Digital Data and Semantic Simulation—The Survey of the Ruins of the Convent of the Paolotti (12th Century A.D.)
Round 1
Reviewer 1 Report
The topic is interesting, but several issues have to be improved or clarified for the article to be published.
The authors must indicate in a clear way where is the novelty in the techniques used and their application in this work with respect to other works already carried out ( especially about remote sensing) . Because if there is no clear advance in the state of the art, then this work is a case study and not a research work, so it would not be novel enough to be published in a journal of this level.
What is the objective of advancement in remote sensing techniques regarding the state of the art of this work regarding the techniques that are applied until now? I don't see the progress and novelty clearly
Pag 59-62 In the introduction should also be mentioned about the application of point clouds in the extraction of geometry in different elements and materials (wood, steel, etc.) in the field of building and structures. For example in Timber beam: First results on the combination of laser scanner and drilling resistance tests for the assessment of the geometrical condition of irregular cross-sections of timber beams. Materials and Structures, 51(4), 99. (https://doi.org/10.1617/s11527-018-1225-9). In reinforced concrete: Automatic recognition of common structural elements from point clouds for automated progress monitoring and dimensional quality control in reinforced concrete construction. Remote Sens. 2019, 11, 1102. ( https://doi:10.3390/rs12223702). In steel beam: L. Yang, J.C. Cheng, Q. Wang, Semi-automated generation of parametric BIM for steel structures based on terrestrial laser scanning data, Autom. Constr. 112 (2020), 103037, https://doi.org/10.1016/j.autcon.2019.103037. In railway structures. Self-Organized Model Fitting Method for Railway Structures Monitoring Using LiDAR Point Cloud. Remote Sens. 2020, 12, 3702. (https://doi:10.3390/rs11091102). Etc.
Page 361-362 . For a better understanding of the methodology used and the stages of the work to be carried out in this type of case, it is necessary to make an explanatory flowchart.
Author Response
Thank you very much for your valuable review
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This article is a very interesting case study on 3D reconstruction of a historical site. I found the article interesting to read and although it is somewhat different to the normal content of this journal I feel that it makes a contribution to the field and would be of interest to a proportion of the journal's readership.
Having said that I feel that the main issue with this work is that the authors should consider carefully the audience of the journal that they wish to publish in and adapt their language to meet the audience's needs. Appropriate professional language in one field can easily be opaque or inpenetrable to professionals in a different field. A quick browse of the published articles in Remote Sensing would readily show that the vast majority of articles are written by, and intended for, technologists, not professionals in the cultural heritage field. Indeed, this reviewer falls into that category. As such, references to "Aragonese-style" and the "Angevin" or "Norman-Swabian" periods are not likely to be familar to the audience and might need futher elaboration. Similarly, terminology such as: "structural rationality", "anastylosis" and "standardised seriality" can be expected to be unfamilar to an engineering audience despite the fact that these terms may be well understood and considered common terminology in the author's field. Comments such as "Adeguatio intellectus et rei' was the motto of the Beuronic school." can be expected to have no meaning to a technology-focused audience, and I must confess that as a technologist myself, I could not parse or gain any useful insight from:
"The extraction of components, whether by the direct or indirect method changes little, requires the contextual association of families of technologically determined types stored in dedicated system instructions."
"Placing the punctual survey of the existing at the origin of the workflow at each stage of reconstruction, it will be possible to evaluate the gap between the real form and the normalised form to manage the information [43]."
or
"This explains the choice of placing before the organisation of the design workflow on the existing, a polygonal model, the most suitable for describing the peculiarities of the place in such a way as to make the data considered objective, measured in the comparison, comparable at every stage of the design cooperation."
On a more minor issues, I found that some of the figures need improvement. In particular,
The caption of Figure 5 indicates that a red circle highlights particular areas. I cannot discern a red circle. It appears to either be missing or not sufficiently salient.
Figures 6 and 7 are a low quality and should be replaced by higher quality versions prior to publication.
Author Response
Thank you very much for your valuable review
Author Response File: Author Response.pdf
Reviewer 3 Report
Authors applied photogrammetry and BIM in order to shed light on the structures found in Calabria Region, in a relatively remote and less known medieval site called Oppido Mamrtina (RC,Italy). In their doing so they aimed at documentation of the ruins and better communication to the experts and/or intendants who are responsible from their maintenance.
There are a few points that need to clarified i.e.; how the shadows in the picture were eliminated in figure (2 a); how precise are the 3D models? What are the 3D model measuring error margins? A comparison between in situ measurements (if any) and measurements done on 3D models should be supplied for the column of interest...
The material in the data analysis (section 3.2) paragraph beginning on line 250 and ending on line 268 needs to be more precisely related to the study. Egyptians knew how to disperse load, but how did you include this knowledge into your reconstructions and how does it relate to the 3D models generated by photogrammetry? I think this section (3.2 Data Analysis) should be rewritten accordingly…
I also have a few comments on the document that is attached.
