Scan-to-HBIM-to-VR: An Integrated Approach for the Documentation of an Industrial Archaeology Building

: In this paper, we propose a comprehensive and optimised workﬂow for the documentation and the future maintenance and management of a historical building, integrating the state of the art of different techniques, in the challenging context of industrial archaeology. This approach has been applied to the hydraulic work of the “Sostegno del Battiferro” in Bologna, Italy, an example of built industrial heritage whose construction began in 1439 and remains in active use nowadays to control the Navile canal water ﬂow rate. The initial step was the deﬁnition of a 3D topographic frame, including geodetic measurements, which served as a reference for the complete 3D survey integrating Terrestrial Laser Scanning (TLS), Structured Light Projection scanning, and the photogrammetric processing of Unmanned Aircraft System (UAS) imagery through a Structure from Motion (SfM) approach. The resulting 3D point cloud has supported as-built parametric modelling (Scan-to-BIM) with the consequent extraction of plans and sections. Finally, the Heritage/Historic Building Information Modelling (HBIM) model generated was rendered and tested for a VR-based immersive experience. Building Information Modelling (BIM) and virtual reality (VR) applications were tested as a support for the management of the building, the maintenance of the hydraulic system, and the training of qualiﬁed technicians. In addition, considering the historical value of the surveyed building, the methodology was also applied for dissemination purposes.


Introduction 1.Geomatics, HBIM and VR for Built Heritage Documentation
An accurate and georeferenced 3D survey of an architectural or engineering facility constitutes the source of metric information underlying the design of any technical intervention related to the management, maintenance and enjoyment of the facility itself [1,2].When dealing with large or complex constructions, geometric characterisation inevitably requires the integration of one or more geomatic surveying techniques: Terrestrial Laser Scanning (TLS) and digital terrestrial or aerial photogrammetry from an Unmanned Aircraft System (UAS) now constitute a production standard for the generation of three-dimensional point clouds [3][4][5].These techniques are often integrated by the use of Global Navigation Satellite System (GNSS) measurements, three-dimensional topographic surveying with total stations, and/or geometric or trigonometric levelling for inclusion in planimetric and altimetric absolute reference systems and for the integration of data derived from the various methodologies.From the point clouds obtained by surveying activities, it is possible to obtain metric information of different complexities: from simple measurements to the extraction of traditional two-dimensional representations (plans, elevations, sections) up to the construction, through a Heritage/Historic Building Information Modelling (HBIM) approach, of an as-built 3D model (Scan-to-BIM) [6,7].There are numerous examples in the literature of the HBIM of historic buildings, in which the challenges of the geometric restitution of unique and complex-shaped elements are addressed [8][9][10].The latter, enriched with information linked to the elements in a Building Information Modelling (BIM) context, can be additional support to meet both documentation and site management needs from a functional and/or conservative perspective [11,12].The same tools and processes are also widely used for the study and documentation of architectural and cultural heritage.In this field, the knowledge of objects becomes even more complex because it is enriched with the historical and artistic aspects of the objects.The possible purposes of surveying and modelling are also more varied, because the interest in dissemination is added to the purely technical aspects.In particular, the availability of digital models in the field of cultural heritage allows, for instance through virtual reality (VR), for their dissemination, and constitutes a tool that becomes irreplaceable in the case of no longer accessible or existing properties [13,14].In fact, VR technology can already be used in a workflow to generate realistic digital reproductions of historic buildings for immersive experiences [15,16].
The implementation of virtual environments for BIM and HBIM models has been increasingly explored in recent years.In general, a virtual environment can be seen as a potential container for different technologies and disciplines that contribute to the conservation, knowledge and dissemination of cultural heritage [17], objectives that are in line with those of BIM and HBIM.Thus, the combination of the two technologies, both of which aim at interoperability, interdisciplinarity and shareability, can be a great advantage in the world of built heritage.Even in the world of new constructions, the virtual navigation of a BIM model can generate certain advantages for various aspects and professional figures, as highlighted in [18], where a review of the scientific literature on the topic is carried out.Here, it is reported that the main fields of the application of VR for the BIM of new constructions are education, data exchange, and design/management.However, it is in the field of HBIM that virtual technologies find excellent use, becoming a valuable tool in the management of historic buildings.In [19], for example, an application of VR and HBIM is proposed for the risk awareness of an ancient building through the definition of metadata associated with the model for contextualised information retrieval in risk management.In [20,21], instead, HBIM and virtual technologies are used in combination for the purpose of the dissemination and communication of historical assets.Recently, in [22], an integrated approach of BIM, GIS (Geographic Information System) and VR/AR (Augmented Reality) is designed to propose a collaborative maintenance strategy for an ancient village.
In this paper, an example of combination of HBIM and VR technologies is offered, applying the designed methodology to a case of built industrial heritage and including all the topics mentioned so far.

