As some authors have
reported lidar errors to increase with off-nadir scan angle
(e.g. Baltsavias, 1999a), we selected marker locations as
close as possible to the centre of each of the nine swaths
comprising the full dataset. GCP extraction was therefore limited to a zone 200m either side of the swath centre,
representing 25% of the full swath width either side of the
nadir point (assuming an average width of 783 m).