A Comprehensive Survey on Short-Distance Localization of UAVs
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsREVIEW OF
A Comprehensive Survey on Relative Localization of UAVs using UWB Sensors
BY
Luka Kramarić, Niko Jelušić, Tomislav Radišić and Mario Muštra
The task formulated by the authors is quite clearly defined by the title. Additionally, the authors write "keeping the literature review comprehensive and up to date is a difficult task." The work is dedicated to this task.
It should be noted that the presentation language is good. It's a bit verbose, but it's not accessible to the most prepared audience. The text can be considered as a popular scientific description of the field of research.
Overall, this is a good overview, although it should be understood that the area chosen is rather narrow. The article can be published, but the authors must bring the text to the state of a full-fledged scientific review. Here are the notes.
1. The title of the review should be substantially revised. First, the abbreviation UWB in the title should be deleted, writing the name in full. But secondly and most importantly, the name should include words that define the limitations of the application (short distance!).
2. Both in the abstract and in the first lines of the introduction, the authors should make it very clear to the reader that the localization task is of a limited application nature, specifying target or limit distances, indoor navigation, and navigation inside the swarm.
3. Authors should specify their ORCIDS. The reader should be able to quickly and easily familiarize himself with the authors' works, including getting an idea of their research competencies and the authors' grounds for writing a review.
4. By default, the typical lower bound for writing a review is the number 100. This is the minimum to require a review. In a regular article, as a rule, up to 50 references are indicated in the review part. The authors should supplement the references, possibly with works from less high-level sources. In general, the approach to citation chosen by the authors looks unacceptably minimalistic. Here is a typical example of "It is a relatively new technology in the field of localization and navigation which was initially developed for high data-rate communication". If the reviewer had written such an article, the first issue would be the search for primary sources, the first works in which this (the main one for the review) technology was presented. And the place of these references is here and immediately, and not in the arguments below. Why do the authors in the review save numbers for references?
5. The abstract is written incorrectly. The text of the abstract should be included in the introduction. In the abstract, it should be written in simple, concise and extremely formal language: An overview is presented ... in the field ... The overview and analysis are structured … This is done for the purpose of …
6. From a mathematical point of view, the localization problem under consideration is a nonlinear filtering problem. The authors, in fact, limit themselves to one or two phrases, for example, "the most often used method is the Kalman filter" (line 307). Of course, that's not what it's about. The reviewer does not dispute that the technical side of the problem, in particular, sensors, is the most important issue. But the method of calculating the score, the filter, is also an important part. For example, the question arises – since you use the Kalman filter, the surveillance system is linear. What makes the UAV fly according to a linear law, why are range measurements linear? etc. The second phrase, "Most of the studies mentioned in this section implement the extended Kalman filter (EKF)", will somewhat clarify the story of linear systems. But EKF is the simplest nonlinear filter, invented more than 70 years ago. This is all? There are many such questions that can be asked. There are no answers to them in this review, not even close. Accordingly, the authors are required either to supplement the review with an overview of the filtering methods used, or to indicate in the first lines that the mathematical side of the localization process is beyond the scope of the review. Then it is better to remove the mention of filters from the text, because neither the wonderful (really wonderful) Kalman filter (plus the extended one), nor the casually mentioned uncented filter, reflect even 10% of the methods used in the field.
7. A good overview of the performed and published experiments in section 3 of the article means, among other things, that almost no mathematical methods were used to solve the problem. Everything is limited by typical "old" methods and algorithms, and no modern advances in the field of nonlinear filtering have reached the subject of the article. This is a challenge that the authors don't write about! Many of the problems that have manifested themselves in experiments and real data can be solved not by more complex and "smart" sensors, but by more "smart" filters! There is no special claim to the authors, this is not their topic. But they should clearly state that the integration of heterogeneous information and the assessment of the UAV position based on indirect measurements is not the topic of the article at all.
Author Response
Comment: The task formulated by the authors is quite clearly defined by the title. Additionally, the authors write "keeping the literature review comprehensive and up to date is a difficult task." The work is dedicated to this task.
