European Organization for Experimental ... - Host Ireland

To perform this trial it was necessary to have the raster map, aerial ortho-images and
IKONOS images in a common map projection. Each data set was adjusted to the Swiss coordinate
system (Reference System - CH1903 / Ellipsoid – Bessel 1841) using ERDAS
Imagine software. Once these were established it was possible to overlay each set of data for
comparison. It was also possible to load the imagery into L/H Systems SOCET SET and
ERDAS Imagine. For feature extraction the Annotation functionality was used in ERDAS
Imagine. This enabled each feature type to be captured in a separate layer, with the end
product being a simple vector map, without detailed attributes. Note that, at the time of this
project, it was not possible to orthorectify IKONOS imagery using standard software packages,
since the characteristics of the IKONOS sensor were not publicly available. The
image subsets were therefore warped to fit the map detail (as discussed below in section
3.3).
Within each subset, a manual survey of the area was performed, keeping to the Ordnance
Survey data capture specification as far as possible. The resulting features were compared
with the features on the 1:25 000 map, which was taken to be the true picture of the area.
2.3 Results.
Below is a summary of the results, compiled from the findings in each area. Errors of omission
and commission are represented as follows: The second column indicates the percentage
of “known” features on the map which were correctly identified in the imagery (e.g.
80% of the building outlines present in the map were correctly identified as buildings in the
image). The third column indicates the percentage of features which were mis-identified in
the image (e.g. 10% of the features captured from the image as buildings were not present as
buildings in the map). This means that the two numbers relate to slightly different things
and will not therefore add up to 100%.
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