ESACH Blog | The application of survey advanced techniques in Palazzo Ducale in Mantova, Italy

The European Heritage Tribune and ESACH believe it is important to share young people’s perspectives on cultural heritage. Therefore, the ESACH Blog features blog posts written by association members engaged in ESACH Talks. This blog post is written by Laura Cerliani and Annachiara Colombo, two of the speakers of the November 2020 Talk on New Technologies in Cultural Heritage.

The main objective of surveying in the architectural field is to lead to the knowledge of the object through the definition of an interpretative model of the artefact. In recent years, the application of survey advanced techniques has greatly extended the possibilities of understanding, investigating and rendering historic architecture and, in this regard, the work carried out on Palazzo Ducale in Mantova during the Survey Advanced Techniques class at Politecnico di Milano provides an exemplary contribution to the discussions about advanced technologies applied to built heritage surveying.

The object of the data recollection campaign, Palazzo Ducale, is an extensive architectural complex that stands in the higher part of Mantova, and which corresponded to the original nucleus of the ancient city. As the palace consists of numerous buildings, corridors, galleries, courts and gardens, the whole has developed as a microcosm that occupies an extended urban area and it has been defined as a palace in the form of a city.

In particular, the survey activity conducted along Professor Francesco Fassi aimed to use the 3D survey acquisition to elaborate the 2D metric data needed to define, at a later stage, the final preservation project of the Architecture Design and History Master Degree at Politecnico di Milano.

Static Terrestrial Laser Scanner

Range scanners are contactless instruments that emit laser light to take measurements: they receive and analyze the signal of the reflected radiation to sample the object in 3D coordinate points. Wide varieties of such scanners for digital acquisitions of 3D objects are available today and, in particular, the survey of Palazzo Ducale required Terrestrial Laser Scanners both in static and dynamic modes.

Figure 1: Palazzo Ducale, photo by Marco Introini. Source: Marco Introini, Luigi Spinelli, Architetture a Mantova. Da Palazzo Ducale alla Cartiera Burgo, Silvana Editoriale, Cinisello Balsamo, 2018

The main aim in applicating the Static Terrestrial Laser Scanner was the 3D acquisition of a small portion of the entire complex, corresponding to what is known as Palazzo del Capitano [Figure 1]. This instrument provides slow acquisitions characterized by high measurement accuracy and resolution. Before starting the Static Terrestrial Laser Scanner survey, it is important to set the parameters for the resolution of the acquisition according to the representation scale of the intended drawings.

After the data is recollected, the result is shown through the elaboration of a point cloud: being this a set of points defined in xyz coordinates that represents the outer surface of the object and that can be opened and visualized in AutoDesk ReCap (Reality Capture). The density of the point cloud expresses the resolution of the acquisition and, in this case, more than one hundred different scans acquired from different locations were required to obtain the final point cloud. To render the information in 2D metric, it is hereafter possible to import the point cloud in Autocad, which will be used to set the position of the section planes according to the drawings needed.

Figure 2: Longitudinal section – Point Cloud of Palazzo del Capitano in Autocad

The images [Figure 2, Figure 3] show the point cloud as imported in the software and the definition of the section plane. This served to obtain the longitudinal section of the Armeria, thus explaining in detail its characteristics and its relationship with the lower structures of Corte Vecchia.

Figure 3: Longitudinal section – Final result after the data elaboration

Terrestrial Laser Scanner Dynamic Mode

The Terrestrial Laser Scanner Dynamic Mode is a brand-new way to collect data: it opens the survey techniques to a more affordable panorama, and this especially in terms of instrument use. This mode permits to capture the morphology of a building and to define its point cloud by simply walking along the related space with the aid of a backpack on which the surveying tool is located.

The Dynamic Mode is a combination of mobile mapping with the range-based laser scanner survey. On one hand, it gives the possibility to map the survey path thanks to a self-geo-referred GPS system, while, on the other, the laser scanner is capable of building in real-time the point cloud.

Concretely, a laser scanner and a camera are installed on a backpack which, in our case, has been easily worn by both professor and students. The instrument was linked to a screen pad  through which we could visualize in real-time both the construction of the point cloud and our survey route. This latter surveying mode took approximately two hours, and, in this range of time, most of the open spaces and piazzas of Palazzo Ducale have been surveyed along with some of the inner rooms that are usually closed to the public.

Figure 4: Tridimensional view of the point cloud surveyed by the backpack, from Autodesk Recap

Referring to the Dynamic Laser Scanner, another aspect that needs to be considered during the survey phase is the walking speed of the surveyor as this affects both the resolution and the density of the point cloud that is being constructed. Therefore, the best expedient would be to repeat the gathering of the information a few times and with a low speed of walking, this in order to facilitate the scan recollection of the light reflections from all the surfaces that have been hit. 

The image [Figure 4] shows the final point cloud once imported in ReCap and, as for the static laser scanner, it is possible to use the model to rebuild plans, sections and other drawings [Figure 5].

Figure 5: Longitudinal section of the church of Santa Barbara and Giardino Pensile, by the point cloud

One of the defining elements of a Dynamic Survey resulted in the opportunity the tool gave to study the interrelationship of the Palazzo Ducale parts. In fact, we were surveying not a single room, but the entire complex, and, in this way, we were able to analyze how the pieces are put together as a coherent ensemble, untangling themselves among topography and landscape needs [Figure 6].

Figure 6: Longitudinal section of the church of Santa Barbara and Giardino Pensile, final result

Pros and cons of the two surveying techniques

After the analysis we think it would be proper to summarize the techniques through their comparison. At first, it has to be acknowledged that both of them are for the moment affordable only to a small range of experts, due to the money cost and also to the specific skills required.  Besides, and with regard to processing details, the static mode requires a time of data elaboration in-between the information acquisition and the drawing elaboration, that is not the case for the dynamic mode which is in fact what makes it more manageable. Nonetheless, both techniques can be considered as fundamental in the architectural and urban field even if they apply to different situations as they focus on different needs: by now the accuracy of the static one cannot be achieved by the dynamic one, whereas the latter allows a wider and more comprehensive survey to be made.

One of the biggest tasks for an architect approaching the intervention over the existing built environment is the preliminary analysis of the site. As very often there is no possibility to visit the place in person, practitioners are asked to collect information by internet sources, libraries and books. With this regard, the construction of an urban point cloud referred to historical and distinguished landmarks would be a first step towards the next frontier of informative mapping. In fact, by sharing this documentation, people would be allowed to better understand the characteristics of the place, to go in depth with research.

About the authors

Laura Cerliani is a Master Degree student at Politecnico di Milano, where she is attending the Master Degree in Architectural Design and History. The high interest in cultural heritage and preservation brought her to join ESACH and to go in depth with survey techniques and maintenance practices in historical sites.

Annachiara Colombo is a graduate student of Architecture Design and History at Politecnico di Milano. During her years of studies she went through different design approaches and she developed an interest in architecture as a creative practice that connects the city with the inhabitants. She is passionate about cultural heritage and the relationship between old and new in architecture.