[GRASS-dev] r.clump4p - OpenMP version of r.clump

[Moritz Lennert]

On 23/02/14 23:10, Markus Metz wrote:
> There is an OpenMP version of r.clump available at
>
> http://sil.uc.edu/downloads.html#software
>
> called r.clump4p. The reported performance gain is 450 times over the
> original r.clump.
>
> The performance gain over the original r.clump vanished:
> r.clump4p with one thread is now about 12x slower than r.clump, and
> r.clump4p with 4 threads is now about 5x slower than r.clump.
> Moreover, the results of r.clump4p are wrong, it clumps together areas
> with different cell values (no multithreading effect).
>
> I tested in a region with 650 million cells, both modules produced
> about 17.6 million clumps. All differences in the resultant clumps
> were due to errors in r.clump4p.
>
> Tests were performed in GRASS 7 where I have optimized r.clump and
> also added support for diagonal clump tracing.

Great work ! Thanks a lot, Markus !

Moritz