Hello
My name is Javier Sanchez and I'm the developer of a QGIS based standalone
application to convert Spanish Cadastre data to OpenStreetMap format [1].
I'm trying to port this app from QGIS 2 to 3 and I would like this to work
also with the previous version.
In QGIS 2.x, I was able to write a shapefile with a mixed set of polygons
and multipolygons geometries. Now in QGIS 3.x I can't. Maybe this is a GDAL
issue. Probably the last behaviour is the correct one. But is there any way
in QGIS 3 to create a shapefile mixing polygons with multipolygons?
Here is an example code to illustrate what I meant:
crs = QgsCoordinateReferenceSystem(32628)
fn = 'xxx.shp'
w = PolygonLayer.create_shp(fn, crs)
p = [[QgsPoint(0,0), QgsPoint(1,0), QgsPoint(1,1), QgsPoint(0,0)]]
mp = [[[QgsPoint(2,0), QgsPoint(3,0), QgsPoint(3,1),
QgsPoint(2,0)]],
[[QgsPoint(4,0), QgsPoint(5,0), QgsPoint(5,1),
QgsPoint(4,0)]]]
f1 = QgsFeature(QgsFields())
g1 = QgsGeometry().fromPolygon(p)
f1.setGeometry(g1)
w.addFeature(f1)
f2 = QgsFeature(QgsFields())
g2 = QgsGeometry().fromMultiPolygon(mp)
f2.setGeometry(g2)
w.addFeature(f2)
del(w)
l = QgsVectorLayer(fn, 'test', 'ogr')
for f in l.getFeatures():
g = f.geometry()
print(g.isMultipart())
When I run this in QGIS 2, the output is:
False
True
When I run the same example in QGIS 3.x (replacing fromPolygon with
fromPolygonXY and fromMultiPolygon with fromMultiPolygonXY), the output
instead is:
True
True
The writer converts g1 from polygon to multipolygon and every geometry in
the resulting shapefile have the same type while before I had a bunch of
multipart and singlepart geometries.
Regards, Javier
[1] https://github.com/OSM-es/CatAtom2Osm
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