GNSS terrain obstacle modelling using fisheye lense for smartphones

The GNSS methods of precise positioning are nowadays widely used despite the fact that the accuracy and reliability of those methods are limited to open sky localizations. The presence of terrain obstacles, for instance in urban, mountain or forest environments, significantly effects the accuracy of GNSS measurements due to signal reception blockage and the multipath effect. In case of such hard observational conditions an accurate mission planning is still essential despite the large number of satellites in GNSS systems constellations. Currently there is a variety of mission planning software. Most of those applications allow to create hand-drawn polar obstruction diagrams. This task can be performed more accurately by applying some semi-automated terrain obstacles modelling methods. Hemispherical photography, despite its large amount of distortions, can be successfully used in many areas, such as forest research, meteorology and surveying. This kind of image offers the advantage of providing spatially resolved information of all obstacles above the measurement point. Therefore it can be used as a tool for GNSS site satellite window diagram direct determining. In previous research authors have successfully tested terrain obstacles models obtained from terrestrial laser scanning and digital hemispherical photography (Nikon D90 12.3 megapixel digital semi-professional camera with Sigma 8mm f/3.5 EX DG circular fish-eye lens). Current study describes a method for rapid capturing the terrain obstacles by cheap and simple smartphones fisheye lens. Additionally authors describe method of smartphone camera levelling with the use of AHRS algorithm and development of centering method based on smartphone front camera image. Main aim of the research is to investigate the suitability of cheap fisheye lens for modeling terrain obstacles over the GNSS measurement points.