On 6/16/20 4:17 PM, Tudorache, Marian wrote: > Hi everyone, > > I have a list of polygons given by a list of points. > The polygons are properly drawn on QGIS canvas by creating the geometries, > the each geometry is used to create a Qgsfeature which are saved on a > shapefile. > The problem appears in detecting if a point on the Earth is inside or outside > the polygon. > Using pyqgis QgsGeometry intersects function returns proper value. > However when I export the polygon to intermaphics from Kongsberg Geospatial > (former Gallium) sometime the point is inside other time is outside the > polygon. > I tried to switch the order of the points is QGIS ,but the intersects > function always give me the same result regardless of the order of the points. > In intermaphics the intersection between a polygon and a point varies with > the order of the points which define a polygon. > I talked to people from gallium and they confirmed the order of the points is > important. > In one direction a inner area of the polygon is the small surface and if I > switch the order the inner area is the outside and it wraps the Earth on the > opposite side. > > Does QGIS or pyqgis has a similar mechanism to determine which is the inner > part of the polygon on a sphere or ellipsoid?
Hi Marian, are'nt we here talking about the so called Right Hand Rule? https://postgis.net/docs/ST_ForceRHR.html says: In particular, the exterior ring is orientated in a clockwise direction and the interior rings in a counter-clockwise direction. QGIS has this also: https://github.com/qgis/QGIS/blob/master/src/core/geometry/qgsgeometry.cpp#L2651 With pyqgis you can als use forceRHR: https://qgis.org/pyqgis/3.12/core/QgsGeometry.html?highlight=qgsgeometry#qgis.core.QgsGeometry.forceRHR I do know that QGIS is not so good when a geometry crosses the world-dateline though... but I do not think that is your case is it? Or do I misunderstand you question? Regards, Richard Duivenvoorde _______________________________________________ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
