Hi Andy, The qgis-community-team list is rather about QGIS website and documentation management.
To get help on QGIS tools, better write to qgis-user@lists.osgeo.org (I'm ccing your message) More information about lists at http://qgis.org/en/site/getinvolved/mailinglists.html Regards 2016-02-09 16:51 GMT+01:00 Andy Gillett <andy.gill...@lqm.co.uk>: > Dear List > > > > I have just started using QGIS for some spatial processing work (using > Dissolve & Buffer) and encountering some problems with run-time and > hanging. Probably down to my relative inexperience! So would be very > grateful for some feedback or suggestions. I have spent a fair bit of time > searching various information sites such as GIS Stack Exchange but with no > luck yet. > > > > *Objective* > > I am trying to Dissolve approx. 500,000 polygons which represent a 250m > buffer around many line segments (e.g. electrical cable network or could be > a road network). I have 5 buffer distances to create in total. The 500,000 > polygon shp file is a sub-set (approx. 1/10th) of the entire dataset > requiring processing in this way. > > > > *Issues / Questions* > > Have tried to use the Dissolve (polygon) on the 250m Buffer polygon > dataset or Dissolve (line) function on the line network dataset in QGIS but > it’s very slow or doesn’t work on the above (unrealistic run-time … > overnight still running). > > Is there a limit on the number of polygons or lines that QGIS can handle > for some of the operations (Dissolve, Buffer, etc)? > > Is the desktop QGIS Dissolve function just plain slow? > > Do I just keep reducing the polygon sub-set dataset size until I find a > workable solution? > > Would the ArcGIS Dissolve function be quicker/handle the 500,000 polygon > dataset above? > > > > Looking on GIS Stack Exchange I came across SAGA and have successfully > used the Dissolve (line) function (lightening quick) – thinking I could > then Buffer to 250m, etc in QGIS or in SAGA – but for both (QGIS & SAGA) of > those options leaves the operation just crawling along very slowly or just > not working, it is hard to tell. > > > > The Dissolve (polygon) function on the 250m Buffer dataset in SAGA appears > to work initially very fast and gets to circa 80+% on the activity bar and > then just stops and appears to go nowhere (i.e. runs out of memory I > suppose). Another search on e-bulletin board suggested there may be a > problem with the Dissolve (polygon) function in the current version of SAGA > v.2.1.2? > > > > I have had a quick look at GRASS but I am not really sure what I am doing > (i.e. not such an intuitive user interface) and wonder if the non-working > function(s)/issues in SAGA would also apply? > > > > > > > > Andy Gillett > > [image: Follow us on Twitter] <https://twitter.com/data4sustain> [image: > Follow us on LinkedIn] <http://uk.linkedin.com/pub/andy-gillett/a/761/650> > > *LQM* > Sir Colin Campbell Building | University of Nottingham Innovation Park | > Triumph Road | Nottingham | NG7 2TU > Tel: +44 (0)115 7484081 | www.lqm.co.uk | *andy.gill...@lqm.co.uk > <andy.gill...@lqm.co.uk>* > > *DATA4SUSTAIN:* Click *here* <http://eepurl.com/bsgFEX> to join our > Data4Sustain mailing list | Click *here* > <http://www.lqm.co.uk/latest/2015/07/data4sustain-feasibility-decision-support-tool-for-renewable-energy-technologies/> > to find out more about the project > > *This email and its attachments may be confidential and are intended > solely for the use of the individual to whom it is addressed. If you are > not the intended recipient of this email and its attachments, you must take > no action based upon them, nor must you copy or show them to anyone. Please > contact the sender if you believe you have received this email in error. > Any views or opinions expressed are solely those of the author and do not > necessarily represent those of Land Quality Management Ltd. No employee or > agent is authorised to enter into any contractual agreement with another > party by e-mail. The recipient should check this email and any attachments > for the presence of viruses. Land Quality Management Ltd accepts no > liability for any damage caused by any virus transmitted by this email.* > > > > > > > > _______________________________________________ > Qgis-community-team mailing list for organizing community resources such > as documentation, translation etc.. > qgis-community-t...@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/qgis-community-team >
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