Photogrammetric bridging of GPS outages in mobile mapping

A photogrammetric strategy for the orientation of image sequences acquired by Mobile Mapping Vehicles (MMV) is presented. The motivations for this are twofold: to allow image georeferencing in short GPS outages for a MMV under development at the University of Parma, currently without an IMU; to improve the consistency of image georeferencing between asynchronous frames. The method may also contribute to limit the drift errors of low-cost integrated IMU/GPS systems in GPS outages. Drawing on techniques developed for Structure and Motion (S&M) reconstruction from image sequences and accounting for the specific conditions of the MMV imaging geometry, highly reliable multi-image matches are found, refining image orientation with a final bundle adjustment. Dealing with scenes containing poor image texture, the automation of the convergence of the bundle to the solution is still a problem. After a successful orientation of an image sequences of ca 70 in, the accuracy of the orientation and reconstruction process was checked in a test field by means of GPS observations and check points. Although not all constraints between synchronous image pairs are yet enforced, the accuracy degradation along the sequence was found to be still well within the specifications for the MMV.