Geometric consistency and stability of consumer-grade digital cameras for accurate spatial measurement

This is a journal article. It was published in the journal, The Photogrammetric Record [© Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd] and the definitive version is available at: http://www3.interscience.wiley.com/journal/118539355/homeIt is known that uncertain internal geometry of consumer-grade digital cameras limits the accuracy of data that can be extracted. These cameras can be calibrated, but the validity of calibration data over a period of time should be carefully assessed before subsequent photogrammetric measurement. This paper examines the geometric stability and manufacturing consistency of a typical low-cost digital camera (Nikon Coolpix 5400) by estimating the degree of similarity between interior orientation parameters (IOP), established over a oneyear period. Digital elevation models (DEMs) are extracted with differing interior orientation parameters (IOP) sets and accuracies are compared using data obtained from seven identical cameras. An independent self-calibrating bundle adjustment (GAP) and the Leica Photogrammetry Suite (LPS) software were used to provide these datasets. Results are presented that indicate the potential of these cameras to maintain their internal geometry in terms of temporal stability and manufacturing consistency. This study also identifies residual systematic error surfaces or “domes”, discernible in “DEMs of difference”. These are caused by slightly inaccurately estimated lens distortion parameters, which effectively constrain the accuracies achievable with this class of sensor

Structure-From-Motion Photogrammetry to Support the Assessment of Collapse Risk in Alpine Glaciers

The application of Structure-from-Motion (SfM) Photogrammetry with ground-based and UAV camera stations may be exploited for modelling the topographic surface of Alpine glaciers. Multi-temporal repeated surveys lead to geometric models that may be applied to analyze the glacier retreat under global warming conditions. Thanks to the integration of point clouds obtained from ground-based and UAV imaging platforms, a complete 3D reconstruction also including vertical and sub-vertical surfaces may be achieved. These 3D models may be also exploited to understand the precursory signals of local collapse that might represent a risk for tourists and hikers visiting glaciers. In this paper a review on the application of SfM Photogrammetry in the field of glaciological studies is reported. The case of Forni Glacier in the Italian Alps is presented as emblematic study. Photogrammetric data sets obtained from measurement campaigns carried out in 2014, 2016, 2017 and 2018 have been processed using a common workflow. Attention is paid to a few crucial aspects, such as image orientation and calibration, dense surface matching, georeferencing and data fusion. In the end, the use of output point clouds to evaluate the risk of collapse in the Forni Glacier is addressed