I'm doing my internship in a consulting office which is switching from MapInfo to QGIS/GRASS 1.8.0.
I posted here a few days ago about the way to clean a polyline from a Lidar data with v.clean.
I've tried all algorithms possible, made every test I could try, without obtaining a cleaned polyline without any topological error.
Now I'm working on many other projects, and I realize that most of data coming from MapInfo or ArcGIS users are full of topological errors for QGIS/GRASS.
I'm feeling fear growing up, because I still didn't find the way to clean all those data with QGIS/GRASS. And I've tried all I could.
I used break then rmdangle to erase dangles with a good threshold, but it didn't work every time. I tried rmarea to erase some little islands of lines but it don't work if you want to keep the main polyline, I tried snap to full the holes in the line but it creates more artefacts if the threshold is too high, and it don't snap if the threshold is too small.
I think that it is obviously a big question that anyone working with QGIS/GRASS in a professionnal environment must face. But on the other hand I'm very surprised to see that many people like me asking help for this problem finally never find answers. Is it a taboo subject ? Or is it so simple to use v.clean that there's no comment to do ?
So I'm adressing those who often need at work to clean their layers with a hundred errors of all kind (double geometry, dangles, self-intersection...).
How do you success at cleaning it until you have 0 errors ?
Usually, people says "v.clean is powerful, you just need to launch rmdangle for dangles...". I just give you a quote from GRASS documentation : " Topological errors can be corrected either manually within v.digit or, to some extent, automatically in v.clean."
What is "some extent" ? From my small experience, it seems not to be a very large extent...and if this extent is very small, do you correct all the other errors manually ? Is there more option than v.clean to correct topology ?
I promise that if I find the answer, i'll post a very complete tutorial for beginners and idiots like me.
Thank you very much for your help, I think we are numerous to struggle with topology !!