Thank you very much…
Comments for author File: Comments.pdf
Author Response
Thank you very much for your valuable review
Author Response File: Author Response.pdf
Reviewer 4 Report
The article describes the photogrammetric survey of the ruins of the Paolotti convent in the town of Oppido Mamertina (Reggio Calabria, Italy) and investigates the hypothetical reconstruction of the no longer existing elevations and roofs, also through the realisation of a BIM system for documentation purposes.
The paper has some flaws and issues and should not be considered for publication in the Remote Sensing Journal.
- Topic: the paper is not particularly innovative and deals with a generalist description of the processing from the survey to the BIM implementation. The most innovative part concerns the study of the matrices of the vaulted roof and the investigation of the reconstructive hypothesis of the site from the archaeological remains. In the reviewer opinion, these topics are out of the scope of both the Remote Sensing journal and the Special Issue, which searches for articles that “emphasize new perspectives on 3D point cloud acquisition, analysis and postprocessing applied to different fields of research” and “research of high scientific depth regarding the collection and postprocessing of 3D point clouds applied to different fields”.
The part concerning the photogrammetric surveying and post-processing of the point cloud is not innovative. The survey is reduced to a standard image processing performed with Metashape, without any in-depth analysis and with numerous conceptual and methodological flaws. The analysis of the matrices is manual and performed on orthoimages and the modelling is manual as well. No explanation of the modelling methodology is provided and no innovation, compared to the state of the art in recent years, appears.
- Structure of the paper: the structure is lacking and does not allow the reader to immediately understand the focus and the methodology adopted.
The introduction is chaotic, with jumps between references to other works and hints at the topic of the paper. The introduction should be thorough with theoretical references to the previous state of the art, against which the article's objectives and novelty should be highlighted.
The methodology is not immediately evident and should be fully outlined in the first part of the Materials and Methods section.
Many technical and operational aspects are omitted: no information is given on the technical execution of the photogrammetric survey, the realisation of the BIM model, semantic classification, and organisation of information in the database. Many parts appear as statements of intent and general considerations on the usefulness of BIM which, as far as it can be seen, are not confirmed in the work.
Discussions are general and seem like a second introduction with references to other research works. Instead, discussions should be a critical analysis of the work carried out and results obtained, in comparison to the state of the art or to the initial objectives.
- Methodological and conceptual issues: especially the parts concerning the photogrammetric survey have inaccuracies and sometimes lapse into trivialities that should be omitted in a scientific article. To remark a few:
o Lines 52 and 217: why should the point cloud be halved or reduced?
o Section 3.1: no information is given on the photogrammetric survey: block geometry, number of images acquired, images overlap, base-length, distance to the object, number of Ground Control Points (GCPs) (if used), etc.
o Line 139: Why has the ISO been set to 250 when the camera's minimum value is 100? ISO should always be kept as low as possible, especially in high light conditions.
o Lines 144-148: in the reviewer opinion it should be better to omit these considerations.
o Line 165, "alignment". The photogrammetric process is called “Orientation”, “Alingment” is the specific terminology used by the Metashape software.
o Lines 166-168: how was the photogrammetric survey referred to a reference system? Accuracy refers to how close a measurement is to the true or accepted value used as reference and cannot be calculated without comparative data. A survey cannot be said to be accurate without its verification (see line 174).
Furthermore, which LIDAR was used? Which were the resolution and precision of the LIDAR survey? Were they sufficient to constrain the photogrammetric survey or would a topographic survey have been necessary?
The reviewer has some confusion on how the photogrammetric survey has been referenced to the LIDAR point cloud. Were common GCPs (target as said in line 199) used or was a cloud-to-cloud registration performed? If targets were used, why was Polyworks used instead of constraining these targets as GCPs directly in the orientation phase in Metashape?
Moreover, a drone flight generally acquires data in the nadir direction, so vertical elements (in this case the wall ruins) should be the least detected. The photogrammetric survey was instead carried out from the ground with priority acquisition of vertical elements. How was it possible to ensure (and verify) 1 mm standard deviation in the co-registration of the two point clouds? Especially in the presence of vegetation, which introduces a lot of uncertainty in the ground reconstruction.
o Line 171, “different accuracy of the data used”. How much is this accuracy? It has never been calculated.
o Lines 208-211: What 'semantic processing algorithms' were used? Were they used or was semantic classification a manual process? The methodology of the semantic classification process has not been explained, although this topic is even expressed in the title of the paper.
o Lines 364-373: why wasn't the point cloud cleaned before meshing it?
