Hi Soeren, Ah! You're right.
Cell files have pointers to rows in the header, so maybe, we could implement functions that can copy multiple rows at a time without uncompressing/compressing them row by row even if MASK may not be applied properly. This is not a true update, but at least copy can be more efficient than now. Regards, Huidae On Thu, Jun 26, 2014 at 9:30 AM, Sören Gebbert <[email protected] > wrote: > 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 <[email protected]>: > > 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. > > > > > > _______________________________________________ > > grass-dev mailing list > > [email protected] > > http://lists.osgeo.org/mailman/listinfo/grass-dev >
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