[GRASS-dev] [bug #4827] (grass) Building topology for vector is incredibly slow

[Hamish]

> this bug's URL: http://intevation.de/rt/webrt?serial_num=4827
> ---------------------------------------------------------------------
> 
> Subject: Building topology for vector is incredibly slow
> 
> Platform: Mac OSX
> grass binary for platform: Downloaded precompiled Binaries
> GRASS Version: 6.1.cvs_060624
> 
> Raffaele Morelli
> I am working with several vector files from Italy I have imported from
> shape files with v.in.ogr. Those data comes with ISTAT census, so they
> are organized in several small polygons for each town (called
> "sezioni"). I wanted to produce a global national vector with polygons
> representing towns instead small areas inside towns, so I started
> running a shell script with all the "v.extract -d .. .... " to
> dissolve boundaries from the same town. Finally I came into a national
> vector map after patching the regional maps previously obtained
> gatering towns from the same region.
> 
> 
> After this I launched a v.clean to remove duplicates,small angles and
> break poligons. The process runs normally but when it's time to build
> topology at the end of v.clean the process is incredibly slow. After
> 50 minutes is still running and the building areas progress is at
> 33%!!!
> 
> is this 'normal'?


run v.split before v.clean.


grass6/doc/vector/TODO says:

v.in.ogr
--------
It would be useful to split long boundaries to smaller
pieces. Otherwise cleaning process can become very slow because
bounding box of long boundaries can overlap large part of the map (for
example outline around all areas) and cleaning process is checking
intersection with all boundaries falling in the bounding box.


Hamish