VBS RTK GPS-ASSISTED SELF-CALIBRATION BUNDLE ADJUSTMENT FOR AERIAL TRIANGULATION OF FIXED-WING UAS IMAGES FOR UPDATING TOPOGRAPHIC MAPS

Shih-Hong Chio

doi:10.1590/s1982-21702016000400038

Abstract

Unmanned Aircraft Systems (UASs) can collect high resolution and high quality images for local mapping. If the highly accurate GPS flying trajectory of a UAS is collected, it can support bundle adjustment aerial triangulation (AT) of UAS images and reduce the demands on ground control points (GCPs). This study installs a Trimble BD970 GNSS OEM on a fixed-wing UAS for capturing highly accurate GPS data by using a Virtual Base Station (VBS) RTK GPS technique for AT. Meanwhile, the GPS antenna-camera offset is resolved by stripwise linear drift parameters introduced in GPS observation equations, while performing bundle adjustment for AT. Additionally, self-calibration bundle adjustment is used in VBS RTK GPS-assisted AT to solve incomplete camera parameters calibrated by a close-range photogrammetric approach. The results show that the AT accuracy of fixed-wing UAS images collected with a 24 mm focal-length Canon EOS 5D Mark II camera at a flying height of 550 m above ground level is 0.21 m in planimetry and 0.22 m in height using two cross strips with two full GCPs at each corner of the block. The RMSE of check points from stereoscopic viewing can reach 0.27 m in planimetry and 0.24 m in height. The test results show that the accuracy of VBS RTK GPS-assisted bundle adjustment with self-calibration for the AT of fixed-wing UAS image can be used for updating local 1/5000 topographic maps in Taiwan.

Highlights

Unmanned aerial systems (UASs) are commonly used in military applications for reconnaissance, environmental observation, maritime surveillance, mine removal activities, etc
The test results imply the following conclusions: (1) This study confirms the feasibility of Virtual Base Station (VBS) RTK GPS-assisted self-calibration bundle adjustment for aerial triangulation (AT) of fixed-wing UAS images
(2) This study proves that incomplete camera calibration can be compensated for by self-calibration bundle adjustment AT

Summary

Introduction

Unmanned aerial systems (UASs) are commonly used in military applications for reconnaissance, environmental observation, maritime surveillance, mine removal activities, etc. They can be remotely controlled (e.g., flown by a pilot at a ground control station) or can fly autonomously (without pilots on board) by using pre-programmed flight plans (EISENBEISS, 2004). Because UASs can fly at low altitude and on cloudy days to collect high resolution and high quality images, UAS technology for low altitude photogrammetric mapping was developed (EISENBEISS, 2009). UASs are unsuitable for collecting images of large areas for mapping due to their small image formats, they are suitable for collecting high resolution UAS images for updating local topographic maps. Orthoimages (Bendea et al, 2007), topographic maps (Li, 2011) and digital elevation models (Haarbrink and Eisenbeiss, 2008) can be generated for mapping applications

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