EuroSDR Projects - Host Ireland

3 Reference Data
In order to have a basis for analyzing the interpretations produced as part of the contest, it was
necessary to create reference data sets for the different test sites. Reference data contents should
ideally include information from optical and SAR imagery, as well as information from topographic
maps, accounting for the fact that visual interpretation of image data alone – as conducted by test
participants – can only achieve an image-specific interpretation of reality excluding non-image
information. Therefore, the outcome of reference data compilation was mapping content considered
optimal for the tests purposes from a mapping experts’ point of view – admittedly to a certain degree a
subjective view point. This data was used as the basis for comparing participants’ results.
3.1 Generation of Reference Data
The scanned and the digital topographic maps had to be registered with the corresponding optical and
SAR images. For reasons of simplicity, geometric reference was taken from the optical images to
register the maps. After registration, the maps were geometrically compatible with optical and SAR
imagery. However, quantitative (pixel-accurate) interpretations of georeferenced topographic maps
were not possible due to inaccuracies of these types of maps. They were only used to examine the
content.
Reference data were generated using the vector-based desktop GIS software ArcView of ESRI.
Information from SAR and optical data were overlayed and were used to produce an exact reference
map; missing information was obtained from the topographic map. Interaction and thorough processing
guaranteed highly accurate reference data for all data sets (Figure 6). To avoid a bias of the
reference maps with respect to optical or SAR imagery the reference information was extracted from
both sensor’s images on equal terms.
192
Figure 6: From three basic information sources to the reference map (left: optical image,
topographic map, SAR image; right: reference map of Copenhagen)