Positional Accuracy Assessment of Digital Orthophoto Based on UAV Images: An Experience on an Archaeological Area

Round 1

Reviewer 1 Report

The paper is interesting. I have few comments:

1. can the authors compare their results against other methods?
2. An algorithm would be better for understanding the method.
3. The acquisition process and analysis are not clear. They should be better presented.

Add only an algorithm describing the method in terms of inputs and outputs and also define the free parameters of the model.

Author Response

Dear Reviewer,

Thank you for valuable contributions to our paper.

You can find our reply to your each comments in the attachment.

Best Regards.

Author Response File: Author Response.docx

Reviewer 2 Report

Thanks for the opportunity to read this paper.

In my opinion the project is very interesting because it contributes to the generation of planimetric documentation in archaeological sites using UAV considering the accuracy requirements necessary for this type of work.

However, the manuscript is not yet ready for publication, but has much promise if the authors are willing to undertake some revisions:

Line #183. The location of the palace should be defined using the geographic position (latitude and longitude), in addition to Figures 1, 2 and 3 should be structured as a map: Coordinates in the margins, position of Geographic North and Approximate Scale.

None of these three figures are referenced in the text.  They should be referenced.

Lines 212-220. A detailed description of the characteristics of the building is made, I suppose referring to the detail map (figure 3), this figure does not help to interpret the text and furthermore it is not referred to. It should be improved by using the orthophoto generated with a higher level of detail.

Lines 222-230. A description is made of the types of decoration that exist in the building. It should be accompanied by images to help in its interpretation.

Line 237. In section 3.1.- Methodology. Only a flow diagram of the different stages is shown without any explanation (Figure 4): some explanatory text of the complete workflow of the photogrammetric process should be included, from data capture to obtaining the final products.

Line #241. Section 3.2.UAV Flight. A description of the drone to be used is given, but no details are given of the flight plan planned for the execution of the project: software used for its design, flight orientation, flight height according to the GSD of the project, longitudinal and transversal overlaps, capture speed, flight time, etc. This design is previous to the capture and will condition the design of the photocontrol points network and, given the flight objectives (to evaluate the accuracy), the design of the check points network.

Line #350. Section 3.3. Ground Control Points (GCP) and Data Collection This paragraph describes in detail how the flight has been executed,  but does not compare with the designed flight. In addition, it should also detail the location of the photocontrol and check points, the criteria for the number of points needed, their location, the accuracy achieved, etc. The explanation of the two flights captured is not clear.

Line #254. The authors explain: Image alignment was carried out with 373 cameras, on the other hand in table 2, it is explained that 903 images have been captured and 859 have been aligned: please explain the difference. Moreover, it is not detailed what was the capture time and the camera orientation (vertical or another angle). Could you please justify why the transverse overlap is higher (80%) than the longitudinal overlap (60%).

Figures 13 and 14. Since the product is an orthophoto (map) it should have a coordinate grid or a graphic scale and the direction of North.

In section 4.1.- Specific Requirements. The number of points needed to perform the accuracy control using the methodology proposed by ASPRS Accuracy Standards for Digital Spatial Data is detailed in lines #359-380. The authors have made a very detailed description of the number of points needed for both horizontal and vertical accuracy control. After applying them to the conditions of the article, the authors conclude that 14 GCP will be used without making a justification related to the methodology. Could they explain this on more detailed and justify why there are only 14?

Additionally, the ASPRS methodology makes it clear that the Check points cannot be the same as the GCPs used in the photogrammetric process. As it appears from reading the paper, the same control points used for the TA have been used as check points. This means that the accuracy results are going to be much more optimistic than the reality and that the method is not being applied properly.

In line #493, section 5. Results, it is duplicated. I guess it should be Conclusions. Please correct it.

Author Response

Dear Reviewer,

Thank you very much for your valuable contributions to our paper.

You can find our reply to your each comment in the attachment.

Best Regards.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors have taken into account all my suggestions.

The manuscript is adequate to published

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.