Is there a simple way to calculate a field in QGIS indicating if the vertices of each polygon feature in a layer are in clockwise or anti-clockwise direction?
For simplicity, lets assume the layer has multiple polygon features, with a single geometry per feature (no multifeatures/multipolygons), and without donuts or other complications.
I have found related questions, but none of them give an answer to my question.
These ones are ESRI specific:
This one resolves the problem from a math point of view, but not applied to QGIS
The same algorithm is implemented in a shapely function - see links provided by Andreas Muller:
signed_area
: toblerity.org/shapely/shapely.algorithms.html. Polygons the must be read into a Python-Data-Structure and the first ring must be extracted. But anyway: all outer rings of polygons in a shapefile have the same orientation: clockwise.