EuroSDR Projects - Host Ireland

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Figure 4-16: Change maps of Swiss data sets
The change maps were evaluated by swisstopo by visual comparison with the new VECTOR25 data. The basic
requirements of swisstopo for a change detection system are that the rate of objects wrongly detected as new must
be below 25 % while the rate of new object correctly detected must be 100 %. The conclusion of the evaluation
were that too many new areas were detected as new even though they were not new, new forest areas were not
clearly identified and no optimal results for water could be achieved. In addition it was noted that as long as the
swisstopo vector data set is based on map information (two steps of interpretation) accuracy problems (geometry
and semantic) will remain (e.g. streets). Possible improvements might be achieved by better tuning between
swisstopo categories and detected categories and road buffering. In addition, individual buildings should be used
(not available for this study) instead of the data for built up areas employed here.