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I'm looking for a tool that would be able to automatically snap features closer than a given distance. Is there such a tool/plugin for QGIS/GRASS/OpenJump? Would it be possible to achieve that with PostGIS?

I have a river network where some of tributaries don't touch the river they flow in and I need to get them snapped.

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Try v.clean.snap from GRASS QGIS. In PostGIS avaiable ST_SnapToGrid () function – HasT Jan 22 '13 at 12:18
v.clean.snap seems to be doing a great job! Thank you. – Michal Zimmermann Jan 22 '13 at 13:02
If two rivers touch, how do I tell which one is a tributary? I tried with ST_EndPoint(), but obviously some of the tributaries touch the river at the StartPoint as there is no way to tell which point it actually starts at. – Michal Zimmermann Jan 22 '13 at 13:40
up vote 1 down vote accepted

In GRASS GIS, you can use v.edit for this. There is " snap: Snap vector features in given threshold" along with the possibility to define a box or polygon to spatially constrain the snapping to a certain area in the map as well as "where" to constrain with attribute selection.

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