Renaturalization of Parts of the National Park Neusiedler See-Seewinkel 
63 
Fig. 2: Area of interest near the Neusiedler See plotted on the Austrian topographic map, original scale 1:50.000. 
[source: Austrian Federal Office of Meteorology and Surveying, publishing rights requested] 
3.3 Georeferencing 
After the flight the recorded positioning data have to be analysed in a post processing step. Then, for each laser point the 3D co 
ordinates can be calculated, first as polar co-ordinates, finally as XYZ co-ordinates of a global (reference) system. 1 
Surfaces derived from laser scanning data may show Z-discrepancies in overlapping regions of adjacent flight strips. Their magnitude 
in the current project was a few decimetres, big enough to seriously impair the quality of results where shallow water levels are 
crucial parameters. 
The deformations probably originated in orientation deficiencies of the GPS or INS system. Photogrammetric block adjustment 
provides an appropriate tool for minimizing discrepancies of that kind. Each individual laser scanning strip serve as "model" for the 
adjustment where additional parameters in form of polynomials are applied to model systematic GPS or INS errors. For connecting 
the strips to one uniform block tie information is needed. The conventional photogrammetric way of observing well-defined tie 
points in overlapping areas cannot be pursued in the case of laser scanning data which are, according to the acquisition principle, 
irregular samples of elevation information. A work-around is possible by defining small surface patches in areas where tie 
information is required. With the help of those patches homologous points can be determined. Control points, i.e. points with known 
XYZ co-ordinates, allow the transformation of the entire block into the global (reference) co-ordinate system. It can be carried out in 
one adjustment step together with fitting the strips to each other. 
If the correction of the above mentioned height discrepancies were neglected, the result, i.e. the digital terrain model, would slightly 
be shifted in the affected regions. In the current project the height differences of the homologous patches were ± 9.4 cm before 
adjustment and ± 3.6 cm after adjustment (95% probability). The method of adjustment is described in more detail in (Kager & 
Kraus, 2001), while the results will be discussed in (Horvath, 2001). 
1 As global co-ordinate system the European Terrestrial Reference System 1989 (ETRS 89) was chosen. In the course of a Phare 
project for the Hungarian part of the Neusiedler See data (topographic maps, orthophotos, land register, etc.) were transformed to the 
same European co-ordinate system. In this manner a Nationalpark GIS can be used for analysis and planning across national borders. 
The responsible person for the Phare project was Dr. Markus. The transformation of the Hungarian data to the ETRS 89 was 
performed by Dr. Bacsatyai and DI Kiraly. They are all members of the University of West Hungary. The appropriate preparatory 
work for the georeferencing in the Austrian part was performed by DI Titz (Department of Advanced Geodesy, Vienna University of 
Technology), Dr. Erker (Austrian Federal Office of Meteorology and Surveying) and DI Mandelburger (Institute of Photogrammetry 
and Remote Sensing, Vienna University of Technology).