Case Study
The case study refers to Battiferro lock (original name "Sostegno del Battiferro") in Bologna (Figure 1), a hydraulic work consisting of a building and a system of gates, built in 1439 on the Navile canal.The Battiferro lock is one of eight locks distributed throughout the city to facilitate navigation around the Navile canal [23], and its hydraulic system is still used to control the canal's waters at the entrance to the city.During the 1491 renovation of the Navile canal, Pietro Brambilla designed the wooden structure of the "Sostegno del Pero", which was later called "Sostegno del Battiferro" because of the water usage for iron and copper metallurgical work.Between the years 1547-1548, the structure was rebuilt by Jacopo Barozzi da Vignola (often simply called Vignola) in terracotta bricks produced in the nearby Galotti Furnace, with an octagonal navigation basin, lately modified several times.The manoeuvre building, located at the joint where the Navile branches off, used to be standing as a single building until it underwent a radical restructuring in 1914: another building was added, and the new spillway was built at the centre of the upper stream riverbed, to increase the mooring capacity and to serve the rice pile on the bank.The two buildings are functionally independent, the most recent having been used as the caretaker's residence.Both are built of brick masonry in Flemish bond, and the caretaker's house is coated with paint.On the main gate of the south façade of the manoeuvre building, a sandstone memorial crest is placed to commemorate the rebuilding works carried out by Vignola, which were commissioned by Pope Paul III Farnese.
Remote Sens. 2024, 16, x FOR PEER REVIEW 3 of 17 used to be standing as a single building until it underwent a radical restructuring in 1914: another building was added, and the new spillway was built at the centre of the upper stream riverbed, to increase the mooring capacity and to serve the rice pile on the bank.The two buildings are functionally independent, the most recent having been used as the caretaker s residence.Both are built of brick masonry in Flemish bond, and the caretaker s house is coated with paint.On the main gate of the south façade of the manoeuvre building, a sandstone memorial crest is placed to commemorate the rebuilding works carried out by Vignola, which were commissioned by Pope Paul III Farnese.Given the function of the facility and the strong industrial characterisation assumed by the surrounding area in the nineteenth and twentieth centuries, the Battiferro lock is an example of industrial archaeology, a particularly interesting topic for geomatics [24][25][26].The activities carried out by the DICAM geomatics group were realised in the framework of a collaboration with the UAS unit of the Italian Red Cross, Bologna Section, to meet the requests expressed by the Agency for the Territorial Safety and the Civil Protection of the Emilia-Romagna Region; the latter still employs the Battiferro hydraulic system to regulate the waters of the Navile at the entrance of the city and is in charge of the building management and conservation.

Objectives
The activities performed at the Battiferro lock were an application of modern geomatic techniques for updating the technical documentation of the hydraulic works under the responsibility of the regional service.The needs expressed were different: from framing into a geodetic reference system to metric documentation for the technical management of the buildings, from the possibility of supporting training activities for the technical personnel in charge of operating the sluice gate system to cultural dissemination related to the city s historical heritage.
In relation to the characteristics and function of the facility, the first objective was the inclusion of the work in a cartographic reference system, assuming as the altimetric datum the geoidal surface for the purposes of proper hydraulic modelling.Traditional graphic representations (plans, perspective drawings, sections) were produced at a scale of 1:200, which was considered appropriate for the extension and complexity of this site and the purpose of the work.In addition to the main building with the ancillary structures, upstream and downstream channels were also surveyed to obtain the general plan of the area and the contour lines map.To optimise the whole process of managing the works, it Given the function of the facility and the strong industrial characterisation assumed by the surrounding area in the nineteenth and twentieth centuries, the Battiferro lock is an example of industrial archaeology, a particularly interesting topic for geomatics [24][25][26].The activities carried out by the DICAM geomatics group were realised in the framework of a collaboration with the UAS unit of the Italian Red Cross, Bologna Section, to meet the requests expressed by the Agency for the Territorial Safety and the Civil Protection of the Emilia-Romagna Region; the latter still employs the Battiferro hydraulic system to regulate the waters of the Navile at the entrance of the city and is in charge of the building management and conservation.

Objectives
The activities performed at the Battiferro lock were an application of modern geomatic techniques for updating the technical documentation of the hydraulic works under the responsibility of the regional service.The needs expressed were different: from framing into a geodetic reference system to metric documentation for the technical management of the buildings, from the possibility of supporting training activities for the technical personnel in charge of operating the sluice gate system to cultural dissemination related to the city's historical heritage.
In relation to the characteristics and function of the facility, the first objective was the inclusion of the work in a cartographic reference system, assuming as the altimetric datum the geoidal surface for the purposes of proper hydraulic modelling.Traditional graphic representations (plans, perspective drawings, sections) were produced at a scale of 1:200, which was considered appropriate for the extension and complexity of this site and the purpose of the work.In addition to the main building with the ancillary structures, upstream and downstream channels were also surveyed to obtain the general plan of the area and the contour lines map.To optimise the whole process of managing the works, it was decided to proceed with a HBIM of the building, with the aim of enriching the 3D representation with attributes and information.To use the model for the training of the technicians and for the immersive exploration of the site for the purpose of cultural dissemination, experiments were conducted to explore the HBIM model with VR platforms, testing different systems that could provide distinct outcomes.

Methodology Overview
The overall workflow of the activities carried out, as shown in Figure 2, can be structured according to three main phases: the geomatic survey necessary for the construction of a georeferenced and accurate 3D model, the generation of a corresponding HBIM model, and finally the experimentation of an immersive exploration through the VR of the product obtained.The adopted methodologies will be described in detail in the following paragraphs in the same conceptual order.was decided to proceed with a HBIM of the building, with the aim of enriching the 3D representation with attributes and information.To use the model for the training of the technicians and for the immersive exploration of the site for the purpose of cultural dissemination, experiments were conducted to explore the HBIM model with VR platforms, testing different systems that could provide distinct outcomes.

