[Qgis-developer] List of geometries corrupted when given as a function parameter.

[Matthias Kuhn]

Hi Vincent,

Is it possible that you are hit by the bug in this report [1]

The workaround would by to keep a reference to the encapsulating 
feature as long as you need their geometries. (Or possibly to copy the 
geometry with g = QgsGeometry( feature.gemetry() ))

Best
Matthias

[1] http://hub.qgis.org/issues/777

On Mit 15 Jan 2014 15:10:37 CET, Vincent Damoy wrote:
> Hi to all,
>
>
> I'm working with QGIS 2.0.1 on a python plugin to help users enter
> data in a Postgis database.
> Among others things, this plugin can convert selected features (from
> points to polygons, from lines to points, etc...)
>
> _The plugin :_
> operation_dialog.py is my main module.
> convert_geometries module is used to convert features
>
> In this second module, convert_geometries function accepts 2 parameters :
> geomlist (a list of geometries),
> geomoutput, (output data type : Qgis.point, Qgis.polygon ou Qgis.line).
>
> extract :
> /def convert_geometries(geomlist, geomtype):
>      ret = None
>      if len(set([geom.type() for geom in geomlist])) <> 1:
>          print [geom.type() for geom in geomlist]
>          ret = None
>      else :
>          if geomlist[0].type() == QGis.Line and geomtype == QGis.Polygon:
>              ret = linestrings_polygon(geomlist)
> .../
>
> If geometries in geomlist have different data types, then ret=None
> (and the plugin manage this error).
> Else, if features are lines and polygons are needed, corresponding
> conversion function is started.
>
> convert_geometries is started from my main module :
>
> /geom2=convert_geometries([feature.geometry() for feature in
> self.iface.activeLayer().selectedFeatures()],geom_output) /
>
> Here, geomlist is a list of geometries from features selected by user
> in the active layer).
> geomtype=geom_output (selected by user in a combobox).
>
> _The problem :_ Things go well if only one feature is selected.
> However, if 2 or more features of the same type are selected, (3 lines
> for example), geometries are systematically corrupted during passage
> from one module to the other, except the last one.
>
> In the main module, this line :
> « /print [feature.geometry() for feature in
> self.iface.activeLayer().selectedFeatures()]/ »
> returns [1,1,1] (which means [line , line, line]).
> However, in convert_geometries, «  /print [geom.type() for geom in
> geomlist]/ » line returns [3,3,1]
> (that is [unknowm geometry, unknowm geometry, line]).
> If I try to display geometries in WKT format (/print
> [geom.exportToWkt() for geom in geomlist]/), QGIS closes without an
> error message.
>
> _Question :_
> Thus, if a list of several geometries is given in function parameter,
> they seems to be corrupted (except the last, or if there is only one
> geometry)
>
> Do you have an idea of what happens ? Where is my mistake? Do you see
> tests to perform in order to diagnose this issue ? (particularly, why
> the last geometry of a list is not corrupted, unlike others ?)
>
> Thanks for advance
>
> Vincent Damoy
>
>
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