QGIS » QGIS Application

Paste also the result geometry from ArcGIS.

Nyall Dawson wrote:

Thanks - that's helped me track down a possibly related bug in geometry collections. Looks like that intersection operation results in a collection of a string and polygon.

Can you please confirm which tool/processing algorithm/menu item you are using to perform the intersection? That will probably need to be updated to handle this case.

Originally this WKT was taken from a Shapefile. This problem (empty geometry) occured, when using:

QGIS Menu -> Vector -> Geoprocessing Tools -> Intersect

The second approach (resulting in invalid GeometryCollection) was using Python Scripting in QGIS:

    layer1 = iface.addVectorLayer(first_file, "first_layer", "ogr")
    layer2 = iface.addVectorLayer(second_file, "second_layer", "ogr")
    iter1 = layer1.getFeatures()
        for feature1 in iter1:
            geom1 = feature1.geometry()
            for feature2 in iter2:
                geom2 = feature2.geometry()
                if geom1.intersects(geom2):
                    geomintersect = geom1.intersection(geom2)
                    print "%s" % (geomintersect.exportToWkt())

Resulting Geometry in ArcGIS is (Polygon only, since input have been 2 polygons and intersecting line of inner rings has no area, thus is no polygon):

Polygon ((32363272.96124353259801865 5467641.60817768704146147, 32363283.20226028189063072 5467556.08088038489222527, 32363090.88836603984236717 5467558.03823467809706926, 32363089.01425448805093765 5467625.93344997335225344, 32363196.67524027079343796 5467660.39072373043745756, 32363272.96124353259801865 5467641.60817768704146147),(32363108.6939999982714653 5467581.39590000081807375, 32363262.36500000208616257 5467580.39589999988675117, 32363173.82899999991059303 5467597.48589999973773956, 32363160.21000000089406967 5467594.69590000063180923, 32363157.51599999889731407 5467596.38389999978244305, 32363156.73499999940395355 5467598.88590000104159117, 32363158.03199999779462814 5467602.30690000019967556, 32363160.68400000035762787 5467605.09289999958127737, 32363150.1810000017285347 5467599.87690000049769878, 32363135.58999999985098839 5467593.77389999944716692, 32363124.54699999839067459 5467587.28889999911189079, 32363108.6939999982714653 5467581.39590000081807375))

Adrian Klink wrote:

Polygon only, since input have been 2 polygons and intersecting line of inner rings has no area, thus is no polygon

Since I mentioned that ArcGIS and QGIS behave different on intersections of polygons (result is polygon only in ArcGIS) there is also a second case (I currently have no example, but I may provide one next week):

• ArcGIS: no intersection (touching line string has no area - thus no polygon)
• QGIS: intersection resulting in a line string (same behaviour as with above case which was resulting in a GeometryCollection of Polygon and LineString, but this time the outer ring and not the inner rings are affected)