Methodology Overview
The overall workflow of the activities carried out, as shown in Figure 2, can be structured according to three main phases: the geomatic survey necessary for the construction of a georeferenced and accurate 3D model, the generation of a corresponding HBIM model, and finally the experimentation of an immersive exploration through the VR of the product obtained.The adopted methodologies will be described in detail in the following paragraphs in the same conceptual order.

Survey Operations
The geometric survey was mainly conducted with a TLS system, aiming to obtain a cloud of real colour points of the entire area of interest, the building and its interior.But, given both the demands of completeness and precision required and the characteristics of the survey object itself, it has also been necessary to use several other geomatic techniques.The field operations were therefore preceded by a careful planning phase to achieve an optimal integration of the different methodologies.
For the georeferencing of the survey and the realisation of a reference system inserted in an official cartographic context, four three-dimensional points were materialised, chosen in such a way as to have a pair of inter-visible points on each side of the building (Ri points in Figure 3a).A GNSS Network-based Real Time Kinematic (NRTK) survey was first executed on two of these points to insert the area into the European Terrestrial Reference System (ETRS89), adopted by a Decree of the Italian Presidency of the Council by public administrations at the national level, using as a cartographic projection the Universal Transverse Mercator (UTM), zone 32N.A topographical network involving the four points was then measured by a high-precision total station (Leica TS30), to obtain cartographic reference coordinates for the subsequent processing of TLS data, with a relative accuracy of a few millimetres.Given the extreme importance of the hydraulic aspects for this type of infrastructure, the altimetric survey was carried out separately: two permanent altimetric references were materialised on the building, whose orthometric height

Survey Operations
The geometric survey was mainly conducted with a TLS system, aiming to obtain a cloud of real colour points of the entire area of interest, the building and its interior.But, given both the demands of completeness and precision required and the characteristics of the survey object itself, it has also been necessary to use several other geomatic techniques.The field operations were therefore preceded by a careful planning phase to achieve an optimal integration of the different methodologies.
For the georeferencing of the survey and the realisation of a reference system inserted in an official cartographic context, four three-dimensional points were materialised, chosen in such a way as to have a pair of inter-visible points on each side of the building (Ri points in Figure 3a).A GNSS Network-based Real Time Kinematic (NRTK) survey was first executed on two of these points to insert the area into the European Terrestrial Reference System (ETRS89), adopted by a Decree of the Italian Presidency of the Council by public administrations at the national level, using as a cartographic projection the Universal Transverse Mercator (UTM), zone 32N.A topographical network involving the four points was then measured by a high-precision total station (Leica TS30), to obtain cartographic reference coordinates for the subsequent processing of TLS data, with a relative accuracy of a few millimetres.Given the extreme importance of the hydraulic aspects for this type of infrastructure, the altimetric survey was carried out separately: two permanent altimetric references were materialised on the building, whose orthometric height was obtained by means of differential trigonometric precision levelling, starting from a benchmark of the Emilia Romagna geodetic network.The levelling sections totalling about 450 m long were measured forward and backward within the tolerance limits usually provided for high-precision geometric levelling (±2 √ L mm, with L in km units).
with algorithms based on Iterative Closest Point (ICP) methodology, thanks to the identification of common elements.
The activities concerning the outdoor areas were completed during maintenance work on the hydraulic system that required emptying the canals.In this way, it was possible to survey the part of the canals that is normally submerged.To supplement the data in the remaining submerged areas, several points were surveyed by total station from the points of the established reference network.Figure 3c shows the distribution of the elevation points obtained.Thanks to the high accuracy of the instrument used and the limited size of the survey area, it was possible to achieve standard deviations in the coordinates of these points of at most 1.5 mm.The TLS survey was carried out with a time-of-flight Riegl VZ400 laser scanner: it was necessary to carry out about thirty scans in the external area, and the same number was needed to complete the interior of the building.A total of about 300 million points were surveyed.Figure 3b shows the positions from which the scans were performed to complete the survey of the outdoor areas and the distribution of the retroreflective targets used for the alignment and georeferencing of the point clouds.For each pair of scans, the alignment was based on at least 4 common targets obtaining transformation root mean square errors (RMSE) between 2 and 7 mm.For the scans in the external area, the coordinates of the targets in the adopted reference system were obtained thanks to the topographical survey performed by total station from the points of the reference network.The 95% confidence error ellipses for the positions of the targets were calculated, and the values of the semi-major axes were less than or equal to 5 mm.On the contrary, for the retroreflective targets used inside the building, the total station survey was not realised.Therefore, for these scans, the alignment was first carried out in a local reference system.The co-registration between the overall external and internal clouds was then performed with algorithms based on Iterative Closest Point (ICP) methodology, thanks to the identification of common elements.
The activities concerning the outdoor areas were completed during maintenance work on the hydraulic system that required emptying the canals.In this way, it was possible to survey the part of the canals that is normally submerged.To supplement the data in the remaining submerged areas, several points were surveyed by total station from the points of the established reference network.Figure 3c shows the distribution of the elevation points obtained.Thanks to the high accuracy of the instrument used and the limited size of the survey area, it was possible to achieve standard deviations in the coordinates of these points of at most 1.5 mm.
To complete the geometric description of the building with the survey of the roofing and obtain a general plan of the area, a photogrammetric survey was finally performed by UAS, thanks to the collaboration with the UAS unit of the Italian Red Cross, Bologna Section.This was carried out in a manner consistent with current flight regulations, as the study area is located within an approaching area to the Bologna airport.The survey was conducted on a further working day before the filling of the canals.In the first phase, approximately 20 targets were distributed as Ground Control Points (GCPs) over the entire area and then surveyed in the adopted reference system using the GNSS-NRTK technique.Subsequently, the flights necessary to cover the entire area were realised according to aerial photogrammetry's traditional nadiral acquisition scheme.A DJI Mavic 2 Enterprise was used with a flight height of 20 m, obtaining a set of 450 images with a ground resolution of 6 mm.A second set of approximately 150 images was obtained from a further flight specifically dedicated to the building, and acquired according to a pattern of converging shots to render the model of the upper part of the building façades.The photogrammetric processing of the acquired images was carried out according to the Structure from Motion (SfM) algorithm, obtaining an average RMSE of 3.8 cm on the 20 GCPs.
Regarding the representation of the area, traditional CAD methods were used: the general planimetry was obtained by photogrammetric processing with the creation of an orthomosaic of the images, whilst the contour lines map and the longitudinal profiles of the canal bottom were extracted from the point cloud.For the building and the related hydraulic works, as already mentioned, it was decided to proceed with the generation of an HBIM model based on the union of the overall clouds of the interior and exterior, according to the methods that will be described in the corresponding section.
To complete the description of the surveys performed, it is also necessary to mention the detailed survey of the mechanical organs that govern the sluice gates and that are housed in the building's manoeuvring room.
The need for this survey emerged later during the implementation phase of the virtual reality exploration.Since the TLS survey was designed for a representation of the building on an architectural scale, the resulting point cloud did not allow the desired degree of detail to be achieved for the reconstruction of the objects in manoeuvring room.In fact, to be able to use virtual reality navigation not only for dissemination purposes but also for the remote training of personnel qualified to manoeuvre the gates in the event of an emergency, it was necessary to render all the mechanical components and their operation with a high degree of realism.All manoeuvring mechanisms were then scanned with a Structured Light Projection scanner (Artec EVA scanner) to obtain highly detailed meshes.
Figure 4 shows a summary of the equipment and operating methods used for the surveys described above.

