Is there any tool in QGIS that traces a line like the trace tool (Editor Toolbar) in ArcGIS? I want to draw a line and trace this line back so that I get the beginning and the end of the line at the same position. Any suggestions?
There is a plugin for QGIS 1.8: TraceDigitize
Author's tip: "Use ctrl-Key to trace, backspace to delete, left mouse click to set a normal vertex and right mouse click to finish. Uses the snapping options, which may be changed during digitizing (Consider opening the snapping option as dock widget)"
I do not know how to qgis, but KOSMO and OpenJUMP have a tool "autocomplete polygon". Use these GIS together!
As fausto mentioned, there is a "TraceDigitize" plugin for QGIS 1.8, however it works differently than ArcGIS Trace tool.
Once installed, you should set your snapping settings:
Settings>Snapping options. I reccomend gaving the settings open, because the tool is highly dependant on snapping options.
Then, using Trace Edit tool and holding CTRL key you can trace along existing feature lines. The tool is a bit quirky, but it's quite OK, if you mess around with snapping options. Just as ArcGis caunterpart, the tool allows you to add vertices manually, by left clicking. To undo, you should press BACKSPACE.
There is a new plug-in called AutoTrace: