Hi,
I started to reduse the number of polygons in one dataset which
originally it contained more than 5000 rahter complicated polygons.
Some experience:
- "Combine two selected polygons tool" is fast but it has a little
bug. It allows to combine polygons even if the layer is non-editable.
How do you do that ? Menu item is inactive (grayed) if layer is non
editable.
- "Combine polygon with neighbouring polygon" is very slow and can
give an out-of-memory error. Is it perhaps walking through all the
features when searching for the one to use for combining? I would
guess that it should be much faster if it correctly selects just the
few adjacent polygons for candidates first.
I think the algo of this plugin is not so simple... I think Stefan know
it better
- Making union of selected features suits me well because I would like
to combine about 10-20 polygons together. However, because it creates
new layer each time there is some extra work with joining them
together later.
- "Union selected in place (if result can be simple polygon)" would be
the ideal tool for just this case.
Agree, this would be helpful. Not sure I would limit to simple polygons
though.
I suppose you don't want to union all adjacent polygons, otherwise, the
simplest is to union the whole layer, then to explode the multipolygon.
Michaël
Here is a workaround (didn't check it though)
- create a second layer.
- draw 1 linestring per group of building, intersecting all buildings
you want to aggregate (and only those one)
- create an auto-increment attribute on these linestring layer
- do a spatial join to transfer linestring id to polygons
- union polygons by attribute
(you will get a multipolygon with all polygons not intersecting a
linestring : explode it)
-Jukka Rahkonen-
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