HBIM Implementation
The 3D point cloud obtained was used as a starting point for HBIM to generate a coherent 3D model of the facility, accompanied by information content about the operation of the sluice gate system and the operating devices.This process allowed us to capture not only the geometric-dimensional aspects but also the historical and architectural features of the building.Indeed, the application of Scan-to-BIM approach is not only aimed at creating a 3D geometric as-built model, but should be understood as a process of data acquisition, analysis, and the development of knowledge about an asset [11,12].The topic of digitization of historic buildings using BIM methodology, in fact, takes on relevance when the use of the HBIM model allows the asset to be managed and maintained [27].

HBIM Implementation
The 3D point cloud obtained was used as a starting point for HBIM to generate a coherent 3D model of the facility, accompanied by information content about the operation of the sluice gate system and the operating devices.This process allowed us to capture not only the geometric-dimensional aspects but also the historical and architectural features of the building.Indeed, the application of Scan-to-BIM approach is not only aimed at creating a 3D geometric as-built model, but should be understood as a process of data acquisition, analysis, and the development of knowledge about an asset [11,12].The topic of digitization of historic buildings using BIM methodology, in fact, takes on relevance when the use of the HBIM model allows the asset to be managed and maintained [27].
The first phase of the workflow leading to the creation of the HBIM model was to evaluate the use of the considerable number of points acquired.The choice was made to subsample the point cloud by imposing an average interpoint spacing of 1 cm to work with lighter data, more suitable for the intended restitution purposes.In particular, the aim was to produce 2D graphic design drawings at a scale of 1:200, describing the state of the asset from an HBIM model that satisfied these final requirements.The resulting data, equipped with the RGB information, was imported within the BIM authoring software Autodesk Revit (2023.0.1 Hotfix version) used for modelling following its logic and procedures for importing point clouds.For this purpose, the ReCap (2023.0.1 Hotfix version) programme was used to obtain a compatible data format (.rcp) to be imported into Revit.
Modelling was initially focused on the two structurally independent buildings, including the architectural elements and mechanical equipment within the manoeuvring room.As anticipated, this is where the management operations of the sluice gate system responsible for controlling downstream water flows are concentrated.In view of the importance of the manoeuvring room and the mechanical equipment present, data sheets The first phase of the workflow leading to the creation of the HBIM model was to evaluate the use of the considerable number of points acquired.The choice was made to subsample the point cloud by imposing an average interpoint spacing of 1 cm to work with lighter data, more suitable for the intended restitution purposes.In particular, the aim was to produce 2D graphic design drawings at a scale of 1:200, describing the state of the asset from an HBIM model that satisfied these final requirements.The resulting data, equipped with the RGB information, was imported within the BIM authoring software Autodesk Revit (2023.0.1 Hotfix version) used for modelling following its logic and procedures for importing point clouds.For this purpose, the ReCap (2023.0.1 Hotfix version) programme was used to obtain a compatible data format (.rcp) to be imported into Revit.
Modelling was initially focused on the two structurally independent buildings, including the architectural elements and mechanical equipment within the manoeuvring room.As anticipated, this is where the management operations of the sluice gate system responsible for controlling downstream water flows are concentrated.In view of the importance of the manoeuvring room and the mechanical equipment present, data sheets and instructions on the management procedures of the gates control system were collected and implemented in the BIM model.To achieve this goal, information parameters and related data sheets were assigned to the mechanical BIM elements.The technical documentation of the electrical panels that govern the manoeuvring operations of the hydraulic organs has been associated with the relevant BIM element, through the compilation of a dedicated parameter, providing the link to the correspondent files.
In particular, this documentation concerns an exhaustive description of the overall functioning of the mechanical system, pdf files with the instructions for manoeuvring the gates, and detailed photos to better illustrate the buttons on the electrical panels.

