How to unpolygonize and remove outermost border?

Question

QGIS has "polygon to line" but this isn't exact reverse engineering of "line to polygon". I want no overlapped border closed lines, just segmented (on each intersected point) lines.

Additionally I want to remove to outermost boundary (if it can be automatically done).

Example: in the case of a kite shape (4 triangle polygons) will turned into inner skeleton cross lines (4 segments)

Answer 1

had a similar problem and got help here: How do I split polygons into line segments?. afterwards delete the "outer" lines

Answer 2

I found more another way using sextante entirely

1. polygon to line
2. v.clean > break/bpol
3. v.clean > rmdup

rmdup will return two result: outer and the inside (without overlapped segments)

Answer 3

You could get partway to the solution with QGIS and the GRASS plugin; unfortunately the select tool doesn't let you select only internal lines (as suggested by @Conor) so removing the outermost boundary would be tough.

In QGIS 1.8, if you have a layer A, to split the polygons into single, non-overlapping lines:

1. Polygons to lines giving A_lines;
2. Using GRASS plugin, v.split A_lines (with 1 segment option) to give single segments A_lines_single;
3. Delete duplicate geometries with the MMQGIS plugin (MMQGIS | Modify menu) giving A_lines_single_unique.

Answer 4

There is a option available in Sextante box called V.clean perform this and use polygoniser plugin option .I think when you use V.clean it will remove unwanted topological error in lines .Then use Polygoniser to convert lines to polygons.