[Gfoss] Problema: da linee a poligoni

[stefano campus]

pcav wrote
> puoi descrivere in dettaglio l'operazione desiderata?
> grazie.
> 
> -- 
> Paolo Cavallini - www.faunalia.eu

scopo del gioco è trasformare una polyline chiusa in un poligono
dxf o shape linestring come input (input)

1) [qgis dev] vector-->geometry tools-->lines to polygons
(out_qgis_lines2polygon) 
2) [saga 2.2.3] shapes-->polygons-->convert lines to polygons
(out_saga2.2.3_lines2polygon)
3) [grass 7.0.3] v.type (out_grass7.0.3_v.type)
4) [arcview 3.1] xtools extension --> make polygons from line
(out_arcview_xtools)

come potete notare i primi tre danno lo stesso risultato; solo arcview dà il
poligono corretto  :-(

polylines2polygons.zip
<http://www.mediafire.com/download/tbutzmicq19bi1k/polylines2polygons.zip>  

ecco quanto riportato nel manuale dell'estensione xtools 
This script converts selected polylines in a theme to one single part
polygon, and stores it in a new shapefile.
If no polylines are currently selected, all polylines in the theme will be
processed. The polylines do not need to be snapped together. Gaps between
polylines will be bridged with a straight line. Source polylines can be
single part, multi-part or mixed in the theme. Neither the order of the
polylines in the FTab, nor the order in which the polylines are selected is
important.
If polylines from more than one theme will be used to build the polygon, the
user will need to assemble the necessary polylines in a separate theme
before running this script. A common example of this situation is the
necessity to build a polygon from lines borrowed from PLS, Roads, Streams
... themes. If there are gaps between the source polylines that should not
be bridged with a straight line, the user should digitize in polylines to
fill the gaps prior to running the script. This script differs from the
ArcInfo Build command (polygon option) in that only one polygon can be built
in a single operation.
XTools checks the input theme for intersections, places where lines cross
without a break at the crossing point. XTools will break the lines at the
crossing points, but this results in ''dangles'', pieces of line (usually
short) that will create a problem in the output polygon if not eliminated.
If intersections are detected, XTools will create a new polyline theme with
the lines broken at crossing points and with the crossing points marked with
a red graphic. The user needs to manually delete the dangles related to the
line crossings and then rerun the script on the new polyline theme.




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