GeoTools

Star-Apic Ltd., UK

The aim of the contract was to develop tools for error checking of GIS data and correction of the data.

GeoTools were developed for Star Apic because their customers needed a tool that could adjust users' data when their national Ordnance Survey (OS) data changed. The need occurred when a large amount of user data had been snapped on OS data, and then the OS improved their precision so the user data no longer matched OS.

GeoTools includes three tools:

• GeoCheck (verifies geo data validity)
• GeoMorph (automated tool for drawing polygons)
• GeoClone (tool for checking and adjusting polygons created by GeoMorph)

GeoCheck is a tool for verifying shapefile data of any errors. An output file is produced containing locations of any errors and their descriptions. GeoCheck checks a shapefile for any errors. GeoMorph takes a set of geometric data and a set of vectors to produce the data shifted by a vector field approximated from the vector set. The vector field is produced by Delauney triangulation of vector source points, producing a relatively high-quality output. After the vector field is established, the user geometries are first snapped to original OS data, then shifted, and finally snapped to improved OS data. The results on every step are recorded and several metrics are computed, so the user is able to verify anything that may be suspicious (for example, if the area changes by 150%, something is usually wrong). Unfortunately, the vector data that OS produces are not very good, as many vectors that should have been present are missing; the result is that the geometries shifted often look odd and don't match the improved OS very well. To improve the results, a separate pass is done on the data using GeoClone.