1. Research Associate, Institute of Flight System Dynamics, RWTH Aachen Univ., Wuellnerstrasse 7, 52062 Aachen, Germany (corresponding author).
2. Research Assistant, Dept. of CAD & Planning Methods in Urban Planning and Architecture, Univ. of Kaiserslautern, Pfaffenbergstrasse 95, 67663 Kaiserslautern, Germany.