Aerial photogrammetry procedure optimized for micro uav

The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XL-5, 2014 ISPRS Technical Commission V Symposium, 23 – 25 June 2014, Riva del Garda, Italy AERIAL PHOTOGRAMMETRY PROCEDURE OPTIMIZED FOR MICRO UAV T. Anai a, *, T. Sasakia, H. Otanib, K. Osaragia, N. Kochia a b General Technology Div., R&D Dept., TOPCON CORPORATION, 75-1, Hasunuma, Itabashi, Tokyo - Smart Infrastructure Company, Technology Development Dept., TOPCON CORPORATION, 75-1, Hasunuma, Itabashi, Tokyo Commission V, ICWG1/5b KEY WORDS: Photogrammetry, UAV, Tracking, Bundle adjustment, DSM, Robust ABSTRACT: This paper proposes the automatic aerial photogrammetry procedure optimized for Micro UAV that has ability of autonomous flight. The most important goal of our proposed method is the reducing the processing cost for fully automatic reconstruction of DSM from a large amount of image obtained from Micro UAV. For this goal, we have developed automatic corresponding point generation procedure using feature point tracking algorithm considering position and attitude information, which obtained from onboard GPS-IMU integrated on Micro UAV. In addition, we have developed the automatic exterior orientation and registration procedure from the automatic generated corresponding points on each image and position and attitude information from Micro UAV. Moreover, in order to reconstruct precise DSM, we have developed the area base matching process which considering edge information. In this paper, we describe processing flow of our automatic aerial photogrammetry. Moreover, the accuracy assessment is also described. Furthermore, some application of automatic reconstruction of DSM will be desired. 1. INTRODUCTION Nowadays, due to the diffusion of low-cost GPS-IMU and also the progress of control technique of Micro UAV in past several years, the Low-cost Micro UAV system has been widely used as the useful platform in the application field of aerial photogrammetry such as agriculture, archaeology, traffic monitoring, and disaster area surveying (Remondino, 2011). The important ability of Micro UAV is the autonomous flight along previously planned waypoint. From this ability, fully automatic image data acquisition using digital still camera mounted on Micro UAV has becomes possible. Accordingly, a large amount of image data can be obtained for creating of precise orthophoto and Digital Surface Model (DSM) of object area. Additionally, the processing of aerial triangulation using a large amount of image data has to be performed automatically. The Structure from Motion (SfM) has been widely used as an efficient technique of 3D reconstruction from numerous image data. The modern SfM consists of efficient feature point description for automatic detection of corresponding points and bundle adjustment for numerous image data. The breakthrough of efficient feature point description has been given by SIFT and its improvement (Lowe, 2004). The good implementations of bundle adjustment using numerous image data have been given as Sparse Bundle Adjustment (SBA) and its improvement (Lourakis, 2009). Therefore, many applications of photogrammetry using Micro UAV have achieved fully automatic processing by using SfM approach. Nevertheless, the processing cost of feature point detection and matching and also bundle adjustment is still important problem. Moreover, if the information of global coordinate is not given, the results of SfM are obtained in model space that has arbitrary position, scale and rotation. Another important problem is that estimated parameters generally include the accumulative error based on feature point matching results. In order to resolve these problems, utilization of information from on-board GPS-IMU is one solution. In the case of standard application of automatic aerial triangulation, direct geo-referencing approach using GPS and IMU on UAV is often considered. However, GPS-IMU integrated on low-cost Micro UAV has not enough accuracy because GPS unit on Micro UAV only has ability of single positioning from limitation of cost. Thus, exterior orientation of SfM using Micro UAV has to consider ground control points (GCP) and GPS-IMU information simultaneously. For these problems mentioned above, we have been concentrating to investigate the Structure from Motion (SfM) technique using GPS in recent years (Anai et al., 2010). In these investigations, we have proposed the robust feature point tracking method based on the “Orientation Code” (OC) image processing (Ullah, 2001, Takauji 2005). Also, bundle adjustment method for video image that uses both SfM technique and GPS data with considering error in GPS observation. Additionally, the application for Micro UAV using these techniques has been reported (Anai et al., 2012). In this paper, we describe about improvements of our method, which include robust image matching supported by low accuracy GPS-IMU information and automatic exterior orientation process. On the other hand, In order to create precise DSM robustly, we propose extended Edge TIN-LSM method which integrates edges and which is able to cope with differences in right and left image shape, brightness changes and occlusions (Kochi et al., 2012). * Corresponding author. This is useful to know for communication with the appropriate person in cases with more than one author. This contribution has been peer-reviewed. doi:10.5194/isprsarchives-XL-5-41-2014 41 The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XL-5, 2014 ISPRS Technical Commission V Symposium, 23 – 25 June 2014, Riva del Garda, Italy This paper is structured as follows. Section 2 describes our processing flow of exterior orientation procedure. Section 3 describes processing flow of creating DSM using proposed TIN-LSM Method. Moreover, accuracy assessments for some application test are described in Section4. The conclusion about our proposed method is described in Section 5. 2. AERIAL PHOTOGRAMMETRY PROCEDURE FOR LOW-COST MICRO UAV This section describes about processing flow of our proposed aerial photogrammetry procedure. The most important problem of aerial photogrammetry using low-cost Micro UAV is low accuracy of GPS-IMU. The GPS-IMU of low-cost Micro UAV is enough for the navigation of Micro UAV in local area. However, the observation of GPS only has single positioning mode and the time synchronization between still image and GPS-IMU is incomplete. Furthermore, the accuracy information of GPS-IMU is not provided correctly. From these backgrounds, the proposed method is performed as shown in Figure 1. At the first, in order to obtain the dense corresponding pass points between each still image, feature point tracking process using common feature points is performed by the OC Image Processing supported by GPS-IMU information. As the next step, generation of tie point between each stereo model and flight line is performed us (...truncated)