Direct exterior orientation determination in close-range photogrammetry for cultural heritage recording

In this thesis a low-cost approach for cultural heritage recording is developed. The necessity for comprehensive and accurate heritage recording derives from the constant threat of heritage being damaged or destroyed. Close-range photogrammetry utilising consumer-grade digital cameras has proven efficient in this area. Recognising the desirability to record data in a three-dimensional national coordinate system conventionally requires establishing coordinated target points for exterior orientation determination. This is time consuming, costly and can be objectionable on sensitive sites. In this study this problem was overcome by developing an image-based recording system that is capable of direct exterior orientation determination. The system comprises a consumer-grade digital camera, a small-size and low-cost orientation sensor, and a differential Global Positioning System (DGPS) receiver. The focus on low-cost and easy-to-use components enables utilisation by non-specialists for heritage recording. In this research project methods for rotational and positional offset calibration between system components were devised and the practicability of the recording system was tested at Loughborough University and in case studies at two real heritage sites. Testing involved assessing offset calibration precision and stability as well as achievable absolute and relative accuracy. The results of these tests demonstrated that with sufficiently consistent calibration values, data for medium accuracy measurements (40 mm absolute and 12 mm relative accuracy) can be recorded without using any control. This thesis also explores methods for enhancing usage and accessibility of data representing cultural heritage. It was demonstrated that storing image and corresponding exterior orientation information in a single file and visualising heritage data in Google Earth can provide several benefits for cultural heritage recording and conservation projects.