I have a polygon vector layer representing the area inundated in a flood. The layer has been produced in a such a way that some of the areas are composed of multiple smaller touching polygons (see screenshot below, labelled "original data").
I would like to dissolve the polygons where they touch. If I use the dissolve geoprocessing tool in QGIS's fTools, which uses the GEOS library, I get some unexpected results (see "dissolve with QGIS fTools"). It seems that GEOS doesn't use a threshold in determining if polygons are touching, as mentioned in these issues:
The same approach in ArcGIS gives the expected result (see "dissolve with ArcGIS 10.1").
Apparently this is a "feature" of GEOS, rather than a bug. Is there any way to fix the data I have to produce the expected result? A minor loss of precision (a few cm?) could be acceptable for me. Ideally the solution would be something I could write into a QGIS plugin, as a pre-processing step.
Related question (with no answers): How to set tolerance value of Geoprocessing tool in QGIS?
Link to sample data as a shapefile: https://www.dropbox.com/s/c8ns7wwfv289ad0/sample.zip