Abstract
Abstract. This paper reports the results of an experiment that aims at the virtual reconstruction of a urban site that has been partially reshaped during the 20th century; the reconstruction process is based on period photos. The chosen case study is the eldest harbour of Palermo, named ‘Cala’; the site was bombed during World War II and new buildings took the place of the ruined ones. Two period photos, taken from an aircraft, document the buildings that were destroyed by bombs. The 3D restitution process used the ‘inverse’ projection from period photos (2D) to the virtual space (3D) ; the first step was therefore addressed to the calculation of the inner parameters (focal length, principal point coordinates) and of the cameras’ pose, i.e. their position and orientation. The data needed for these calculations were extracted from the 3D laser scanning survey of those buildings that appear in photos and that are still on site. The calculation of inner parameters and poses has been computed with a motion tracking commercial package. The second part of the paper focuses a process for the fruition of virtual reconstructions, based on the alignment of real panoramic images, generated by photos taken on site, and of virtual panoramic images, extracted from the 3D reconstruction model; the proposed method uses SfM photogrammetric tools.
Highlights
All along the 20th century the biggest towns in Europe were deeply transformed, by the reconstruction plans that followed war damages, or by urban renewal plans
The paper reports the results of an experiment aiming at the setup of a process for the 3D virtual reconstruction of no extant sites and buildings that are documented in period photos
Perspective restitution is the traditional approach to 3D monocular restitution; if some geometric features are known, the perspective restitution leads to the detection of the inner orientation parameters of the image and to the restitution of the size of segments in an unknown unit
Summary
All along the 20th century the biggest towns in Europe were deeply transformed, by the reconstruction plans that followed war damages, or by urban renewal plans (larger roads, more services, etc.). The geometric-based camera pose estimation demands 3D data of the environment that is displayed in the image, e.g. the coordinates of some relevant points (corners and the like); that is why the process is usually referred to as model-based tracking. If the inner orientation is known, one of the simplest solutions of the model-based tracking is provided by the Perspective-3-Point, usually reported as P3P. The PnP approach leads to a good camera pose estimation even when the depicted scene matches only partially the 3D model of the extant site. This property becomes relevant when the camera pose estimation process is addressed to period photos that show both extant and disappeared buildings. The matching of real and virtual panoramic images allows transitions between the two and supports the comprehension of the links between the present and the past features of the site
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