[GRASS-dev] v.build: why is attaching islands taking so long?

[Maciej Sieczka]

Hamish pisze:
> Maciej Sieczka wrote:

>> Can anybody possibly explain why does the "Attaching islands..." in
>>  v.build take so very long compared to other operations? For
>> example: I have a big vector map consisted only of lines, more than
>>  180 000 of them. v.build on this dataset takes about 20 seconds.
>> After converting lines into boundaries (v.type), v.build on that
>> new vector map made of boundaries only takes half a day, with 99%
>> of processing time dedicated to "Attaching islands...". Is that
>> normal? Any improvements possible?

> the not-thinking-about-it-much guess is to blame the "florida
> coastline" problem. to test is that is the problem, try running
> 'v.split vert=1000' before v.type and see if it still takes a long
> time.

'v.split vert=1000' reduces the processing time from over 10 hours to 10
minutes. Strange world we live in.

> you might try running a subset through a profiling tool if you like: 
> http://grass.osgeo.org/wiki/GRASS_Debugging#Using_a_profiling_tool

If I find time I'll try and post here.

> does the boundary data contain many small slivers?

Yes. It's GSHHS actually.

Thanks for hints Hamish!

Maciek

-- 
Maciej Sieczka
www.sieczka.org