Integrated Bundle Adjustment with Variance Component Estimation – Fusion of Terrestrial Laser Scanner Data, Panoramic and Central Perspective Image Data

Terrestrial laser scanners and digital cameras can be considered largely complementary in their properties. Several instruments combine a laser scanner and a camera, with the laserscanner providing geometry information and the camera supplying point of surface colour. These approaches of data fusion make sub-optimal use of the complementary properties of the two devices, as they assign a master-and-slave casting to laser scanner and camera. A thorough exploitation of the complementary characteristics of both types of sensors should start in 3D object coordinate determination with both devices mutually strengthening each other. For this purpose a bundle adjustment for the combined processing of terrestrial laser scanner data and central perspective or panoramic image data, based on an appropriate geometric model for each sensor, was developed. Since different types of observations have to be adjusted simultaneously, adequate weights have to be assigned to the measurements in a suitable stochastic model. For this purpose, a variance component estimation procedure was implemented, which allows to use the appropriate characteristics of the measurement data (e.g. lateral precision of image data, reliability of laser scanner range measurement), in order to determine 3D coordinates of object points. Finding optimal weights for the different groups of measurements leads to an improvement of the accuracy of 3D-coordinate determination. In addition, the integrated scanner and camera data processing scheme allows for the optimal calibration of the involved measurement devices (scanner+camera self-calibration). Moreover, it is possible to assess on the accuracy potential of the involved measurements. The presented paper describes the basic geometric models as well as the combined bundle adjustment with variance component estimation. First results, based on data in a 360° test field, are presented and analysed. * Corresponding author.