QGIS – fTools-Error: “…invalid geometry…”

geometryqgisvector

I want to intersect contours with polygon like in the image below. But I got this error:

Warnings:
GEOS geoprocessing error: One or more input features have invalid geometry.
Some output geometries may be missing or invalid.

I don't know what's wrong with my geometries. I even don't know, where to search. I tested it also with a simple single-line. Same thing happened.
The result: a empty shapefile

enter image description here

What should I do now? Where can I expect an invalid geometry? Or is it because of the shapefile (OGR ESRI)? Please help!

Best Answer

I have encountered the same problem elsewhere. Reset the CRS. Go to Settings>Project Properties> CRS and Set a Reference system again. This should do the job. If not, export it as an ESRI shapefile.

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