[GRASS-dev] v.what.rast speedup

[Markus Neteler]

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:

g.region rast=elevation.10m
r.random elevation.10m vect=elevpnts n=5000 --o
v.db.addcol elevpnts col="height double precision"

# old
time v.what.rast elevpnts rast=elevation.10m col=height
real    0m25.253s
user    0m24.756s
sys     0m0.308s

# new
real    0m24.040s
user    0m23.707s
sys     0m0.297s

Interestingly, timing rather identical (also for 1000). Using the DBF 
driver here.

Markus
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