DBPapers
DOI: 10.5593/SGEM2014/B23/S10.019

DIGITAL AEROTRIANGULATION WITH VERTICAL DATUM SCALE MODIFICATION RESPECTS NATIONAL HORIZONTAL COORDINATE SYSTEM

Z. Svec, M. Faltynova, K. Pavelka
Wednesday 1 October 2014 by Libadmin2014

References: 14th International Multidisciplinary Scientific GeoConference SGEM 2014, www.sgem.org, SGEM2014 Conference Proceedings, ISBN 978-619-7105-12-4 / ISSN 1314-2704, June 19-25, 2014, Book 2, Vol. 3, 153-160 pp

ABSTRACT
The Geometric quality of a photogrammetric product is given mainly by the accuracy of the determination of the sensor orientation. There are several ways how to determine the exterior orientation parameters of aerial frame cameras. In the past, the most frequent option was the aerotriangulation with the bundle block adjustment based on tie and ground control points. At the begining of the 21st century there was a mass commencement exercitation of the on-the-board GNSS and IMU devices and a few new possibilities have emerged. However, the simplest solution comprises direct georeferencing from GNSS/IMU data but many experiments have confirmed that superior results are given by integrated sensor orientation. It means digital aerotriangulation with the GNSS/IMU orientations as the observations. Observations of several ground control points are proposed to eliminate systematic errors and to assure absolute accuracy of the whole block. The GNSS positioning refers to the 3D rectangular earth-centred coordinates in the WGS84 coordinate system. However, the results of the block aerotriangulation are, due to the cartographical demands, mostly required in the national vertical and horizontal reference system. Therefore, GNSS/IMU data has to be transformed to the desirable coordinate systems before the integration to adjustment. Nevertheless, computations in the national coordinate system cause a few problems because the geometric model of block adjustment operate within cartesian coordinate system with the identical scale of each axis. As all the modern national horizontal coordinate systems are conforming with some scale error, the condition of the identical scale is not acomplished. Furthermore, if the gravity-related vertical datum is used, not even the condition of orthogonality is fulfilled. While non-orthogonality has practically no impact, different scale of positioning coordinate system seriously affects altitudes of image projection centers and causese biases in the block adjustment. There are two ways how to avoid this effect. The first one is based on the camera focal length modification and the second one on changing the vertical coordinate system scale. Unfortunatelly, none of these exact methods are commonly not been used in practice. The article looks at modification of altitudes of aerial photograph projection centers before integrated sensor orientation. Numerous outcomes affirming the theory are performed.

Keywords: Integrated sensor orientation, Aerotriangulation, Direct georeferencing, Datum problem, Scale error