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3

Something that is hopefully pretty easy.

I would like to be able to swap the direction of a polyline/line in QGIS. I made a custom tool to do this in MapInfo a couple of years ago, however I can't seem to find anything for QGIS.

Does anyone know of a tool to do this?

If one doesn't exist then I'm happy to have a go at making it, just didn't want to if one has already been made.

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2  
Would be great to have. I don't know of any such native QGIS function. – underdark♦ May 4 '11 at 6:26
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I have a good idea how I can do this pretty easily, I'll see if I can whip up something tonight. – Nathan W May 4 '11 at 8:51
Great! Maybe it can be added to ftools/vector tool box. – underdark♦ May 4 '11 at 8:53
since you have already got the core taken care of, any chance you want to tackle this question, but for QGIS? gis.stackexchange.com/questions/9286/… resources.arcgis.com/content/kbase?fa=articleShow&d=20961 – RyanDalton May 4 '11 at 23:24
Here is the ticket: hub.qgis.org/issues/4936 – Mike Toews Mar 6 '12 at 20:58

2 Answers

up vote 16 down vote accepted

Ok here is the Python that I used to do it:

layer = qgis.utils.iface.mapCanvas().currentLayer()
for feature in layer.selectedFeatures():
   geom = feature.geometry()
   nodes = geom.asPolyline()
   nodes.reverse() 
   newgeom = QgsGeometry.fromPolyline(nodes)
   layer.changeGeometry(feature.id(),newgeom)

Pretty easy!

I have wrapped it up in a plugin called Swap Line Direction and it's available in the QGIS plugin installer.

I'll have a look at how easy it is to intergrate with fTools.

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so you created your own solution - well done - can it be added to ftools? – Mapperz♦ May 4 '11 at 21:36
I'm sure it can, I'll just have to look at the way fTools is coded and write a patch. – Nathan W May 4 '11 at 22:02
Fantastic! Solutions like this are the reason I like using QGIS. Nice job Nathan - BTW I like your little catalogue type plugin aswell! – Ando May 4 '11 at 22:05
@Ando Thanks! I'm beta testing a few new ideas, just wish I had more time to work on it so I could get it out quicker. – Nathan W May 4 '11 at 22:17
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That is really awesome that you worked up a solution so quickly and elegantly. The power of Open Source wins again! – RyanDalton May 4 '11 at 22:20
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up vote 5 down vote

If you have the GRASS plugin use the v.flip option - http://grass.osgeo.org/wiki/GRASS_AddOns#v.flip

enter image description here

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hmmm was hoping for a more QGIS native way, don't have GRASS install at the moment. But it's a good tip for people that do. – Nathan W May 4 '11 at 5:55
would be good to have in python and add to ftools noted by underdark. – Mapperz♦ May 4 '11 at 13:41

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