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5 Topology management

For creating, analyzing and repairing topology of vector data the modules v.build as well as v.clean are available.

v.build

The module v.build is the successor to the module v.support known from GRASS 5.4. It makes the reorganization of the topology possible which is normally completed automatically. Furthermore, it contains so called DUMP functions which pass information concerning the topology or 'spatial index' to standard output.

v.clean

The module v.clean allows a user to change and/or repair the topology of a vector file. At present, twelve topological operations are offered which are briefly introduced.

break: breaks overlaying lines at their intersection points and displaces them by a node.

rmdupl: deletes lines that occur twice. Please handle the attributes with care.

rmdangle: deletes so called dangles. Please consider the indication of the threshold.

chdangle: changes the data type of the so called dangles from boundary into line. Please consider the indication of the threshold.

rmbridge: deletes topologically illegal connections between an area and an isle or between two isles.

chbridge: changes the data type of a connection between an area and an isle or two isles from boundary into line.

snap: depending on the threshold lines are connected with the next following vertices.

rmdac: deletes centroids in polygons that occur twice.

bpol: 'topological clean-up' of data, which do not have their own topology (e.g.: SHAPE). Creating a new topology with clean vertex-to-line transitions.

prune: deletes vertices depending on the indicated thresholds of lines and boundaries without changing or damaging the topology.

rmarea: deletes micro areas depending on the indicated thresholds and allocates them to the biggest adjacent area.

rmsa: makes small angles disappear between lines and nodes.