CHANGING THE PRODUCTION PIPELINE – USE OF OBLIQUE AERIAL CAMERAS FOR MAPPING PURPOSES

Abstract

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. 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.

Use of Vertical Aerial Images for Semi-Oblique Mapping

“…The software functionality includes data visualization (simultaneous co-located visualization of nadir and oblique images, image selection, view rotation, navigation pane) and mapping (point measurement in monoplotting and multi-image mode, 3D vector import, editing and export, layer management). The investigations on Imst test site (Austria) in 2015 and Bergamo (Italy) in 2016 confirmed earlier findings that the inclusion of oblique images to the nadir image block improves the accuracy of the aerial triangulation mainly in the vertical (Rupnik et al, 2015(Rupnik et al, , 2014 and, thanks to the additional viewing directions, allows to generate dense 3D point clouds to reconstruct buildings façades or other features generally not visible in the nadir views (Moe et al, 2016). Beside the investigations on oblique aerial cameras, AVT focused on the possibility to exploit the lateral parts of nadir images ("semi-oblique"), where, due to the perspective geometry, building façades or other vertical objects are visible by an oblique viewing direction.…”

“…The GEOBLY software, originally designed for Maltese-cross cameras (Moe et al 2016), was extended to the semi-oblique scenario of nadir-looking aerial cameras. In this mode, the outer parts of the images (according to a percentage threshold that can be freely chosen by the user) are cropped, and the corresponding oblique viewing directions (forward, backward, right or left) are assigned automatically.…”

“…The Austrian company Vermessung AVT-ZT-GmbH (later AVT) with subsidiary Terra Messflug GmbH has been operating oblique aerial flights with UltraCam Osprey cameras for cartographic mapping since 2015. After rigorous investigations on the geometric properties of the oblique cameras and their potentials for mapping applications, AVT, in cooperation with the research institute Bruno Kessler Foundation (FBK) in Trento (Italy), has implemented the GEOBLY software for inventory survey and topographic mapping using oblique imagery (Moe et al, 2016). The software functionality includes data visualization (simultaneous co-located visualization of nadir and oblique images, image selection, view rotation, navigation pane) and mapping (point measurement in monoplotting and multi-image mode, 3D vector import, editing and export, layer management).…”

Oblique Photogrammetry Supporting 3d Urban Reconstruction of Complex Scenarios

“…The use of oblique multi-head camera systems can potentially tackle the problem and provide for an efficient means of information extraction in urban scenarios. Many research works already proved the potential of oblique photogrammetry in dealing with information extraction in such contexts (Haala and Rothermel, 2015;Frommholz et al, 2015;Moe et al, 2016). However, although façade reconstruction is feasible through recently improved multi-view image matching and meshing techniques, the reconstruction of highly detailed and accurate 3D objects in complex and historical urban environments still presumes additional data captured from terrestrial viewpoints.…”

“…Further details are listed in Table 1. The Aerial Triangulation (AT) is performed following the strategy presented in (Moe et al, 2016). The AT results of the nadir images are extended to include, by means of an in-house developed tool, the four additional oblique views with their calibrated relative orientation parameters (offsets, angles).…”