Spatial measurement with consumer grade digital cameras
2008-10-30T16:55:35Z (GMT) by
This thesis develops the potential of consumer-grade digital cameras for accurate spatial measurement. These cameras are generally considered unstable but their uncertain geometry can be partially resolved by calibration. The validity of calibration data over time should be carefully assessed before subsequent photogrammetric measurement. The use of such digital cameras for photogrammetric measurement is increasingly accepted in many industrial fields but also in a diverse range of fields including medical and forensic science and architectural work. However, the stability of these cameras is less frequently reported in the literature, which can be attributed to the absence of standards for quantitative analyses of camera stability. The approach used to assess camera stability in this study is based on comparing the accuracy in the reconstructed object space, achieved using sets of interior orientation parameters of a sensor, derived in different calibration sessions. This technique was successfully applied to assess the temporal stability and manufacturing consistency of seven identical Nikon Coolpix 5400 digital cameras. These cameras demonstrated remarkable potential to maintain their internal geometry over a 1-year period. This study also identified residual systematic error surfaces, discernable in digital elevation models (DEMS) derived from image pairs. These ’domes’ are caused by slightly inaccurately estimated lens distortion parameters. A methodology that uses a mildly convergent image configuration removes the systematic error sources. This result is significant for DEM generation using low-cost digital cameras and a series of case studies demonstrated that this methodology can reduce the need for an accurate lens model and effectively increase the accuracy achievable with non-metric digital sensors.