3D reconstruction with fisheye images strategies to survey complex heritage buildings

Over the last few decades photogrammetry and laser scanning have been frequently considered valuable tools for creating three-dimensional models from which metric and radiometric information can be derived for the survey of cultural heritage buildings, reverse engineering, space exploration and other areas. However reconstructing old heritage buildings digitally may be a challenging task especially when the shape, geometry and volume of these buildings are intrinsically complex therefore requiring specific methods or ad-hoc solutions. Medieval castles are typical constructions that exhibit these kinds of features with inaccessible locations, bridges, wide areas followed by small and limited spaces, battlements, towers and walls occluded by vegetation. This variety of problems can prolong the time required to complete the tasks when using laser scanning or photogrammetry with conventional lenses. In this paper we present a research of use of fisheye lenses in photogrammetry, for capturing medieval castles´ geometric and radiometric information of hard to reach places. We conclude that this reduces the total time needed to capture the same amount of information gathered with other instruments, it allows replacing the usage of Unmanned Aerial Vehicles (UAV) in low flight situations, makes the survey connection between areas of a building easier, reduces the total number of images and allows making a general fast survey. The castles illustrated in this paper are the Castle of Sesimbra and the Castle of The Convent of Christ, both in Portugal.