________________________________ Lähettäjä: Michaël Michaud [michael.mich...@free.fr] Lähetetty: 16. maaliskuuta 2012 22:44 Vastaanottaja: jump-pilot-devel@lists.sourceforge.net Aihe: Re: [JPP-Devel] Combining polygons
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. Good question indeed. It took awhile to repeat it. This is somehow related to EZ-Buttons shortcut. The shortcut seems to remember, not only the menu selection it is connected with, but also the state of OJ project when the shortcut was created. It can be created by opening some layer to OJ and making is editable so thet combine two polygons is working. Create the EZ-Button shortcut now and add a new layer. Now the EZ-Buttons shortcut combines polygons even the layer is not editable. So this is a feature in the EZ-Buttons. - "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. In my case I want that the new areas are also continuos. Sometimes multipolygons would be acceptable. Perhaps there could be a check box for cases when features selected for combining are all simple polygons "Allow multipolygons as new features? ". If selection already contains multipolygons then the result can naturally contain them too. > 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. Yes, this is the case. All the polygons in the layer are adjacent and all together would be a monster polygon with thousands of holes and hundreds of thousands of vertices. I am going to reduce the number of polygons into about 500 and I want all them to have some reasonable amount of vertices. Automatic system by using some grid layer as a helper layer for splitting data into rectangular pieces first to be unioned later tile by tile would not give directly a good result. Data is from archipelago and in some places there is just open sea and in other places masses of islands. I will get the job ready faster by doing the selections manually. "Union selected in place" tool would make it more convenient, though. > 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) Sounds doable, I will try it next week. -Jukka- > Michaël -Jukka Rahkonen- ------------------------------------------------------------------------------ This SF email is sponsosred by: Try Windows Azure free for 90 days Click Here http://p.sf.net/sfu/sfd2d-msazure _______________________________________________ Jump-pilot-devel mailing list Jump-pilot-devel@lists.sourceforge.net<mailto:Jump-pilot-devel@lists.sourceforge.net> https://lists.sourceforge.net/lists/listinfo/jump-pilot-devel ------------------------------------------------------------------------------ This SF email is sponsosred by: Try Windows Azure free for 90 days Click Here http://p.sf.net/sfu/sfd2d-msazure _______________________________________________ Jump-pilot-devel mailing list Jump-pilot-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/jump-pilot-devel