In line 201 it is written that “It was also decided to use the 3D point cloud as basis for the 3D reconstruction to avoid the approximation derived from the meshing algorithms”. In lines 364-370, instead, it is written that “The 'unstructured' model was transcribed into polygonal mesh. Starting from a dense point cloud of more than 106 million points, a mesh of 50 million polygons was created. [….] The 3D mesh (Fig.9a-b) was imported in obj format into the Autodesk Revit 2020 software, dedicated to the informative modelling of artefacts”. The reviewer is confused on the methodology adopted and does not understand why the point cloud was not imported directly into Revit.
o Lines 419-424 and lines 439-441: what information can be obtained from the model? the organisation of the database was not mentioned. The modelling strategy and the maximum deviation between the 3D model and the point cloud were not described. For example, it could have been explained whether loadable families were used (to prioritize elements parameterisation) or whether in-place elements were preferred (to ensure a better fit with the surveyed data) and the reasons for this choice.
- Language: English language and style require extensive editing. In its current form the text is hardly comprehensible. Figure 1 has texts in Italian and 25 out of 54 references are to articles in Italian.
Author Response
Thank you very much for your valuable review
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Accept in present form
Author Response
The authors thank the reviewer for the review
Reviewer 3 Report
Thank you for addressing the concerns stated in the prior review. The additional figures are much better, the language is clearer, and the study's goal can be followed throughout the paper. I believe the manuscript is ready for publication.
Author Response
The authors thank the reviewer fir the review
Reviewer 4 Report
The paper still has several flaws and issues, especially in the part concerning the photogrammetric survey.
The information on the survey is not useful to understand whether the photogrammetric process was successful and what accuracy was obtained. As specified in the previous comments, accuracy refers to how close a measurement is to the true or accepted value used as reference and cannot be calculated without comparative data. Topographically surveyed check points would have been needed to validate the survey.
The GSD may be a good approximation of the expected precision of the survey, not of its accuracy. Similarly, the technical data stated by the LIDAR manufacturer in line 208 (precision of 1 cm and accuracy of 5 cm at 100 m) in no way certify that those are the actual accuracy values. Validation points are needed.
The final accuracy of 1 mm does not seem plausible. There is no information on the resolution (GSD or number of points per square metre) of the LIDAR survey, but it is certain from the data provided by the manufacturer that the density of the LIDAR point cloud is much lower than that obtained from the photogrammetric survey. Therefore, I find it quite strange that co-registration of the photogrammetric survey on a point cloud with an intrinsic uncertainty of 1 cm can give an uncertainty on a distance between points less than 1 mm. The standard deviation value provided by Polyworks at the end of co-registration does not ensure that the entire model has an uncertainty of less than 1 mm. Validation points are needed.
The considerations made in the previous review about introduction and discussion still apply.
As pointed out, the novelty of the paper lies in the extrapolation and in the theoretical analysis and calculus that came from the analysis of the 3D point cloud for an accurate 3D modelling. These topics are rather marginal compared to the normal content of this journal and the audience is more focused on the technical aspects. I believe that the authors need to carefully consider the audience and relevance of the journal, therefore I feel that the issues on the part concerning the survey make the work insufficiently suitable for publication in a journal of the level of Remote Sensing.
I suggest the authors to submit the work to a journal closer to the cultural heritage field.
I'll let the editor decide, possibly avoiding conflict of interest.
Author Response
We thank the reviewer.
The information on the survey is not useful to understand whether the photogrammetric process was successful and what accuracy was obtained. As specified in the previous comments, accuracy refers to how close a measurement is to the true or accepted value used as reference and cannot be calculated without comparative data. Topographically surveyed check points would have been needed to validate the survey.
- we did not have the authorization to put markers on the structure and we did not have the possibility to do a topographic survey
The GSD may be a good approximation of the expected precision of the survey, not of its accuracy. Similarly, the technical data stated by the LIDAR manufacturer in line 208 (precision of 1 cm and accuracy of 5 cm at 100 m) in no way certify that those are the actual accuracy values. Validation points are needed.
The final accuracy of 1 mm does not seem plausible. There is no information on the resolution (GSD or number of points per square metre) of the LIDAR survey, but it is certain from the data provided by the manufacturer that the density of the LIDAR point cloud is much lower than that obtained from the photogrammetric survey. Therefore, I find it quite strange that co-registration of the photogrammetric survey on a point cloud with an intrinsic uncertainty of 1 cm can give an uncertainty on a distance between points less than 1 mm. The standard deviation value provided by Polyworks at the end of co-registration does not ensure that the entire model has an uncertainty of less than 1 mm. Validation points are needed.
- The authors used the DTM but did not acquire the data nor post processed it. The information reported in this paper were given by the company which did the survey. They did not use validation points or markers . We are sorry we did a mistake, it is 1 cm not 1mm. We did add or correct the part but we cannot give information that we do not have.
