The Example of using action cameras in the invention of perforated objects - a case study in the Royal Castle

The article explores the possibility of low-cost action camera usage in inventory of hard-to-reach objects with complex structure. The main focus of the study is to compare data and results acquired from action camera, full-frame camera and terrestrial laser scanning. The object of the study was timber-earth embarkment exhibited in Royal Castle in Warsaw. It is characterised by perforated surface with high reflectivity, as well as cracks and hard to reach spaces. The study employs the Xiaomi Mi 4K Action Camera, Canon EOS 5D Mark II and Leica RTC 360 for comparison to TLS. The measurement consisted of few stages: setting of control points and light sources, gathering two sets of photos: general images acquired by full-frame camera and precise images gathered by full-frame camera and action camera. The elaboration of the data was mainly done in Agisoft Metashape, with some additional work in GIMP image editor and CloudCompare used for analysis. Results show that, despite high level of usage in case of texture, images from action camera are very demanding if we want to get satisfying geometry of the resulting model. Illumination and stabilisation of the camera are crucial in this process. In conclusion, the article emphasises high value of data acquired from action camera, but also highlights important conditions that have to be met for the data to be usable.