Creating an intersecting linestring layer from two polygon layers using some toleranc

[المشرف العام]

I have two postgis layers:

• The first layer contains the sidewalks of my town (polygons in blue).
• The second one contains the pavements (roads) of my town (polygons in brown).

The map looks like this in QGIS with both layers activated:



Ok, now I have to obtain a layer with the curbs (lines) in the town starting from these two layers. The new layer must be composed of linestrings. Each element in this new layer should be a linestring where every of the greometries of the two layers intersect.

In the following snapshot I manually painted the geometries that should be created in this particual area:



Sorry about my bad pulse. I hope it helps to understand me better.

Ok, if I just add the layers to QGIS, for example, and intersect one layer with another I get the following layer:



The new green layer is the obtained curbs layer. I have two snags with this layer:

• It is composed of polygons
• Not all the curvs are drawn.

With this last evidence I discover that the sidewalks and roads layers were not precisely delineated one next to the other, so I need some kind of tolerance in the operation to get the layer I am looking for. As I told before it should be a linestring layer.

I think that I need some expert help to solve this...

I don't mind if the query is directly done in postgis or using QGIS or other software's tools, I just can't figure out right now how to solve this...

Thanks in advance.



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