How to align directions of connected lines?

Question

I have a vector line made of different pieces of lines with different directions. I merged the lines to one. But this merged line still have different direction in its "invisible" parts. I want to plot a profile, so I need ONE direction. Any idea?

Answer 1

Both qgis and GRASS have tools to switch line direction. In QGIS you need the (experimental) plugin Swap Line direction. In GRASS you can use the v.edit module with "tool-flip" However, in both cases, you'll have to manually select which line segments to flip, and which to leave as they are. I don't think there's any way around that.

Answer 2

Not sure if it will work for you, but can you create a topology with a sink at the end of the line in the direction you want the line to run?