Geo Toolkit – Data Quality Tools

Geo Toolkit is a set of data quality tools. They were developed for customers who need to adjust users' geographic data in case their existing geographic base layer had changed  (e.g. orthophoto base layer). At GIS solutions a lot of users' data are snapped to orthophoto base data layer. Whenever a base data layer is improved by reaching a higher precision then users' data no longer match with it. Geo Toolkit package provides three tools which help users to solve such inadequacies.

• GeoCheck: verifies geo-data validity,
• GeoMorph: automated tool for shifting polygons,
• GeoClone: tool for checking and adjusting polygons created by GeoMorph.

Geo Toolkit’s advantages:

• simultaneous processing of a great number of inter-connected data entries,
• time optimization: similar tools require several weeks for the same amount of data, however Geo Toolkit reduces such a procedure to a few hours,
• effective processing and handling of topological errors in the data.

GeoCheck is a  spatial data verifying tool which helps to identify any data errors. An output dataset is produced, containing locations of errors and their descriptions. GeoCheck checks a shape-file for any errors, including:

• overlap (two geometries' intersection is non-zero)
• gaps (non-covered space exists, surrounded by other geometries)
• spikes (a spike is a very sharp angle on a polygon boundary or on a polyline; usually that means an error)
• kick-backs (a kick-back is similar to a spike, but with slightly different criteria)
• area (polygons with really small areas are usually errors)
• length (lines with really small lengths are usually errors)
• self-intersections (the boundary of a polygon may not intersect itself, nor can a polyline intersect itself)
• overlapping holes (another hole exists within a polygon hole)
• unclosed rings (polygon boundaries must be closed)

GeoMorph is a »quick-fix« tool which adopts user data e.g. graphic polygons in relation to the changed base data layer.

The software compares two sets of geometries of spatial data and tries to snap lines from the first set to the second set. It works by examining user geometries and matching them with the base data layer geometries; if a part of the user geometry is not snapped to the base data layer, but the adjacent parts are, automatic effort is made to also snap the previously non-snapped part. The maximum distance between the original and the snapped lines is configurable, so the user is able to limit the change of geometries.

Because of deficient source data there are usually many vectors missing that should be present at the base data layer. As a consequence the vector data that are produced with GeoMorph through the base data layer may not be very precise. For this reason the geometries that get shifted might look odd and don't match well with the improved base data layer. To improve the results of this process, a separate pass has to be done by using GeoClone tool.


Figure 1: Results of a topology check. Error locations are calculated and can be displayed on a map along with detailed descriptions of the type of error.

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