Proceedings International Workshop on Mobile Mapping Technology

li, rongxing

Bibliographic data

Monograph

Persistent identifier:: 856671290

Author:: Li, Rongxing

Title:: Proceedings International Workshop on Mobile Mapping Technology

Sub title:: April 21 - 23, 1999, Bangkok, Thailand

Scope:: 1 Online-Ressource (Getr. Zählung [ca. 400 Seiten])

Year of publication:: 1999

Place of publication:: London

Publisher of the original:: RICS Books

Identifier (digital):: 856671290

Illustration:: Illustrationen, Diagramme, Karten

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Monograph

Collection:: Earth sciences

Chapter

Title:: [Session 4: Sensor Integration and Calibration]

Document type:: Monograph

Structure type:: Chapter

Chapter

Title:: The Calibration of Imaging Sensors Integrated into a Rapid Route Mapping System. C. S. Fraser, A. M. Judd.

Document type:: Monograph

Structure type:: Chapter

4-1-2 1 INTRODUCTION Bushfires represent a significant natural disaster threat throughout much of Australia, and thus bushfire mitigation is a high priority for power utilities, both in regard to minimising fire damage to transmission line infrastructure and ensuring that the threat of the fire from vegetation overhanging high voltage transmission lines is minimized. The latter is achieved partially through ensuring adequate clearance between powerlines and adjacent vegetation, especially fire prone eucalyptus trees. Given the 1000s of kilometers of power lines crisscrossing the Australian landscape, the ongoing task of monitoring vegetation clearance is very significant. Indeed, in the context of asset management, not only clearance dimensions need to be recorded, but also the spatial locations of the power poles and the associated attributes (e.g. information regarding the insulators, presence of transformers, number of cross-arms, etc.). The recording of all these features can be achieved using the technology of mobile mapping. The Rapid Centreline and Attribute Mapping System (RCAMS) is a vehicle, railcar or aircraft borne rapid mapping system developed to enable the recording of positional and attribute data, using the integrated technologies of GPS satellite positioning, inertial positioning sensors and stereo video imagery (Leahy & Judd, 1998). The principal applications of RCAMS have to date been road centreline mapping (including the recording of roadside attributes such as signage) and powerline mapping. RCAMS has been successfully employed to provide in-car navigation data for major cities in Australia, and it has been used to record more than 2000km of high-voltage powerlines in the State of Victoria. As is indicated in Figure 1, the vehicle mounted configuration of RCAMS, while utilizing multi-camera video imagery, has not thus far employed stereo imagery since road attribute data is referenced only by the adjacent position on the road centreline. Stereo imagery has, however, been employed as a component of an RCAMS configuration utilised for high-precision, rapid rail mapping where rail corridor features are recorded to an accuracy of 0.3m (Hunt et al, 1998). With airborne RCAMS, stereo imagery plays a central role in feature positioning and in the present paper the discussion will be confined to this configuration. Put simply, in the application of airborne RCAMS to powerline and vegetation mapping, the position of any ground feature can be determined by spatial intersection from the stereo-video imagery, with the geo-referencing of this position being provided by the Exterior Orientation (EO) of the dual-camera system. The positional component of the EO is provided by GPS, whereas the orientation component is determined using both multi-antenna GPS and inertial navigation sensors. In order for both power pole positions and vegetation clearance to be determined to the required accuracy, nominally the lm level, it is important that a comprehensive sensor calibration and EO determination be performed for the dual-camera video system. This photogrammetric aspect of RCAMS forms the subject of the present paper. Following a brief overview of RCAMS, and a description of the video-based positioning component, the approach adopted for camera system self-calibration and EO is described. The results of an experimental field calibration are also presented and conclusions are drawn regarding the field calibration procedure and the merits of employing a mobile mapping approach for powerline vegetation mapping to support bushfire mitigation. 2 BRIEF OVERVIEW OF RCAMS Figure 2 illustrates a schematic of the airborne RCAMS configuration. Aircraft position is recorded via an Ashtech 3DF GPS system, which incorporates four GPS antennas, a ‘reference’ antenna over the centre of the fuselage, an antenna on each wing tip and one on the tail. Orientation (roll, pitch and yaw) of the aerial platform is provided by the 3DF system, with pitch and roll rate gyros providing supplementary orientation data. Kalman filtering provides the fundamental computational model for integrating the positional and orientation data, as described in detail by Leahy and Judd (1998; 1999). Not shown in the schematic of Figure 2, but necessary for the kinematic positioning of RCAMS, is a GPS reference station in the vicinity of the project area. RCAMS incorporates video recorders for three video imaging cameras, a wing tip mounted, forward-looking stereo configuration, the calibration of which forms the main topic of this paper, and a camera aimed vertically downwards. In the powerline mapping project discussed, experimental application of a scanning infra-red CCD imager was also attempted. This met with limited success, however, due to the characteristics of the particular IR imager used. As a consequence, the vertical imaging capability of RCAMS will not be further discussed in the present paper. The two stereo cameras comprised Pulnix CCD sensors (pixel array size of 750 x 580 and format of 6.4 mm x 4.8 mm) with lenses of 17 mm focal length. Mounted with a photogrammetric base of 10.4 m, the cameras were mildly convergent so as to produce nominally 100% overlapping images when tilted downwards at a depression angle of 35° from the horizontal, and when flown at a low-level ground clearance of 50m. The resulting average camera-to-object distance of 80m yielded an image scale of 1:4700. As will be mentioned, digital stereo image pairs where extracted from the SVHS video tape at about 20m intervals, which provided an along-track image overlap of 60%. 3 CAMERA SELF-CALIBRATION AND EO 3.1 Network Configuration For practical reasons it was decided to adopt a system calibration approach in the determination of photogrammetric parameters for the airborne RCAMS. In order to geo-reference features identified in the stereo imagery, the following are required:

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