[GRASS-dev] [bug #4452] (grass) r.patch makes mosaics slowly

[Hamish]

> this bug's URL: http://intevation.de/rt/webrt?serial_num=4452
> ---------------------------------------------------------------------
> 
> Subject: r.patch makes mosaics slowly
> 
> r.patch currently takes current_region_rows * current_region_columns *
> number_of_input_maps time to compile mosaics. It has some reasonable
> optimizations for patching an existing large map with many small
> patches, but is quite unsuited to mosaics.
> 
> For mosaics the fast thing to do would be to iterate over input maps
> (bounds of input, resolution of current region), copying values to
> nulls in the output. (and non-zero values to zeros or nulls in the
> output with the -z switch).


isn't this just the r.mapcalc solution?

Eric wrote:
> r.mapcalc "$OUTPUT=if(isnull(Map_A), Map_B, Map_A)"


hint:

g.region rast=map1,map2,map3,map4

extends the region to enclose all listed maps. Helpful for r.patch.


I think in the end you will spend lots of time for little gain on this
problem- no matter how you frame it, you still have to read each cell of
each map. Just set the thing to run from a script before you leave for
the day & the result will wait for you in the morning. (unless you have
10,000 maps to patch or want real time availablility)


Hamish