An HBIM Methodology for the Accurate and Georeferenced Reconstruction of Urban Contexts Surveyed by UAV: The Case of the Castle of Charles V

Round 1

Reviewer 1 Report

This paper describe the procedures of digitization of the built heritage by using Scan-to-BIM approach. The paper is well written and organized. 

The subject of the paper is very modern. Development of realistic 3D models of the cultural heritage is beneficial in many ways, from monitoring the condition of the building through the time to detecting damage and making decisions on conservation. The paper shows good results and indicates directions for future improvement of the procedures. 

I have few remarks. It would be good to define abbreviation HBIM somewhere in the introduction and to check for other abbreviations too.

line 49  - cloud cloud

It would be interesting to the readers if the authors mention the equipment and software they used, whether they may have made some software themselves.

Also, a remark on the methods how this model can expanded with the indoor data can be added.

Author Response

We wish to thank the reviewer for their suggestions and their meticulous review of our manuscript.

We tried our best to address all their comments.

This paper describes the procedures of digitization of the built heritage by using Scan-to-BIM approach. The paper is well written and organized. 

The subject of the paper is very modern. Development of realistic 3D models of the cultural heritage is beneficial in many ways, from monitoring the condition of the building through the time to detecting damage and making decisions on conservation. The paper shows good results and indicates directions for future improvement of the procedures. 

I have few remarks. It would be good to define abbreviation HBIM somewhere in the introduction and to check for other abbreviations too.

Reply: According to the reviewer's suggestion, a brief explanation of the meaning of HBIM (Historic Building Information Modelling) has been added in paragraph 1.4 at the lines [116-128].

Here follows the added text at lines [116-128]: “Indeed, even though the modelling/conversion effort required for creating semantic BIMs from unstructured survey data is high and notable are the difficulties connected to accurately representing the variety of complex and irregular objects occurring in existing buildings and the lack of standards for their representation, the manual modelling and parametrising of existing architectural elements is still the most accurate way to interpret them. This is a common practice that aims to develop a library of reusable parametric objects for an efficient implementation of the Historic Building Information Modelling (HBIM) methodology [32]. HBIM is a renowned solution whereby interactive parametric objects representing architectural elements are constructed from historic data, these elements (including detail behind the scan surface) are usually accurately mapped onto integrated survey data; point cloud segmentation and orthoimages integration are two of the most suitable approaches for the purpose [33], going in the direction of artificial intelligence algorithms implementation.”

line 49  - cloud cloud

The reported mistake is not actually a repetition, but since the "cloud could" alliteration may sound not that clear, we opted for relacing it with “cloud makes it possible to” at lines [49-50].

It would be interesting to the readers if the authors mention the equipment and software they used, whether they may have made some software themselves.

Reply: According to the reviewer's suggestion, the equipment and software used were generically mentioned in paragraphs 2.2 and 2.3 (and the corresponding sub-paragraphs) and graphically resumed in Figure 1, Figure 2, and Figure 3. They are then better clarified in paragraphs 3.2 (and its sub-paragraphs) and 3.3, by adding the photogrammetric software employed at lines [484-485], and reformulating paragraph 3.3 at lines [507-512], also clarifying the originality of the VPL scripts all of which were designed by the authors.

Here follows the added text al lines [484-485]: “elaborated within the Agisoft Metashape environment”.

Here follows the modified text al lines [507-512]: “To achieve a metrically reliable HBIM model, a manual Scan-to-BIM approach - within the Autodesk Revit environment - was applied, for the modelling of the architectural BIM objects aiming at keeping them updatable at any time. On the other hand, a Mesh-to-BIM implementation - via ad-hoc, albeit repeatable, VPL scripts all of which were designed by the authors employing the Dynamo tool for Revit - was proposed for those unique elements of the built environment, i.e.”

Also, a remark on the methods how this model can expanded with the indoor data can be added.

Reply: According to the reviewer's suggestion, the conclusions were enriched with possible future developments related to the integrated use of TLS and close-range photogrammetry for indoor applications at lines [666-670].

