[Qgis-user] Clipping tool takes a lot of time

[Filipe Dias]

Yes, convert format is based on ogr2ogr but I dont think it can be modified
to do "clip". Why don't you try running ogr2ogr from the command line?

You need to navigate to the directory where both your shapefiles are stored
and run the code just like in the blog post. I tried on Linux but it should
be the same on Windows (command line on Windows is "command prompt").

ogr2ogr -clipsrc clipping_polygon.shp output.shp input.shp

Hope it helps

PS: It would be nice to add a "clip" algorithm based on ogr2og with -clipsrc
since it seems to be much faster

On Thu, Oct 16, 2014 at 1:16 AM, Jonas Sjögren <jonas.sjo at gmail.com> wrote:

> Hi again,
> unfortunately the processing is quite slow again with the difference
> algorithm, about 2,5 hours. With a script running with 60 iterations the
> total processing time will be about a week. No other processes are running
> except for internet. The script sequence is
> processing.runalg( 'qgis:difference', InputRoadNetwork, ClippingPolygon,
> OutputRoadNetwork )
> I have tried the 'gdalogr:ogr2ogr' clipping algorithm expressed in
> http://darrencope.com/2011/03/31/clipping-large-shapefiles-using-ogr/ and
> http://www.gdal.org/ogr2ogr.html
> which I believe corresponds to the algorithm GDAL/OGR [32 geoalgorithms]
> => [OGR] Conversion => Convert format in the Processing Toolbox. Still I
> do not know how to get the code right in 'Creation Options'. It should be
> something like
> [-clipsrc ClippingPolygon.shp]. Anyone who has an idea?
>
> Best regards,
> Jonas
>
>
> 2014-10-14 20:36 GMT+02:00 Jonas Sjögren <jonas.sjo at gmail.com>:
>
>> Hi,
>> to check that my data was ok I tried a clip tool in ArcMap where the same
>> calcuation took exactly 10 seconds. After some modifications in my script
>> and using the 'qgis:difference' algorithm, processing time was reduced to
>> about 5 minutes, quite acceptable. Thank you for helping me sort this out.
>> /Jonas
>>
>> 2014-10-14 7:47 GMT+02:00 Bernhard Ströbl <bernhard.stroebl at jena.de>:
>>
>>> Hm,
>>>
>>> goes pretty fast here, both with PostGIS and shp layers (some 5 lines, 1
>>> polygon, both layers in the same CRS as the project, shp on local drive)
>>> QGIS 2.4 64 bit on Win7
>>>
>>> Bernhard
>>>
>>> Am 14.10.2014 02:49, schrieb Mike Flannigan:
>>>
>>>
>>>> I am also using QGIS 2.4 64b Chugiak on Windows 7.
>>>> The same thing happens to me.  Even when I create
>>>> a line layer with only 11 lines and try to clip 3
>>>> of them with a polygon layer, the progress bar just
>>>> goes back and forth for ever.
>>>>
>>>> I didn't run it for hours to see what would eventually
>>>> happen.
>>>>
>>>> Mike
>>>>
>>>>
>>>> I might be doing something wrong.
>>>>
>>>> On 10/13/2014 8:02 AM, qgis-user-request at lists.osgeo.org wrote:
>>>>
>>>>> Hi,
>>>>> I am trying to clip a road network by a polygon in a script using the
>>>>> algorithm 'qgis:clip'. The result seems to be quite ok but it takes an
>>>>> incredible long time to produce, about 14 hours (!). The road network
>>>>> shapefile consists of about 5000 features (not very many, I believe)
>>>>> and
>>>>> the clipping shapefile consists of one single polygon. When using
>>>>> Vector =>
>>>>> Geoprocessing Tools => Clip from the QGIS menu, the time required is
>>>>> about
>>>>> the same. Does anyone have a clue why it takes so long time? Are there
>>>>> other clip tools that I may try? I?ve been looking at the
>>>>> 'gdalogr:ogr2ogr'
>>>>> algorithm and its clipsrc function but not got it to work properly
>>>>> yet. I?m
>>>>> using QGIS 2.4 Chugiak on Windows 7 with 2.5 GHz processor. Thankful
>>>>> for
>>>>> all hints that may help,
>>>>> /Jonas
>>>>>
>>>>
>>>>
>>>
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