Unmanned air vehicles have been increasing in their autonomous capabilities. This research furthers these capabilities by focusing on the automation of landing site determination for rotorcraft in urban environments. Automated landing saves energy and allows the aircraft to choose areas that are safe for people and the aircraft. Two methods are used to gather information about the terrain of potential landing sites. One method is 3D reconstruction from multiple camera images. The other method uses a range sensor to reconstruct the terrain. Both of these methods create an inertial terrain map of the environment in the form of a point cloud that can be investigated for possible landing sites. Two strategies were developed to search the terrain map for possible landing sites: grid-based RANSAC and Recursive-RANSAC (R-RANSAC). Both strategies search for flat stable areas for landing. Grid-based RANSAC separates the terrain map into discrete portions for plane fitting analysis. These fitted planes are used to determine whether portions of the terrain map are suitable for landing. Two additional variations of grid-based RANSAC were explored that resulted in improvements to the approach. This strategy can quickly find landing sites from large terrain maps. The other strategy, R-RANSAC, is a recursive approach that analyzes each point in the terrain map for plane fitting. New planes are created as needed to fit points in the terrain map. Planes that fit a large number of points are analyzed for possible landing locations. This strategy is more complex to implement, but results in a simpler model of the environment: a small set of 3D planes. The results are displayed with the possible landing locations. Both landing-site strategies were implemented onboard a hexrotor aircraft and successfully demonstrated in flight.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: This thesis presents a complete state estimation framework for landing an unmanned helicopter on a ship deck. In order to design and simulate an optimal state estimator, realistic sensor models are required. Selected inertial, absolute and relative sensors are modeled based on extensive data analysis. The short-listed relative sensors include monocular vision, stereo vision and laser-based sensors. A state estimation framework is developed to fuse available helicopter estimates, ship estimates and relative measurements. The estimation structure is shown to be both optimal, as it minimises variance on the estimates, and flexible, as it allows for varying degrees of ship deck instrumentation. Deck instrumentation permitted ranges from a fully instrumented deck, equipped with an inertial measurement unit and differential GPS, to a completely uninstrumented ship deck. Optimal estimates of all helicopter, relative and ship states necessary for the autonomous landing on the ship deck are provided by the estimator. Active gyro bias estimation is incorporated into the helicopter’s attitude estimator. In addition, the process and measurement noise covariance matrices are derived from sensor noise analysis, rather than conventional tuning methods. A full performance analysis of the estimator is then conducted. The optimal relative sensor combination is determined through Monte Carlo simulation. Results show that the choice of sensors is primarily dependent on the desired hover height during the ship motion prediction stage. For a low hover height, monocular vision is sufficient. For greater altitudes, a combination of monocular vision and a scanning laser beam greatly improves relative and ship state estimation. A communication link between helicopter and ship is not required for landing, but is advised for added accuracy. The estimator is implemented on a microprocessor running real-time Linux. The successful performance of the system is demonstrated through hardware-in-the-loop and actual flight testing. / AFRIKAANSE OPSOMMING: Hierdie tesis bied ’n volledige sensorfusie- en posisieskattingstruktuur om ’n onbemande helikopter op ’n skeepsdek te laat land. Die ontwerp van ’n optimale posisieskatter vereis die ontwikkeling van realistiese sensormodelle ten einde die skatter akkuraat te simuleer. Die gekose inersie-, absolute en relatiewe sensors in hierdie tesis is op grond van uitvoerige dataontleding getipeer, wat eenoogvisie-, stereovisieen lasergegronde sensors ingesluit het. ’n Innoverende raamwerk vir die skatting van relatiewe en skeepsposisie is ontwikkel om die beskikbare helikopterskattings, skeepskattings en relatiewe metings te kombineer. Die skattingstruktuur blyk optimaal te wees in die beperking van skattingsvariansie, en is terselfdertyd buigsaam aangesien dit vir wisselende mates van skeepsdekinstrumentasie voorsiening maak. Die toegelate vlakke van dekinstrumentasie wissel van ’n volledig geïnstrumenteerde dek wat met ’n inersiemetingseenheid en ’n differensiële globale posisioneringstelsel (GPS) toegerus is, tot ’n algeheel ongeïnstrumenteerde dek. Die skatter voorsien optimale skattings van alle vereiste helikopter-, relatiewe en skeepsposisies vir die doeleinde van outonome landing op die skeepsdek. Aktiewe giro-sydige skatting is by die posisieskatter van die helikopter ingesluit. Die proses- en metingsmatrikse vir geruiskovariansie in die helikopterskatter is met behulp van ’n ontleding van sensorgeruis, eerder as gebruiklike instemmingsmetodes, afgelei. ’n Volledige werkingsontleding is daarna op die skatter uitgevoer. Die optimale relatiewe sensorkombinasie vir landing op ’n skeepsdek is met Monte Carlo-simulasie bepaal. Die resultate toon dat die keuse van sensors hoofsaaklik van die gewenste sweefhanghoogte gedurende die voorspellingstadium van skeepsbeweging afhang. Vir ’n lae sweefhanghoogte is eenoogvisie-sensors voldoende. Vir hoër hoogtes het ’n kombinasie van eenoogvisie-sensors en ’n aftaslaserbundel ’n groot verbetering in relatiewe en skeepsposisieskatting teweeggebring. ’n Kommunikasieskakel tussen helikopter en skip is nie ’n vereiste vir landing nie, maar word wel aanbeveel vir ekstra akkuraatheid. Die skatter is op ’n mikroverwerker met intydse Linux in werking gestel. Die suksesvolle werking van die stelsel is deur middel van hardeware-geïntegreerde simulasie en werklike vlugtoetse aangetoon.