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QGIS is a free, open source, cross platform (lin/win/mac) geographical information system (GIS)
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Vector Fixed Distance Buffer #25976

Closed qgib closed 6 years ago

qgib commented 6 years ago

Author Name: Douglas Alderman (Douglas Alderman) Original Redmine Issue: 18080 Affected QGIS version: 2.18.14 Redmine category:vectors Assignee: Alessandro Pasotti

I opened a arcGIS GDB layer, saved it as a shapefile layer, then edited and kept only the shapes I needed for the region I was working in. I buffered the edited shapefile by using 'fixed distance buffer' in the Vector dropdown menu. The buffering process buffered all but 3 shapes of the edited shapefile. I did this same process on a different GDB in another region and it left some shape(s) unbuffered again. The shapes are there in the edited shapefile.

Related issue(s): #25189 (duplicates) Redmine related issue(s): 17291

qgib commented 6 years ago

Author Name: Giovanni Manghi (@gioman)

qgib commented 6 years ago

Author Name: Douglas Alderman (Douglas Alderman)

Correction, The last 2 sentences of the original description should read as follows: I did this same process with a different layer of the same GDB. This time it also left shapes unbuffered.

qgib commented 6 years ago

Author Name: Douglas Alderman (Douglas Alderman)

The shapefiles I attached are only of a specific region of the original shapefiles I created from two different layers of the same GDB.

qgib commented 6 years ago

Author Name: Alessandro Pasotti (@elpaso)

Can you please check that all the geometries in the input shapefile are valid (do not contain any topological error)? There is a geometry checker function in the vector layers menu.

qgib commented 6 years ago

Author Name: Douglas Alderman (Douglas Alderman)

I so not see the 'geometry checker'. I see 'Densify geometries' or 'simplify geometries' under the 'Vector' dropdown menu at the top. Am I looking in the right place?

qgib commented 6 years ago

Author Name: Giovanni Manghi (@gioman)

Douglas Alderman wrote:

I so not see the 'geometry checker'. I see 'Densify geometries' or 'simplify geometries' under the 'Vector' dropdown menu at the top. Am I looking in the right place?

no, is a core plugin, see if is enabled in the plugin manager.

qgib commented 6 years ago

Author Name: Steve Lowman (Steve Lowman)

I tested both of these features sets in QGIS 2.18.17. They both have invalid geometries, but despite this, the buffer works on both with all features buffered.

Are you sure you did not have all but three features selected? This tool will buffer only the selected features if you have features selected. If you want all features buffered, you must have no features selected.

I think this report can be closed.

qgib commented 6 years ago

Author Name: Alessandro Pasotti (@elpaso)

Closing for now, if you have more evidence, please re-open.

qgib commented 6 years ago

Author Name: Steve Lowman (Steve Lowman)

To be honest, I might unwittingly have been using the SAGA Fixed Distance Buffer instead of the QGIS native algorithm. If so, then I think this report may be a duplicate of #25189, which will not be resolved in QGIS 2.

Best use the SAGA tool, or perhaps even better use the OGR Buffer Vectors tool. Both are available in the Processing Toolbox.

qgib commented 6 years ago

Author Name: Douglas Alderman (Douglas Alderman)

Yes, the SAGA "Fixed Distance Buffer" works. The QGIS "Fixed Distance Buffer" did not work several times for me, leaving out one or more polygons when creating buffers.

qgib commented 6 years ago

Author Name: Douglas Alderman (Douglas Alderman)

I am requesting to reopen this case. Please accept my apologies for my procrastination on the matter.

I have tried the scenario a couple more times myself. I have the same results each time: the QGIS 2.18.14 "Vector" menu, "Geoprocessing Tools", "Fixed distance buffer" is not buffering some of the polygons of the shapefile, but, as suggested by Mr. Lowman, the "Processing" menu, "SAGA", "Vector general tools", "Fixed distance buffer" appears to work very well buffering all of the polygons of the same shapefile. (Please note that I am trying to achieve a 1/4 mile buffer. If the buffer is too large you will not be able to see that the QGIS tool is not working properly.)

Also, I cannot figure out how to use the geometry checker function that was suggested by Mr. Pasotti a while back. Do you know where I can find instructions for using it? I will be glad to try it if I can figure it out.

For now, and for me, the fix is simple and easy...Just use the SAGA tool. However, that does not answer the question of whether or not it was the QGIS tool, the shapefile, or the operator. I hope you will consider reopening the case.

Thanks!!!

qgib commented 6 years ago

Author Name: Steve Lowman (Steve Lowman)

As already stated, I think this is a duplicate of #25189, which was closed with Resolution "wontfix" with the recommendation to use more robust tools in the Processing Toolbox for QGIS 2, while better solutions are developed for implementation in QGIS 3.

Perhaps a better solution for QGIS 2 would be to remove the QGIS tools from the Vector Menu and replace them with the OGR Fixed Distance Buffer and SAGA Variable Distance Buffer algorithms. This would be an easy interim fix for QGIS 2.

In our workplace, we have altered the Menu settings in Processing Options to implement this for all our users already. I recommend these Processing Options settings are changed as a default in the QGIS 2 LTR.

qgib commented 6 years ago

Author Name: Alessandro Pasotti (@elpaso)

qgib commented 6 years ago

Author Name: Alessandro Pasotti (@elpaso)