Quality assessment for GPS-supported bundle block adjustment based on aerial digital frame imagery
Accuracy and reliability are two popular indicators for assessment of the quality of aerial triangulation. This paper explores these quality indicators in relation to GPS-supported bundle block adjustment based on aerial digital frame imagery with GPS navigation data. A set of aerial digital frame imagery, taken over hilly terrain using an SWDC-4 area-array digital camera made in China, was selected and used. These empirical images have superior resolution with a pixel size of 9 μm, with a ground sample distance of 10 cm and larger than traditional overlaps (80% longitudinal and 63% lateral). GPS-supported bundle block adjustment was carried out with the WuCAPS high-precision combined bundle block adjustment software package developed by the author. The achieved a posteriori standard deviation (rms errors of observation residuals) of the image coordinates is ±3·7 μm. The empirical accuracy of the photogrammetric point coordinates reaches ±7·1 cm for planimetry and ±4·8 cm for elevation on the ground, and the average redundancies (average components of the redundancy for one kind of observation) of the image coordinates and the camera station coordinates determined via GPS are more than 0·74 and 0·69, respectively. These results have shown that GPS-supported aerial triangulation with aerial digital frame imagery provides higher precision and reliability; the practical height accuracy is close to its theoretical possibility; also, it avoids the use of the cross strips and lines of ground height control points on each side of the adjusted block. This not only changes the present situation, in which height accuracy is always lower than the planimetric accuracy in aerial triangulation of aerial film images, but also opens up a new prospect in which the orientation points for models for stereoplotting need not be determined by full field surveying for topographic mapping of reasonably flat terrain at medium and large scales. Therefore, this paper provides an operational basis for a broad range of applications for aerial digital imagery in national basic surveying and mapping, and the rapid production and updating of geographic information in general.
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