Testing with VR Systems for HBIM Models
The use of BIM methodology, due the standardisation of data and processes, allows us to exploit the interoperability of data and models.Interoperability is defined as the ability of two or more systems or components to exchange information and to use the information that has been exchanged [27,28].
Through the use of BIM methodology, it was possible to obtain an IFC (Industry Foundation Classes) model containing the geometric and information assets, which allowed for implementation in platforms dedicated to exploration in VR.The IFC model from the BIM was explored in virtual reality using two different configurations (VR software + VR hardware).The two configurations were selected and developed to fulfil two different objectives: in the first case, the aim was to find a solution specifically designed for the exploration of BIM-constructed 3D models in VR, hence the more technical approach, while the second one was utilised for the purposes of visualisation and dissemination.
For the first configuration, the identified target was made up of technicians and experts in the AEC field (engineers, architects, etc.) who could find advantages in the exploration in VR of a building 3D model that retains some of the functionalities of BIM.The platform selected (SentioVR), developed ad hoc for navigation in the VR of IFC models, allowed us to take advantage of some BIM functionalities in a virtual environment: it is possible to take measurements of the building elements, to hide and reveal components, to take notes directly onto the objects, to acquire images and to host a virtual meeting with multiple users.Moreover, the transition from the BIM software is very smooth, because the application consists of a plug-in to be installed directly in Revit.After launching it, the IFC model is automatically optimised and transferred into a cloud space to be accessed directly from the VR headset.The users receive a code to enter their personal space, from which the BIM models are accessible.Once in, it is possible to navigate the virtual environment of the BIM model and to easily use the integrated functionalities of the platform.The navigation modes are multiple: fly, walk, and teleport, allowing for a user-friendly exploration of the virtual scene.From the hardware side, the application is developed to be used in combination with the consumer-grade all-in-one Oculus MetaQuest headset (screen resolution 1832 × 1920 pixels, refresh rate up to 90 Hz).Hence, this device was used to explore the model in VR.
The procedure for the second aim, more focused on rendering aspects, has been envisaged with a view to the potential use of the products for the dissemination of the cultural aspects of the site.The platform selected, Twinmotion (2022.2.3 version), is a rendering software that allows us to apply materials properties to the elements of a BIM model, and to add animations, annotations, and additional elements in 2D and 3D.First, the IFC model of the Battiferro lock was converted into the Datasmith format that allows for a direct import from Revit to Twinmotion; then, the geometric model was textured with several materials associated with each element by carefully inspecting images of the building, visually recreating the materials of its real-word counterpart.Animations and textual elements were also added to increase the immersivity and interactivity of the virtual environment.For instance, the manoeuvring organs and the gates were associated with a rotation and translation animation, respectively, to simulate the functioning operations of the hydraulic system.The platform used allowed us to easily add an animation component to the individual elements of the model, and to activate them by entering a defined trigger area once in the virtual environment.Some textual information was added to indicate and shortly describe the main elements in the site (building one, building two, canal basin, manoeuvring room, etc.).Finally, the output was visualised using a professional-level VR headset (HTC Vive Pro 2), with a screen resolution of 4896 × 2448 pixels and a refresh rate of up to 120 Hz.This type of headset is not all-in-one but requires a cabled connection with a computer presenting high-level specifications, especially in terms of Graphics Processing Unit.

Survey Products
The integration of different geomatic techniques made it possible to obtain a 3D global point cloud of the building interiors and exteriors, and of the surrounding area, with a high precision and point density.The geodetic-topographical surveys allowed us to accurately orient the 3D products in a global reference system, as required.The survey project was successful, providing final graphic and 3D products that met the required levels of accuracy and detail.The photogrammetric processing made it possible to complete the final cloud by integrating the TLS survey and to obtain a complete orthomosaic of the general plan of the area with a ground sample distance of 7 mm (Figure 5).These products formed the basis for producing the final graphic drawings, HBIM model, and VR application.The accuracies obtained are widely compatible with the 1:200 representation scale defined in the design phase.
dicate and shortly describe the main elements in the site (building one, building two, canal basin, manoeuvring room, etc.).Finally, the output was visualised using a professionallevel VR headset (HTC Vive Pro 2), with a screen resolution of 4896 × 2448 pixels and a refresh rate of up to 120 Hz.This type of headset is not all-in-one but requires a cabled connection with a computer presenting high-level specifications, especially in terms of Graphics Processing Unit.

