>gLine = QgsGeometry.fromPolyline( [ QgsPoint(1,1), QgsPoint(2,2) ] ) ># buffer with distance 0.5, use 5 segments to approximate curves >gBuffer = gLine.buffer(0.5, 5) >print gBuffer.asPolygon()
The buffer() method is a great starting point to create a geoprocessing plugin. At the moment we want to implement a geoprocessing plugin with functions like buffer, union, difference etc. At the moment we realised it with Shapely. But this approach with third party libs is not nice and would be obsolete when QGIS offers the mentioned methods. QGIS native methods() based on GEOS would be the much better approach! What are your plans? Do you plan to implement union(), difference(), intersect() and relate() as QgsGeometry methods? A second question. I want to create a dissolved buffer polygon. To achieve this it is neccessary to combine all single objects p.e. LineStrings to one MultiLineString before buffer(). How do I concatenate single Linstrings into one Multilinestring? Best Regards Horst ------------------------------------------------ Dr. Horst Düster GIS-Koordinator, Stv. Amtschef Kanton Solothurn Bau- und Justizdepartement Amt für Geoinformation SO!GIS Koordination Rötistrasse 4 CH-4501 Solothurn Telefon ++41(0)32 627 25 32 Telefax ++41(0)32 627 22 14 mailto:[EMAIL PROTECTED] http://www.agi.so.ch -----Ursprüngliche Nachricht----- Von: Martin Dobias [mailto:[EMAIL PROTECTED] Gesendet am: Mittwoch, 16. Januar 2008 23:41 An: Richard Duivenvoorde Cc: [EMAIL PROTECTED] Betreff: Re: [Qgis-user] python plugin action vs mode tool On Jan 16, 2008 8:42 PM, Richard Duivenvoorde <[EMAIL PROTECTED]> wrote: > > My 'problem': I've build a sort of XY-Info tool plugin, like the raster > info plugin in the repository. But mine is suppossed to be a tool like > the zoom tool, or the select tool: you click on the tool/plugin-button, > the button gets activated/surpressed/darker, and keeps in that state > until you select one of the other (zoom, select or info) tools. Current > plugin-buttons do not get 'activated', when you click the plugin button > it doesn't stay visually(!)'active', it's a clickclack button. To get the behaviour the only thing you have to do is to call map tool's setAction() or setButton() method. That will cause that when the tool is activated/deactivated, the associated action or button will get selected/delected. (This behaviour is implemented in QgsMapTool::activate() and QgsMapTool::deactivate() so that's why it's good to call them also if you reimplement these methods.) > But still some details were not clear for me: for example it's not clear > for me if you must make a new 'tool' when you want to make a plugin > which does something with a click in the mapcanvas. No, you can use ready-made QgsMapToolEmitPoint tool and just connect to its gotPoint signal. > Another question is > the one about keeping a button 'activated'. I hope that one got answered above. > My idea is to make some 'plugin-stubs' for different kind of simple > plugins: eg starting with a very simple plugin which does not have an > interaction with the map, to a tool like the xy-info tool which must > handle a mouse click, and finally your copyright-plugin which was really > helpful for me. > But maybe a plugin stubb is not what I'm looking for: it's either to > complicated because you want to make it technically useful, or it's to > simple to be functionally useful. The idea was to hand beginners the > first steps to to a really easy plugin. Probably the best way would be to create the same "starting" plugin as the template plugin written in c++. For the rest I think it's better to use code snippets... > But maybe we need a code-snippets wiki page with questions like: > - I want to keep de plugin button activated > - I want to get hold of the active geometries of the active layer > - I want to loop through all geometries of this layer > - How do I test the type of a geometry > - How do I make pixel coordinates from world coordinates and vice versa > - How can I add a label to a (new) layer > - How can I add a new geometry to a layer > - How can I keep some project info by writing it to a project file > etc etc. > ... I should start this page myself maybe ... Well, some of those are already on PythonBindings wiki page, however some are probably missing :) I'll see what more could I add. For sure you can start a list of such simple tasks, we could address them with the code snippets. > ps (referring to my buffer questions a while a go) if you point me to > some 'easy' buffer algorithms, I'm ready to give C++ a try :-) ) Uhm, starting from r7986 you can use QgsGeometry::buffer() function that does exactly what you need :-) Obligatory snippet: gLine = QgsGeometry.fromPolyline( [ QgsPoint(1,1), QgsPoint(2,2) ] ) # buffer with distance 0.5, use 5 segments to approximate curves gBuffer = gLine.buffer(0.5, 5) print gBuffer.asPolygon() Enjoy! Martin _______________________________________________ Qgis-user mailing list Qgis-user@lists.qgis.org http://lists.qgis.org/cgi-bin/mailman/listinfo/qgis-user
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