New developments in Multimedia Photogrammetry

Applications of photogrammetry, where the beam from an object to the sensor passes several optical media with different refractive indices, are called multimedia photogrammetry. This presentation describes a fast and versatile algorithm for the strict geometric modelling in multimedia photogrammetry, which can easily be implemented as a module into spatial resections, intersections or bundle solutions. The solution is restricted to the standard case of multimedia photogrammetry, where the object is situated in a liquid, the sensor is positioned in air, and a plane-parallel glass plate divides these two media. In combination with the choice of a suitable local coordinate system, this environment can be modelled very efficiently and the computational effort connected with the twice-broken beam can be reduced significantly. A further strong reduction of the computational effort has been achieved by downloading the geometric effects of the multimedia environment into a two-dimensional lookup-table and thus avoiding time consuming iterative solutions. Integrated into a bundle adjustment program with self calibration, the refractive index of the liquid (or even of the refractive indices of the liquid and the glass plate) can also be introduced as an unknown and determined simultaneously. In practical tests the refractive index of a medium could be determined with a standard deviation of 0.15 /00, which is better than the accuracy of most commercial refractometers.