Survey Products
The integration of different geomatic techniques made it possible to obtain a 3D global point cloud of the building interiors and exteriors, and of the surrounding area, with a high precision and point density.The geodetic-topographical surveys allowed us to accurately orient the 3D products in a global reference system, as required.The survey project was successful, providing final graphic and 3D products that met the required levels of accuracy and detail.The photogrammetric processing made it possible to complete the final cloud by integrating the TLS survey and to obtain a complete orthomosaic of the general plan of the area with a ground sample distance of 7 mm (Figure 5).These products formed the basis for producing the final graphic drawings, HBIM model, and VR application.The accuracies obtained are widely compatible with the 1:200 representation scale defined in the design phase.Thanks to Structured Light Projection scanning, a high-detailed 3D mesh (0.5 mm 3D resolution) was obtained for the manoeuvring organs, accurately representing all their mechanical components.Figure 6 shows the comparison between the detail of a control wheel from the TLS-derived point cloud and the mesh obtained with the Structured Light Projection scanner.
of the building obtained from the photogrammetric processing.
Thanks to Structured Light Projection scanning, a high-detailed 3D mesh (0.5 mm 3D resolution) was obtained for the manoeuvring organs, accurately representing all their mechanical components.Figure 6 shows the comparison between the detail of a control wheel from the TLS-derived point cloud and the mesh obtained with the Structured Light Projection scanner.

HBIM Model
As discussed in Section 2.2, the point cloud model optimised for the Scan-to-BIM process resulted in a HBIM model consistent with the aims of the project.
The elements that are represented in the point cloud by discretizing them into points are returned geometrically in the BIM environment with parametric BIM objects.For the generation of the HBIM model, the challenge was to obtain a 3D digital representation that fulfils the intended purpose and has adequate geometric accuracy.For the proposed case, Revit standard elements were used for the building components, while the use of

HBIM Model
As discussed in Section 2.2, the point cloud model optimised for the Scan-to-BIM process resulted in a HBIM model consistent with the aims of the project.
The elements that are represented in the point cloud by discretizing them into points are returned geometrically in the BIM environment with parametric BIM objects.For the generation of the HBIM model, the challenge was to obtain a 3D digital representation that fulfils the intended purpose and has adequate geometric accuracy.For the proposed case, Revit standard elements were used for the building components, while the use of model in-place was employed for the irregularly shaped and unique elements, such as the external concrete hydraulic artefacts.As shown in Figure 7, the final result is derived from a close overlap between the point cloud model and the BIM model.Considering that the Level of Development (LOD) is difficult to define in heterogeneous cases, such as the one proposed, according to the ISO 19650-1 standard (https://www.iso.org/standard/68078.html consulted on 23 July 2024), the use of the concept of LOIN (Level of Information Need) would be more useful to define the HBIM model.In particular, both the input information parameters and the geometric accuracy of the constituent elements were defined a priori, in relation to the intended purposes that depend on its subsequent use, such as documentation and future maintenance and management.The manual process of modelling the architectural, structural and mechanical elements involved the use of considerable resources by modellers in terms of man-hours.It is important to emphasise, however, the benefit that comes from applying the BIM methodology, which certainly requires a large initial investment against a significantly more cost-effective use in the final stages of design; in this case, the operation and maintenance phases [27].
a close overlap between the point cloud model and the BIM model.Considering that the Level of Development (LOD) is difficult to define in heterogeneous cases, such as the one proposed, according to the ISO 19650-1 standard (https://www.iso.org/standard/68078.html consulted on 23 July 2024), the use of the concept of LOIN (Level of Information Need) would be more useful to define the HBIM model.In particular, both the input information parameters and the geometric accuracy of the constituent elements were defined a priori, in relation to the intended purposes that depend on its subsequent use, such as documentation and future maintenance and management.The manual process of modelling the architectural, structural and mechanical elements involved the use of considerable resources by modellers in terms of man-hours.It is important to emphasise, however, the benefit that comes from applying the BIM methodology, which certainly requires a large initial investment against a significantly more cost-effective use in the final stages of design; in this case, the operation and maintenance phases [27].Regarding the mechanical equipment, the highly detailed 3D meshes obtained with Structured Light Projection scanning were optimised to facilitate their import into the BIM software, ensuring that all the elements remained visible and easily distinguishable.The optimised meshes were converted from .obj to .dxfformat to be imported within the Revit work environment and later used to create a more immersive VR experience.An interesting aspect was found in diversifying the choice of the geometric restitution of these elements according to the intended purpose of the BIM model and element use.
The external area belonging to the Battiferro lock complex was modelled in a BIM environment using point cloud data to generate a topographic surface, as shown in Figure 8a.Since all the survey products are georeferenced, it is possible to integrate the HBIM model in a GIS environment (Figure 8b).Regarding the mechanical equipment, the highly detailed 3D meshes obtained with Structured Light Projection scanning were optimised to facilitate their import into the BIM software, ensuring that all the elements remained visible and easily distinguishable.The optimised meshes were converted from .obj to .dxfformat to be imported within the Revit work environment and later used to create a more immersive VR experience.An interesting aspect was found in diversifying the choice of the geometric restitution of these elements according to the intended purpose of the BIM model and element use.
The external area belonging to the Battiferro lock complex was modelled in a BIM environment using point cloud data to generate a topographic surface, as shown in Figure 8a.Since all the survey products are georeferenced, it is possible to integrate the HBIM model in a GIS environment (Figure 8b).
The integration of BIM models in a GIS environment brings significant benefits when the spatial component is an objective advantage for its life-cycle management [29,30].In the specific case of the Battiferro lock, given the important role of the system in managing water streams in the canals, having extensive spatial information allows for several factors useful for its operation to be considered.In addition, this hydraulic work is managed, as mentioned, by the Agency for the Territorial Safety and the Civil Protection of the Emilia-Romagna Region, which very regularly uses GIS platforms for spatial data analysis and management and, therefore, are relevant operational tools for their activities.The goal of the proposed workflow is to provide local governments with tools that can optimise their operations by taking advantage of modern technologies and data interoperability [30].
For the maintenance of the two buildings and the assessment of structural behaviour, a future development could be the application of the Cloud2FEM procedure [31,32], which would allow for the implementation of a FEM model and the analysis of the structural behaviour of the asset [33].The integration of BIM models in a GIS environment brings significant benefits when the spatial component is an objective advantage for its life-cycle management [29,30].In the specific case of the Battiferro lock, given the important role of the system in managing water streams in the canals, having extensive spatial information allows for several factors useful for its operation to be considered.In addition, this hydraulic work is managed, as mentioned, by the Agency for the Territorial Safety and the Civil Protection of the Emilia-Romagna Region, which very regularly uses GIS platforms for spatial data analysis and management and, therefore, are relevant operational tools for their activities.The goal of the proposed workflow is to provide local governments with tools that can optimise their operations by taking advantage of modern technologies and data interoperability [30].
For the maintenance of the two buildings and the assessment of structural behaviour, a future development could be the application of the Cloud2FEM procedure [31,32], which would allow for the implementation of a FEM model and the analysis of the structural behaviour of the asset [33].

