[GRASS-user] trace processing time

[Hamish]

Tim Michelsen wrote:
> I am doing a v.overlay on large data sets.
> 
> After the process finshes I would like to something like:
> processing time for command "v.overlay" with parameters "yourparameters"
> was 30min.

It may speed things up a lot to first do a preprocessing step with v.select to
reduce the v.overlay operation to features of interest.

To date v.select only offers operator=overlap*. If you want not_overlap you can
do a trick with v.in.region to make a negative mask.

[*] for a patch see http://thread.gmane.org/gmane.comp.gis.grass.devel/9855/
("operator=discrete"?)


v.extract can be useful too (by feature type, SQL query, ...).
or v.in.ogr spatial= in the first place.


there is also the classic Florida coastline problem, if a single polygon is
huge:
  http://thread.gmane.org/gmane.comp.gis.grass.user/7391/
see also doc/vector/TODO  : 2.) v.in.ogr

"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."


in that case you might try v.split first to break the huge boundary into a
number of connected polylines. (does not affect topology, just internal
storage)


Hamish



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