören Gebbert]

Hi Huidae,
FWIK, the reason why updating raster maps is currently not supported
in GRASS at the module level is the storage format. Usually raster
maps are stored using zip compressed rows. Rows are written in serial,
hence if you modify a single row, the size of this row may be
different after compression and does not fit exactly in the position
of the old row in the existing file. From my knowledge there is
currently no way to append rows or mark rows as invalid in existing
raster maps.
However, there is the possibility to store raster maps using
uncompressed rows, but i don't recall any raster library function to
update such maps.

Best regards
Soeren

2014-06-26 15:05 GMT+02:00 Huidae Cho <grass4u at gmail.com>:
> Whenever I change a couple of cells in an existing raster map, I have to
> create a new raster map and patch the old and new maps, which can take long
> because r.patch has to read and write the entire map.
>
> There are Rast_open_old/new, but no Rast_open_update and AFAIK there are no
> raster modules that directly update existing raster maps. I don't know why.
> I thought it would be great if there was Rast_open_update so we can update
> existing raster maps without creating a temp map and patching it.
>
>
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