Direct exterior orientation determination for a low-cost heritage recording system

Close range photogrammetry has proved effective as a cost-effective and easy-to-use method for cultural heritage recording. Off-the-shelf digital cameras can be used to rapidly acquire data at low cost, allowing non-experts to become more involved in their local heritage, an important aspiration identified in this collaboration between English Heritage and Loughborough University. To achieve this while also allowing for measurements in a 3D national reference system, a recording system has been developed that is capable of deriving the exterior orientation during exposure directly and cheaply. The system comprises a digital camera, a small 3D orientation sensor and a GNSS antenna, assembled in a frame that allows calibration of the offsets between the components. Testfield data was used to investigate calibration precision and stability as well as achievable absolute and relative accuracy. The results of data analysis indicate that the system can meet the accuracy requirements for medium accuracy heritage recording, even with slightly unstable offset calibration values.