Here follows the added text al lines [666-670]: “Future developments will certainly try to combine TLS and close-range photogrammetry data for indoor applications. This type of integrated data will initially be used for the manual BIM model of the main structure but also represents an interesting challenge if used as the source for the proposed procedural workflows, implementing triangulated mesh models derived from both the laser and the entire integrated dataset.”

Author Response File: Author Response.docx

Reviewer 2 Report

It is an actual and interesting investigation. Application of UAV (or Remote Operative Vehicles - ROV) allows effectively and promptly to construct digitize models of studied urban objects. First of all, these are archaeological and historical objects. The authors' description is comprehensive, but has some similarity with a technical report.

I suggest

1. It is necessary to add in the Introduction at least one paragraph describing the role of the UAV (ROV) in modern scientific, engineering, and archaeological investigations. A several references for this addition:

Eppelbaum, L.V. and Mishne, A.R., 2011. Unmanned Airborne Magnetic and VLF investigations: Effective Geophysical Methodology of the Near Future. Positioning, 2, No. 3, 112-133. 

Hadjimitsis, D.G., Agapiou, A., Themistocleous, K., Alexakis, D.D. and Sarris, A., 2013. Remote Sensing for Archaeological Applications: Management, Documentation and Monitoring. In: (Hadjimitsis, D. et al., Eds.), Remote Sensing of Environment: Integrated Approaches, InTech, 57-95.

Silverberg, L.M. and Bieber, C., 2014. Central Command Architecture for High-Order Autonomous Unmanned Aerial Systems. Intelligent Information Management, 6, 183-195.  

2. Conclusions should contain some concrete suggestions for the further improvement of the available methodology.   

Author Response

We wish to thank the reviewer for their suggestions and their meticulous review of our manuscript. We tried our best to address all their comments.

It is an actual and interesting investigation. Application of UAV (or Remote Operative Vehicles - ROV) allows effectively and promptly to construct digitize models of studied urban objects. First of all, these are archaeological and historical objects. The authors' description is comprehensive, but has some similarity with a technical report. 

I suggest

1. It is necessary to add in the Introduction at least one paragraph describing the role of the UAV (ROV) in modern scientific, engineering, and archaeological investigations. A several references for this addition:

Eppelbaum, L.V. and Mishne, A.R., 2011. Unmanned Airborne Magnetic and VLF investigations: Effective Geophysical Methodology of the Near Future. Positioning, 2, No. 3, 112-133. 

Hadjimitsis, D.G., Agapiou, A., Themistocleous, K., Alexakis, D.D. and Sarris, A., 2013. Remote Sensing for Archaeological Applications: Management, Documentation and Monitoring. In: (Hadjimitsis, D. et al., Eds.), Remote Sensing of Environment: Integrated Approaches, InTech, 57-95.

Silverberg, L.M. and Bieber, C., 2014. Central Command Architecture for High-Order Autonomous Unmanned Aerial Systems. Intelligent Information Management, 6, 183-195.  

Reply: According to the reviewer’s suggestion, we have included a new paragraph 1.2 regarding “UAS Photogrammetric Survey” at lines [59-76] to describe the evolution of UAS, emphasizing the difference between the acronyms UAV, UAS and ROV (Remote Operative Vehicles), and clarify the terminology chosen for the text.

Here follows the added text at lines [59-76]: “Unmanned Aerial Systems (UASs), known under various names and acronyms, such as Unmanned Aerial Vehicles (UAVs) – although the latter technically correspond to the sole drone supporting the system constituted of both the aerial vehicle and the sensor mounted on it –, Remotely Piloted Aerial Systems or simply drones [8], are aircraft without a pilot on board, that are being continuously miniaturized and have become widely accessible for commercial use [9–11]. In the last years, thanks to recent technological developments, remotely controlled aerial vehicles are increasingly used in support of geophysical surveys, enabling reliable 3D models [12–14]. UAS-based data collection is becoming increasingly cost-effective due to increased precision and accuracy and the ability to cover large areas inaccessible by land, with shorter flights and faster acquisition planning [15]. In particular, aerial photogrammetry from UAS has been used extensively in archaeology and cultural heritage for the documentation and 3D mapping of sites, thanks to innovative low-cost systems and high-resolution digital cameras [16,17], enabling the construction of 3D models with photorealistic textures [18].

