Reconstructing the Ducal Palace of Sora with Hyperspaces

Humans curious like us have at least once wondered: how did my town use to appear before the grandparents of my grandparents were even born? Until very recently, to answer this question, we could only hope to be able to find pictures, paintings and documents that could testify this past in the historical archives of the town. Today, however, we have 3D technologies and above all we have Augmented Reality. These technologies can indeed be used as tools to recover and enhance our historical memory.

Thanks to the Hyperspaces platform by Inglobe Technologies, Arch. Giuseppe Accettola and Eng. Paolo Accettola, two esteemed colleagues of ours, have employed Augmented Reality to provide a unique valorization experience: to give new life to a piece of the city that today, unfortunately, no longer exists because of a terrible earthquake. Specifically, to commemorate the centenary of the Marsica earthquake of 1915, the two authors wanted to revive the Ducal Palace, a majestic building which is no longer visible.

The ducal Palace

The palace was built probably by Della Rovere family in 1500 and later belonged to the Boncompagni and the Annonj. It was depicted in various works of art and a design by Architect Vespignani of 1831, now preserved in the Sir John Soane’s Museum in London, allows us to reconstruct part of the architecture. The Palace was structured over three floors with a tower incorporated into the building. In close connection with the building and with the Roman bridge over the Liri river , in 1723, the Court Gate was erected by the Duke Antonio Boncompagni as a monumental entrance to the city, by reusing the material taken from the ancient temple of Serapis. The Court Gate, was demolished in the mid-nineteenth century along with the Roman bridge, whereas the Ducal Palace, badly damaged by the 1915 earthquake, was later dismantled during the subsequent reconstruction of the city. In its place there is now a modern building overlooking Corso Volsci, the main artery of the historical center of the city; it somehow recalls the lines of the ancient palace.

Creation of an AR experience with Hyperspaces platform

The Augmented Reality experience consists of a contextual access and view of the Ducal Palace on a mobile device as it appeared at the end of 1800. As  it is already well known, Hyperspaces platform offers the opportunity to create pathways to improve touristic experience where each geolocated node of the path can be associated with digital contents of different types: text, images, audio-video and 3D reconstructions. For this purpose, the authors have devised a path that contains, for the moment, just one node, i.e. the Ducal Palace, with a wealth of information related to documents and historical images, the current situation, and the 3D model of the building at the end of 1800. This node is accessed through three different modes: Keyword Search in the cloud, QR code and GPS location near the building.

Fig. 1: The building at the end of 1800 and the existing building.

Method of detection and tracking used in the experience

The Hyperspaces platform features a powerful method of 3D recognition and tracking that is employed to superimpose the 3D model of the original palace onto the current one. The latter was used as a reference target with its surroundings represented by the riverfront and by adjacent buildings. This method consists in defining a target through a set of photos of the object to be recognized, and a mesh of the same which object is then used to properly align the pattern of the original palace with the current one.

3D model of the Ducal Palace and the mesh of the existing building

The 3D model of the old building of the Ducal Palace used for the AR experience was obtained by state of the art 3D modeling software (3DStudio Max and SketchUp) starting from documents and images of the time. In order to reconstruct the 3D mesh of the existing building later used for tracking, a 3D photogrammetric reconstruction software has been used by relying on images taken from different angles (Autodesk 123D Catch). Fig. 2 illustrates the two models.

Fig. 2: The 3D models of the old and the present building.

Creation of the reference target

In order to create the reference target, about 30 pictures were taken in the surrounding of the area of the AR experience. This area is located on the left side of the river Liri near the Naples bridge, at optimal distance from the building which is located on the opposite side of the watercourse. The photos were taken in order to obtain a set of congruent images with different angles and positions in the neighborhood of point of view.

Association between 2D and 3D points for tracking

The Hyperspaces platform offers a powerful algorithm for real-time 3D object tracking. This method has been employed  to visualize the 3D model of the Ducal Palace overlaid on the existing building. With this semi-automatic tool you can easily identify associations between 3D objects and 2D objects (fig. 3), once the 3D model of the old building has been properly aligned and superimposed on the mesh of the current building.

Fig. 3: Association between 2D and 3D points for tracking.

Final result

Once all the data are loaded on the platform, the correct view of the data was tested via web, as well as the quality of the augmentation and the rendering of digital content in AR mode. Finally, also the impact of sunlight has been checked. The quality of the augmentation has proved to be very good and the influence of light has little impact on the quality of the experience, even if these factors are susceptible of further improvements achievable simply by replicating the setup with a larger number of points of observation and photo.  Also the visualization of the 3D model of the Palazzo Ducale, despite the simplicity of the textures, has given good results. The image in fig. 4 shows the final result of the AR experience, with the view of the old building of the Ducal Palace superimposed onto the current building, as shown on the screen of an iPad and the corresponding screenshot.

Fig. 4: The AR experience from iPad.

This post is also available in: Italian