How to reverse vertex ordering in polygons?

Question

I am working with an Oracle spatial connection in QGIS through which I am accessing and editing a vector layer. I find that when I edit a geometry, the vertex ordering is reversed (to clockwise in the outer ring) which then gets flagged up as an error in oracle.

I am using the combine function (http://www.qgis.org/api/classQgsGeometry.html) among others in my own editing tools, but I notice that this happens with the native merge polygons tool too.

I think this reo-ordering to clockwise is the default in QGIS based on this link: https://hub.qgis.org/issues/6283 and was wondering if there is a way to reverse it to counter clockwise? (preferably with python)

Answer 1

Maybe overdone, but these post might contain some useful hints:

How can I switch line direction in QGIS?

Switch line direction for PostGIS-lines in QGIS or Pgadmin

In PyQGIS the code mentioned there is still valid, I think:

geom = feature.geometry()
nodes = geom.asPolyline()
nodes.reverse() 
newgeom = QgsGeometry.fromPolyline(nodes)
layer.changeGeometry(feature.id(),newgeom)

Since QGIS comes with GRASS support, have a look at v.edit tools=flip https://grass.osgeo.org/grass64/manuals/v.edit.html

[current QGIS version 2.14.5.LTR]