HBIM to VR Implementation
The results of the HBIM-VR combination made it possible to enhance the products of geomatics and their direct use both for technical and functional purposes, and for the enhancement of an important example of the area s industrial heritage.The BIM-oriented platform was particularly effective for the technical audience, since it allowed us to inspect

HBIM to VR Implementation
The results of the HBIM-VR combination made it possible to enhance the products of geomatics and their direct use both for technical and functional purposes, and for the enhancement of an important example of the area's industrial heritage.The BIM-oriented platform was particularly effective for the technical audience, since it allowed us to inspect the elements in the model and visualise some information related to them as BIM categories, and family, object name, materials, etc. (Figure 9a).Moreover, it facilitated the possibility of adding annotations and images, hosting virtual meetings and taking measurements; functionalities that can have several advantages in the context of collaborative management and maintenance.Nevertheless, the graphic rendering of the model is simplified and optimised for VR by the platform, which employs non-controllable strategies during the model upload to the cloud space for visualisation.In addition, the use of a consumer-grade VR headset, which does not present a very high resolution (Figure 9a), did not allow for a high-quality graphical rendering of the virtual environment.
The other VR platform tested, instead, permitted us to obtain a high-quality virtual experience, thanks to the addition of realistic textures to the objects' materials, the presence of animations, and shading/lighting and sound effects, enhancing the level of immersivity in the virtual environment (Figure 9b).Nevertheless, the technical content was limited to text annotations associated with some areas of the model.Moreover, the use of the high-end VR headset, albeit permitting a high-resolution graphical rendering, requires a cabled connection with a computer, making this kind of set up not very portable nor user-friendly.This second option, then, can be considered as an effective tool to share the historical significance of the Battiferro lock, for instance in museum applications, while the first platform can be orientated to the technical audience involved in the site management.
Overall, both the platforms/headsets tested allowed us to obtain the desired result of creating a virtual experience out of the HBIM model of the surveyed building with a user-friendly approach, since none of them require coding skills to be implemented.
plified and optimised for VR by the platform, which employs non-controllable strategies during the model upload to the cloud space for visualisation.In addition, the use of a consumer-grade VR headset, which does not present a very high resolution (Figure 9a), did not allow for a high-quality graphical rendering of the virtual environment.
The other VR platform tested, instead, permitted us to obtain a high-quality virtual experience, thanks to the addition of realistic textures to the objects materials, the presence of animations, and shading/lighting and sound effects, enhancing the level of immersivity in the virtual environment (Figure 9b).Nevertheless, the technical content was limited to text annotations associated with some areas of the model.Moreover, the use of the high-end VR headset, albeit permitting a high-resolution graphical rendering, requires a cabled connection with a computer, making this kind of set up not very portable nor userfriendly.This second option, then, can be considered as an effective tool to share the historical significance of the Battiferro lock, for instance in museum applications, while the first platform can be orientated to the technical audience involved in the site management.Overall, both the platforms/headsets tested allowed us to obtain the desired result of creating a virtual experience out of the HBIM model of the surveyed building with a userfriendly approach, since none of them require coding skills to be implemented.

