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QGIS v2.x plugin for prepair. The binary of prepair must be installed on your system---we offer Windows 64bit binaries, and a CMake makefile to easily compile binaries for Mac and Linux.

It permits you to automatically repair single polygons. Simply select one vector layer (containing polygons), and launch the plugin. You can then decide to repair only the selected polygons, or only those invalid (with perform validation with GEOS). Repairing a valid polygon will mean that its geometry might be changed (e.g. the first point in a ring could be a different one).

The output of prepair is new layer (always a shapefile at this moment). Each input polygon becomes a new object in the new layer, with its original attributes. If an invalid polygon, once repaired, is composed of 2+ polygons (e.g. if a bowtie polygon was the input, then 2 valid polygons are created), then only one geometry is created: a MultiPolygon.

Automated repair methods can be considered as interpreting ambiguous or ill-defined polygons and giving a coherent and clearly defined output. Examples of errors are: polygon has a dangling edge; polygon is not closed; polygon self-intersects; an inner ring of the polygon is located outside the outer ring; etc. We offer two repair paradigms:

1. odd-even: an extension of the odd-even algorithm to handle GIS polygons containing inner rings and degeneracies;
2. setdiff: we follow a set difference rule for the rings.