Application of digital photogrammetry to complex topography for geomorphological research

This paper is concerned with the application of automated digital photogram metry, using 1:3000 scale photography to complex, natural landform surfaces , of typical interest to geomorphologists. It assesses the quality of the r esults obtained using a relatively cheap and readily available area based s tereomatching package, in terms of precision, accuracy and external reliabi lity. Precision is investigated with reference to the confidence that can b e placed in individual matches. Accuracy is evaluated using specially colle cted, independent datasets obtained from an area of complex topography in G len Affric, Scotland. Data collection was stratified to areas of different surface roughness. External reliability is judged with respect to estimates of slope, a key parameter in geomorphological investigations. The results show that, whilst the effects of grid density and vegetation correction are the most important controls upon the accuracy and the external reliability of the photogrammetric results, collection parameters associated with the stereomatching process can also exert some control, particularly in areas o f complex topography. It is impossible to generalize rules for choice of op timal collection parameters without careful consideration of the surface un der investigation. Given that maximum grid densities are defined by the obj ect space pixel resolution, the paper concludes that surface quality is lar gely governed by traditional controls upon photogrammetric data quality (ca mera calibration, base:distance ratio, ground control), combined with eithe r scanning density or digital image resolution. However, over some surfaces , careful consideration has to be given to the effect of matching parameter s.