For the purposes of the present discussion, the acronym UAV was chosen when referring to aerophotogrammetric surveying, as it is the most common terminology found in the literature.”

2. Conclusions should contain some concrete suggestions for the further improvement of the available methodology.   

Reply: According to the reviewer's suggestion, the conclusions were enriched with possible future developments related to the integrated use of TLS and close-range photogrammetry for indoor applications at lines [666-670].

Here follows the added text al lines [666-670]: “Future developments will certainly try to combine TLS and close-range photogrammetry data for indoor applications. This type of integrated data will initially be used for the manual BIM model of the main structure but also represents an interesting challenge if used as the source for the proposed procedural workflows, implementing triangulated mesh models derived from both the laser and the entire integrated dataset.”

Author Response File: Author Response.docx

Reviewer 3 Report

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 4 Report

Definitely, it is a nice piece of paper.

I have only minor issues related with the presentation. The first of all is the use of the term UAV. With all due respect, I find more accurate to talk about UAS (Unmanned Aerial System) unless you are only referring to the drone.

Secondly, I would like to suggest using a URL shortener, like bitly, to name a URL address.

Thirdly a table summarizing the data would be very useful in paragraph 3.2.1.

Finally,  I find Figure 8 very small.

Author Response

We wish to thank the reviewer for their suggestions and their meticulous review of our manuscript.

We tried our best to address all their comments.

Definitely, it is a nice piece of paper.

I have only minor issues related with the presentation. The first of all is the use of the term UAV. With all due respect, I find more accurate to talk about UAS (Unmanned Aerial System) unless you are only referring to the drone.

Reply: According to the reviewer’s suggestion, we have included a new paragraph 1.2 regarding “UAS Photogrammetric Survey” at lines [59-76] to describe the evolution of UAS, emphasizing the difference between the acronyms UAV, UAS and ROV (Remote Operative Vehicles), and clarify the terminology chosen for the text.

Here follows the added text at lines [59-76]: “Unmanned Aerial Systems (UASs), known under various names and acronyms, such as Unmanned Aerial Vehicles (UAVs) – although the latter technically correspond to the sole drone supporting the system constituted of both the aerial vehicle and the sensor mounted on it –, Remotely Piloted Aerial Systems or simply drones [8], are aircraft without a pilot on board, that are being continuously miniaturized and have become widely accessible for commercial use [9–11]. In the last years, thanks to recent technological developments, remotely controlled aerial vehicles are increasingly used in support of geophysical surveys, enabling reliable 3D models [12–14]. UAS-based data collection is becoming increasingly cost-effective due to increased precision and accuracy and the ability to cover large areas inaccessible by land, with shorter flights and faster acquisition planning [15]. In particular, aerial photogrammetry from UAS has been used extensively in archaeology and cultural heritage for the documentation and 3D mapping of sites, thanks to innovative low-cost systems and high-resolution digital cameras [16,17], enabling the construction of 3D models with photorealistic textures [18].

For the purposes of the present discussion, the acronym UAV was chosen when referring to aerophotogrammetric surveying, as it is the most common terminology found in the literature.”

Secondly, I would like to suggest using a URL shortener, like bitly, to name a URL address.

Reply: According to the reviewer’s suggestion, we used bitly to shorten URLs in the footnotes.

Thirdly a table summarizing the data would be very useful in paragraph 3.2.1.

Reply: According to the reviewer’s suggestion, a table summarizing the UAV survey data has been added in paragraph 3.2.1. at lines [491-492].

Finally, I find Figure 8 very small.

