[GRASS-user] v.lidar.edgedetection very slow

Michael Perdue michael_perdue at yahoo.ca
Mon Jun 22 01:00:35 EDT 2009

On 19-Jun-09, at 8:54 PM, Hamish wrote:

> Michael wrote:
>> I actually get the same thing.
>> For the first while the process runs in full use
>> of one core, but once the process starts writing results to
>> the db, the whole process bogs down to a
>> grinding halt. CPU usage for v.lidar.edgedetection
>> drops down to ~1% (1% of one core) and sqlite usage rises to
>> ~16%. Maybe I'm wrong, but my impression was that the
>> bottle neck was the modifications to the database.
> hmmm. I've seen no problems on Linux64 + DBF backend. 100% core until
> completion.
> Are you running WinXP + SQlite? Can you try with the DBF driver?
> maybe the common problem is in the SQLite driver...  ??

I'm running Mac OS X + SQLite with a 64 bit version of grass. I ran a  
whole bunch of tests today and it looks like there are at least a  
couple of things going on and SQLite is one of the issues. I ran a  
500m x500m tile with three different DB back-ends (SQLite, Postgres  
and DBF) and these are the results I obtained;
time v.lidar.edgedetection input=Cal_QTile output=Cal_QTile_edges
real	38m53.458s
user	1m17.602s
sys	4m6.353s

time v.lidar.edgedetection input=Cal_QTile output=Cal_QTile_edges
real	6m49.060s
user	0m46.622s
sys	1m20.324s

time v.lidar.edgedetection input=Cal_QTile output=Cal_QTile_edges
real	1m54.065s
user	0m48.530s
sys	1m8.686s

The results with Postgres and SQLite were a real surprise to me.
> if you build from the latest grass 6.5 or 7 svn you can use the -- 
> verbose
> flag to follow the action. setting 'g.gisenv set="DEBUG=1" gives you
> even more detail (even with existing versions).

Does this print out the debugging messages that are in the code or do  
I need to do something else to see those?

> please create your patches with "svn diff > somepatch.diff" and file  
> them
> in the trac system. Otherwise they quickly get lost and forgotten.
> http://grass.osgeo.org/bugtracking/
> https://trac.osgeo.org/grass/wiki/WikiStart#BugTracking

OK, thanks. I'll post a bug report and submit a patch soon.



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