Fisheye Multi-Camera System Calibration for Surveying Narrow and Complex Architectures

Abstract

Narrow spaces and passages are not a rare encounter in cultural heritage, the shape and extension of those areas place a serious challenge on any techniques one may choose to survey their 3D geometry. Especially on techniques that make use of stationary instrumentation like terrestrial laser scanning. The ratio between space extension and cross section width of many corridors and staircases can easily lead to distortions/drift of the 3D reconstruction because of the problem of propagation of uncertainty. This paper investigates the use of fisheye photogrammetry to produce the 3D reconstruction of such spaces and presents some tests to contain the degree of freedom of the photogrammetric network, thereby containing the drift of long data set as well. The idea is that of employing a multi-camera system composed of several fisheye cameras and to implement distances and relative orientation constraints, as well as the pre-calibration of the internal parameters for each camera, within the bundle adjustment. For the beginning of this investigation, we used the NCTech iSTAR panoramic camera as a rigid multi-camera system. The case study of the Amedeo Spire of the Milan Cathedral, that encloses a spiral staircase, is the stage for all the tests. Comparisons have been made between the results obtained with the multi-camera configuration, the auto-stitched equirectangular images and a data set obtained with a monocular fisheye configuration using a full frame DSLR. Results show improved accuracy, down to millimetres, using a rigidly constrained multi-camera.

Procedures for Condition Mapping Using 360° Images

“…Most applications of 3D photogrammetry are based on central perspective (also referred to as "frame" or "pinhole") cameras, notwithstanding, fisheye lenses are also becoming very popular for metric reconstructions for their larger FoV [17]. It is not the authors' intention to review here the basic principles of photogrammetry, as several handbooks are available in the technical literature (see, for example, the work of [18]).…”

Tower of Belém (Lisbon)–Status Quo 3D Documentation and Material Origin Determination

“…Data acquisition in these environments is complex due to the limited space for taking photographs, and for the distribution of control and check points. Other authors have used photographic systems at a higher cost than the used in this work, which provide greater agility in data collection, [47]. In this project, this element of the Tower has been photoreconstructed and georeferenced with low cost means (Sony α330 camera).…”

“…A fisheye lens was not available as recommended [47,48], so work had to be done with the available 18 mm lens. The door connections on each floor were also surveyed, including the entrance to each room in order to facilitate the posterior registration with the point clouds of the interior rooms obtained by the TLS.…”

“…The width of each door was measured "in situ" on the base of the arch in order to scale the cloud and facilitate the alignment with the main cloud obtained by TLS. The registration of the partial clouds and the final A fisheye lens was not available as recommended [47,48], so work had to be done with the available 18 mm lens.…”

A Fusion-Based Workflow for Turning Slam Point Clouds and Fisheye Data Into Texture-Enhanced 3d Models

“…In general terms, the photogrammetric processing of these kind of images presents several issues, especially if the aim is to achieve an accurate metrical reconstruction of the surveyed object (Barazzetti, Previtali, & Roncoroni, 2017;Perfetti, Polari, & Fassi, 2018). Several problems must be considered, and different topic must be deepened.…”