Reply: According to the reviewer’s suggestion, Figure 8 at line [553] has been slightly modified and enlarged to make it more understandable.

Author Response File: Author Response.docx

Reviewer 5 Report

The article is well written and original. Well-written introduction and research description.

The article has some minor errors and inaccuracies that require clarification:

Authors should answer the question what is the purpose of the scan? Is the general shape of the building suitable for e.g. early appraisal of renovation works, or is it an assessment of the technical condition of the building or, for example, the reconstruction of ornaments, bas-reliefs, etc.?

Each such goal requires a different accuracy of measurement - is it, then, sufficient? And what is the difference between ground-based scanning and UAV scanning?

For minor remarks, e.g. when observing the procedural workflow in Fig. 1 or subsequent, the recording formats were specified, e.g. in Fig. 1 ortho image in PNG. Is it not possible to use other formats, e.g. for ortho photos?

Author Response

We wish to thank the reviewer for their suggestions and their meticulous review of our manuscript.

We tried our best to address all their comments.

The article is well written and original. Well-written introduction and research description.

The article has some minor errors and inaccuracies that require clarification:

Authors should answer the question what is the purpose of the scan? Is the general shape of the building suitable for e.g. early appraisal of renovation works, or is it an assessment of the technical condition of the building or, for example, the reconstruction of ornaments, bas-reliefs, etc.? Each such goal requires a different accuracy of measurement - is it, then, sufficient? And what is the difference between ground-based scanning and UAV scanning?

Reply: According to the reviewer's suggestion, at lines [442-459] the initial purpose of the survey campaign was specified, namely to have reality-based model of the fortress's exterior as a basis for activities aimed at promoting and valorising the Italian cultural heritage. The integrated survey, obtained by combining UAV and TLS data, was carried out with the purpose of filling the gaps in both clouds, consisting of large portions of the castle that were not surveyed due to dense vegetation, resulting in a multiscale base model suitable for an initial evaluation of potential maintenance and restoration interventions.

Here follows the added text at lines [442-459]: “TLS and photogrammetric techniques have advantages and disadvantages; discriminating becomes the project budget rather than the required objectives or level of detail. Photogrammetric techniques require experience, above all in the acquisition phase, in order to obtain an accurate final result; TLS, on the other hand, while easy to use, requires experience in setting up the parameters and is a highly time-consuming and costly activity. The choice of which method to use depends mainly on the complexity of the site to be investigated, the accuracy requirements, and the budget and time available. For this reason, the integration of multiple techniques is often the most suitable solution.

The initial purpose of the survey campaign was the documentation for its posterior valorisation of the Crotone Fortress’ exteriors; a reality-based model of the Castel and its surroundings was then acquired employing integrated survey techniques to serve as a basis for those dissemination activities aimed at promoting the Italian cultural heritage. The integrated survey, obtained by combining UAV and TLS data, was carried out with the purpose of filling the gaps in both clouds, consisting of large portions of the castle that were not surveyed due to dense vegetation. The resulting three-dimensional multiscale model was, therefore, suitable for the development of sufficiently detailed HBIM models and for an initial assessment of possible maintenance and restoration work.”

For minor remarks, e.g. when observing the procedural workflow in Fig. 1 or subsequent, the recording formats were specified, e.g. in Fig. 1 ortho image in PNG. Is it not possible to use other formats, e.g. for ortho photos?

Reply: According to the reviewer's suggestion, we have added a clarification at lines [314-318] that clarifies the choice of proposed formats. Indeed, from the analysis we conducted, comparing the results obtained, the PNG format is the one that leads to the best rendering results, within the Revit environment, when compared to other formats, such as TIFF and JPG.

Here follows the added text at lines [314-318]: “It is worth clarifying that, although the most common formats for orthoimages, such as TIFF and JPG, are equally adequate to be imported as textures into Revit's material browser, PNG is the one that leads to the best rendering results, due to the possibility of maintaining a transparent background and at the same time an optimal resolution/compression ratio.”

Author Response File: Author Response.docx