On Mon, 25 May 2009, Even Rouault wrote:
(Sorry, I'm not subscribed to the GRASS-stats list, so I've emailed directly
to the people having taken part to the discussion)
Hi Even,
Thanks for tackling the 2D/3D issue in the GRASS read driver - the fixes
look appropriate.
The SQLite issue is, I believe, on the GRASS side - GRASS can use a number
of databases for storing attribute data, but geometries are stored
natively. This means that GRASS is using its own SQLite handling, I think
shown in OGRGRASSLayer::SetAttributes() in the file you've seen in the
2D/3D fix for determining their types, and in OGRGRASSLayer::GetFeature()
for copying them from GRASS structures to OGR structures. I think that the
OGR driver is limited by GRASS's own driver, but since I don't use SQLite,
I cannot reproduce the problem.
I'll add grass-stats to the CC for completeness.
Roger
About the OGR sqlite performance, I've not read all the posts of the thread,
but I couldn't reproduce any performance related problem.
Here's a simple OGR python script that creates a 1000 row x 1000 column sqlite
db :
#!/usr/bin/python
import ogr
ds = ogr.GetDriverByName('SQLite').CreateDataSource('testhuge.db')
lyr = ds.CreateLayer('test')
for i in range(1000):
ds.ExecuteSQL("ALTER TABLE test ADD COLUMN att%d VARCHAR" % i)
ds = None
ds = ogr.Open('testhuge.db', update = 1)
lyr = ds.GetLayerByName('test')
for i in range(1000):
feat = ogr.Feature(lyr.GetLayerDefn())
for j in range(1000):
feat.SetField(j, 'val%d' % j)
lyr.CreateFeature(feat)
ds = None
(takes a few seconds to run)
Then "time ogrinfo -ro -al -q testhuge.db > /dev/null"
--> real 0m3.903s
So 4 seconds, not 30 minutes... Maybe it's due to the fact how GRASS uses the
OGR output ?
Actually, by reviewing the code, there might *maybe* a performance problem if
the FID or geometry columns of the table were at the end of the column list
(see lines 308-313 and 339-344 in ogr/ogrsf_frmts/sqlite/ogrsqlitelayer.cpp,
latest GDAL SVN head trunk), that could cause loop over each column name
before finding them. But I couldn't really evaluate the impact it could have.
(by default OGR creates these fields as the first ones)
Even
--
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: [email protected]
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