Optimization of Ground Control Point Distribution for Unmanned Aerial Vehicle Photogrammetry for Inaccessible Fields

Round 1

Reviewer 1 Report

GCP is necessary for image georeferencing. This article presents methods that can deal with fields inaccessible for GCP placement. However, ① high precision POS based georeferencing methods is gradually taking the place of GCP so that no GCP or less GCP is needed during remote sensing flight. ② the topic is about inaccessible field, however, flat farmland is used to validate your methods. As we all agree, inaccessible areas are mostly mountainous. Have you ever taken the ground shape into consideration? ③ the method you propose can not only deal with areas inaccessible, but also can reduce the needs of GCP as I see from you result that less GCP is needed for the correction. ④ The errors are nonnegligible. The result can’t convince me that the methods is effective. As we know, the CEP of RTK GPS is usually at 3~5cm. ⑤I’m confused why you submit this paper to sustainability? Does this research have anything related to the scope of this journal? Why you don’t submit to journals like remote sensing, or other remote sensing related journals?⑥what’s the points of placing low R2  figures?

In summary, the novelty, advancement and significance of this research is lack of proof. 

 

Author Response

Dear Reviewer,

Thank you very much for reviewing the manuscript and making the precious comments. We made our responses in a word file. 

Please kindly see the attachment. 

Thank you. 

Author Response File: Author Response.pdf

Reviewer 2 Report

The content of the article is consistent with the scientific area of the Journal. The subject raised by the authors is current and so far rarely noticed by other authors publishing in this area.

The paper has an original, scientific character: for a better clarification, please edit your paper as follows:

1. Enlarge the Introduction with current results reported in the world and Europe
2. define better the scientific results
3. Improve the reference list

Author Response

Dear Reviewer,

Thank you very much for reviewing the manuscript and making the precious comments. We made our responses in a word file. 

Please kindly see the attachment. 

Thank you. 

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscript is dedicated to the important problem of increasing the accuracy of sounding using UAVs. The authors conducted a wide series of experimental surveys to confirm their findings. The manuscript may be published.

The literature review could have been done more broadly e.g. recent article: https://doi.org/10.3390/app12094598

Author Response

Dear Reviewer,

Thank you very much for reviewing the manuscript and making the precious comments. We made our responses in a word file. 

Please kindly see the attachment. 

Thank you. 

Author Response File: Author Response.docx

Reviewer 4 Report

Paper: Optimization of Ground Control Point Distribution for Un- 2 manned Aerial Vehicle Photogrammetry for Inaccessible Fields

Minor comments:

1. The introduction of this paper must be revised. The revision of the state of the art must be enriched with additional references, by including its critical analysis.

2. This paper uses a lot of acronyms. It will be useful to include into a list to make easy the readability of the paper.

3. Data in Figure 8 is not readable, revise its size.

Recommendation:

The paper is valuable for the research community. The experimental validation and analysis are well developed and presented by the authors.

Author Response

Dear Reviewer,

Thank you very much for reviewing the manuscript and making the precious comments. We made our responses in a word file. 

Please kindly see the attachment. 

Thank you. 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I’m personally not favor of this topic as GCP is a standard process and there are direct georeferencing methods which can be used for area where can’t place GCP marks. However, this research presents a new idea and the research is complete regardless of its practicability. Then I have several comments/advice for authors: 1. L39, UAV related articles are advised as below a) Forests growth monitoring based on tree canopy 3D reconstruction using UAV aerial photogrammetry[J]. Forests b) Two-step ResUp&Down generative adversarial network to reconstruct multispectral image from aerial RGB image c) Fusion of multispectral aerial imagery and vegetation indices for machine learning-based ground classification d) High-Temporal-Resolution Forest Growth Monitoring Based on Segmented 3D Canopy Surface from UAV Aerial Photogrammetry 2. L133, the current study->this study 3. L142-147, too detailed description of the study area. It’s advised to briefly explain why this site was selected for study. 4. L182, there is standard mark format for equipment used in study, like Inspire2(DJI Inc, Shenzhen, China). So are the other products/software in the manuscript. 5. L196, inputting? 6. L204-206, it’s advised to rewrite this sentence. It’s confusing. 7. Figure 5. This figure is quite confusing. Why you place a fitting line on the figure while the fitting accuracy is so low? 8. L446, the optimal doesn’t need most. 9. Figure 10. Why there are two * behind R? Moreover, the correlation coefficient is incredibly low. 10. L456, not only----but also. Too much grammatical errors. 11. L458-460, it is arrogant. GCP is standard method to guarantee the aerial images are precisely georeferenced. You just want to trade off its accuracy for convenience. I can’t see evidence your methods are equally or acceptably as accurate as GCP. Moreover, there is other methods like POS based method which have proven very effective and less labor involved. 12. Have you ever considered if the survey areas are completely mountainous or covered with forest that are impossible for any GCP placement? How will this method be used? I advise you rewrite this manuscript to meet the standard of academic papers. Pay special attention to language and narrative tone. This article can’t represent the advancement of georeferencing but a possible solution to extend the use of GCP. And the conclusion isn’t very soundly supported by the results.

Author Response

Dear Reviewer, 

Thank you again so much for spending your time reviewing the manuscript. 

We have made our response to your comments in the word file attached. 

Please kindly check it. 

Our best regards, 

Authors

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

Congratulations

Author Response

Dear reviewer, 

We appreciate your comments and help so far. 

Thank you so much.