Abstract
This paper discusses the potential of current photogrammetric multi-head oblique cameras, such as UltraCam Osprey, to improve the efficiency of standard photogrammetric methods for surveying applications like inventory surveys and topographic mapping for public administrations or private customers. <br><br> In 2015, Terra Messflug (TM), a subsidiary of Vermessung AVT ZT GmbH (Imst, Austria), has flown a number of urban areas in Austria, Czech Republic and Hungary with an UltraCam Osprey Prime multi-head camera system from Vexcel Imaging. In collaboration with FBK Trento (Italy), the data acquired at Imst (a small town in Tyrol, Austria) were analysed and processed to extract precise 3D topographic information. The Imst block comprises 780 images and covers an area of approx. 4.5 km by 1.5 km. Ground truth data is provided in the form of 6 GCPs and several check points surveyed with RTK GNSS. Besides, 3D building data obtained by photogrammetric stereo plotting from a 5 cm nadir flight and a LiDAR point cloud with 10 to 20 measurements per m² are available as reference data or for comparison. The photogrammetric workflow, from flight planning to Dense Image Matching (DIM) and 3D building extraction, is described together with the achieved accuracy. For each step, the differences and innovation with respect to standard photogrammetric procedures based on nadir images are shown, including high overlaps, improved vertical accuracy, and visibility of areas masked in the standard vertical views. Finally the advantages of using oblique images for inventory surveys are demonstrated.
Highlights
In recent years, capturing and processing of oblique imagery has become a mature technology for 3D information extraction based on photogrammetric principles (Remondino and Gerke, 2015)
This paper discusses the potential of current photogrammetric multi-head oblique cameras, such as UltraCam Osprey, to improve the efficiency of standard photogrammetric methods for surveying applications like inventory surveys and topographic mapping for public administrations or private customers
Ground truth data is provided in the form of 6 ground control points (GCPs) and several check points surveyed with RTK GNSS
Summary
In recent years, capturing and processing of oblique imagery has become a mature technology for 3D information extraction based on photogrammetric principles (Remondino and Gerke, 2015). The most common design uses one photogrammetric nadir viewing camera combined with four tilted cameras with forward-, backward-, left- and right-viewing directions With respect to their spectral characteristics, the oblique sensor heads acquire the visible (RGB) bands. Given the increased number of oblique cameras on the market and the increased use of oblique imagery, software providers have updated the standard algorithms designed for vertical imagery, e.g. including oblique images in the aerial triangulation (AT). One important branch is cadastral surveying and topographic mapping for public administrations or private customers Such projects involved a nadir photo flight along with stereo plotting. By extending the photogrammetric process with oblique flights, the efficiency, and the market position, can be improved substantially Based on these considerations, TM has flown a number of urban areas in 2015 with an UltraCam Osprey Prime multi-head camera system from Vexcel Imaging. The differences and innovation compared to standard procedures based on nadir images are commented, paying attention to accuracy and to productivity aspects
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