[GRASS-dev] v.what.rast speedup
neteler at fbk.eu
Sun Oct 21 18:04:22 EDT 2007
Glynn Clements wrote:
> Markus Neteler wrote:
>> >> > since v.what.rast is (for me) extremely slow, I have added
>> >> > cover map support to r.random.
>> >> ..
>> >> > PS: v.what.rast still running on just 300k points while I
>> >> > implemented above :-) Anyone who could make v.what.rast faster?
>> >> Maybe it's the qsort(), maybe it's the i,j loop within a loop.
>> > The loop is certainly inefficient. Rather than shifting the entire
>> > array down every time it finds a duplicate, it should keep separate
>> > source and destination indices, e.g. (untested):
>> > for (i = j = 0; j < point_cnt; j++)
>> > if (cache[i].cat != cache[j].cat)
>> > cache[++i] = cache[j];
>> > else
>> > cache[i].count++;
>> > point_cnt = i + 1;
>> I am afraid to say that I don't know how to implement the suggestion
>> in v.what.rast...
> --- vector/v.what.rast/main.c 17 Oct 2007 14:07:23 -0000 1.26
> +++ vector/v.what.rast/main.c 21 Oct 2007 17:52:42 -0000
> ... patch
Thanks (for your patience): I have made a Spearfish test:
r.random elevation.10m vect=elevpnts n=5000 --o
v.db.addcol elevpnts col="height double precision"
time v.what.rast elevpnts rast=elevation.10m col=height
Interestingly, timing rather identical (also for 1000). Using the DBF
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