Conclusions
The paper deals with the topographic survey, 3D modelling, representation and use through HBIM and VR techniques of the hydraulic system of the Battiferro lock in Bologna, Italy.The described work is based on a robust connection to the geodetic reference systems recognised internationally and at the national level.Thanks to the use of GNSS techniques, it was possible to refer the entire project to the European Terrestrial Reference System ETRS89.Since this is a hydraulic contest, particular attention was paid to the definition of the altimetric datum, and the altimetric connection of the entire project to a system of elevations referred to the geoid.
Furthermore, considering the achieved accuracies, this is evidently an example of a rigorous work of integration between all the main techniques offered nowadays by geomatics, applied to a case of industrial archaeology, in a technical context governed by engineering, management and dissemination requirements, and linked to hydraulic works whose origins date back to 1439.
On the other hand, some considerations are necessary as a conclusion to this work.First of all, the integrated methodology presented required considerable effort in terms of

Conclusions
The paper deals with the topographic survey, 3D modelling, representation and use through HBIM and VR techniques of the hydraulic system of the Battiferro lock in Bologna, Italy.The described work is based on a robust connection to the geodetic reference systems recognised internationally and at the national level.Thanks to the use of GNSS techniques, it was possible to refer the entire project to the European Terrestrial Reference System ETRS89.Since this is a hydraulic contest, particular attention was paid to the definition of the altimetric datum, and the altimetric connection of the entire project to a system of elevations referred to the geoid.
Furthermore, considering the achieved accuracies, this is evidently an example of a rigorous work of integration between all the main techniques offered nowadays by geomatics, applied to a case of industrial archaeology, in a technical context governed by engineering, management and dissemination requirements, and linked to hydraulic works whose origins date back to 1439.
On the other hand, some considerations are necessary as a conclusion to this work.First of all, the integrated methodology presented required considerable effort in terms of resources, time and expertise involved.This type of application, ranging from the topographical survey to the creation of a virtual environment, is not a trivial process and requires multidisciplinary collaboration and teamwork.This latter aspect, which at first glance may appear to be critical due to the heterogeneity in the requirements of the different detection techniques, was on the contrary one of the main strong points of this experiment.
Moreover, from a technical point of view, the virtual reality experiments carried out were beneficial for the visualisation of the BIM model and the exploration of the site, but presented some limitations in terms of immersivity and interactivity.A higher level of technological implementation in virtual environments can only be achieved through the use of scripting within game development engines.For the purposes of this work, the proposed applications were deemed sufficient, but could be improved in the future by implementing interactive components in the virtual scenario (animations, additional multimedia elements, user-object interactions) that would increase the impact of the virtual model on the users involved.
Another aspect that needs to be further developed to enrich the site's knowledge concerns the building's constituent materials and their state of preservation.The data collected during the survey campaign and digital modelling can already be used as a basis for visualising various types of information associated with the Battiferro Lock, which in the future can be integrated with other data about materials, diagnostic analyses performed, restoration operations, and maintenance strategies.Through interdisciplinary collaboration, the knowledge of the building can be deepened at various levels, and this would bring additional benefit to the maintenance and preservation of the site.

Figure 1 .
Figure 1.The Battiferro lock: view of the main building and upstream canals.

Figure 1 .
Figure 1.The Battiferro lock: view of the main building and upstream canals.

Figure 2 .
Figure 2. Workflow of activities for the survey, HBIM and VR implementation for the Battiferro lock.

Figure 2 .
Figure 2. Workflow of activities for the survey, HBIM and VR implementation for the Battiferro lock.

Figure 3 .Figure 3 .
Figure 3. Geomatics survey activities: (a) survey area and reference points: the yellow triangles represent the 3D points measured with GNSS-NRTK and total station, the blue circles indicate the elevation landmarks measured with trigonometric levelling; (b) the scan positions of the laser scannerFigure 3. Geomatics survey activities: (a) survey area and reference points: the yellow triangles represent the 3D points measured with GNSS-NRTK and total station, the blue circles indicate the elevation landmarks measured with trigonometric levelling; (b) the scan positions of the laser scanner system and distribution of the retro-reflective targets: the white squares indicate the position of the targets, the scan positions are the red triangles with the black border when they were taken below ground level (under the building or in the canals); (c) additional detailed survey of the channel bottom: the circles represent the elevation points measured with total station from the reference points.

Figure 4 .
Figure 4. Summary of geomatic tools and techniques used for the survey of the Battiferro Lock.

Figure 4 .
Figure 4. Summary of geomatic tools and techniques used for the survey of the Battiferro Lock.

Figure 5 .
Figure 5. Products of the UAS photogrammetric survey: (a) orthomosaic of the surveying area: yellow circles indicate the position of the GCPs; (b) detail of the point cloud of the exterior of the building obtained from the TLS survey coloured in greyscale; (c) detail of the point cloud in real colours of the building obtained from the photogrammetric processing.

Figure 6 .
Figure 6.Three-dimensional models of a control wheel: (a) portion of the point cloud derived from TLS, (b) mesh obtained with the Structured Light Projection scanner; (c) BIM object; (d) mesh used in VR.

Figure 6 .
Figure 6.Three-dimensional models of a control wheel: (a) portion of the point cloud derived from TLS, (b) mesh obtained with the Structured Light Projection scanner; (c) BIM object; (d) mesh used in VR.

Figure 7 .
Figure 7. Three-dimensional view of the BIM model superimposed to the point cloud model.

Figure 7 .
Figure 7. Three-dimensional view of the BIM model superimposed to the point cloud model.

Figure 8 .
Figure 8. BIM models: (a) 3D view in BIM platform; (b) 3D view of the BIM model imported in a GIS platform.

Figure 8 .
Figure 8. BIM models: (a) 3D view in BIM platform; (b) 3D view of the BIM model imported in a GIS platform.

Figure 9 .
Figure 9.Comparison between the tested VR navigation platforms: (a) the technical platform, allowing the user to select elements and visualise the BIM data associated with them; (b) the rendering platform, offering a realistic and impacting virtual representation of the HBIM model.