Response: Thank you for the comment, the sentence: ”Secondly, the rapidly evolving nature of UAV technology and localization methods, followed by an increasingly large number of published papers, means that keeping the literature review comprehensive and up to date is a difficult task.” is rephased to: “Secondly, the rapidly evolving nature of UAV technology and localization methods, followed by an increasingly large number of published papers, makes choosing the adequate papers as the information source rather challenging.”
Comment: It should be noted that the presentation language is good. It's a bit verbose, but it's not accessible to the most prepared audience. The text can be considered as a popular scientific description of the field of research.
Response: Thank you for the comment, we tried to further improve writing, polish some sentences out and correct occasional misused tenses.
Comment: Overall, this is a good overview, although it should be understood that the area chosen is rather narrow. The article can be published, but the authors must bring the text to the state of a full-fledged scientific review. Here are the notes.
Response: Thank you for the comment, we will address each note individually.
Comment: 1. The title of the review should be substantially revised. First, the abbreviation UWB in the title should be deleted, writing the name in full. But secondly and most importantly, the name should include words that define the limitations of the application (short distance!).
Response: Thank you for the idea, our choice of „UWB“ was to avoid a long title. The short distance seems appropriate. The title is changed to „A Comprehensive Survey on Short-Distance Localization of UAVs“. We kept one abbreviation, but it is of a wider-known term. Another option is to replace UAVs with Drones.
Comment: 2. Both in the abstract and in the first lines of the introduction, the authors should make it very clear to the reader that the localization task is of a limited application nature, specifying target or limit distances, indoor navigation, and navigation inside the swarm.
Response: Thank you for the comment, we included the following:
“This paper gives a comprehensive overview of short-distance localization methods for UAVs, exploring their strengths, limitations, and practical applications.”
“By highlighting the current trends in UWB-related research, including its increasing use in swarm control, indoor navigation, and autonomous landing, potential researchers a could use it as a guide for choosing the appropriate localization techniques, emphasizing UWB's potential as a foundational technology in advanced UAV applications.”
“One of focuses of this paper is to explore the state-of-the-art in relative localization of UAVs in swarms, which needs to fulfill the required positioning accuracy.”
“This comprehensive analysis is intended to assist researchers, developers, and industry professionals in making informed decisions about the best short-distance localization technologies for their specific UAV applications.”
Comment: 3. Authors should specify their ORCIDS. The reader should be able to quickly and easily familiarize himself with the authors' works, including getting an idea of their research competencies and the authors' grounds for writing a review.
Response: Thank you, it should be fine now and all the authors should be visible through ORCID.
Comment: 4. By default, the typical lower bound for writing a review is the number 100. This is the minimum to require a review. In a regular article, as a rule, up to 50 references are indicated in the review part. The authors should supplement the references, possibly with works from less high-level sources. In general, the approach to citation chosen by the authors looks unacceptably minimalistic. Here is a typical example of "It is a relatively new technology in the field of localization and navigation which was initially developed for high data-rate communication". If the reviewer had written such an article, the first issue would be the search for primary sources, the first works in which this (the main one for the review) technology was presented. And the place of these references is here and immediately, and not in the arguments below. Why do the authors in the review save numbers for references?
Response: Thank you for the comment. You are correct to notice a rather limited number of references for a review article. The reasons for that are in the time-limitation we have tried to apply, and that is to review the research within the last 5 years. Since our mission was to explore RF-based methods, mostly UWB, the number of papers is rather limited. We have tried to include the accessible papers with, at least, sound methodology that we thought could be of benefit to the community. Another limitation was the length of the manuscript, which we tried to keep around 25 pages, to comply with the trends of reducing the page count as much as possible.
In the revised version we added a new section dedicated to data fusion.
We have included additional references which we think are a valuable contribution to the topic, especially in section 5, and the total number now is 102, which made the paper a bit longer, 29 pages.
Comment: 5. The abstract is written incorrectly. The text of the abstract should be included in the introduction. In the abstract, it should be written in simple, concise and extremely formal language: An overview is presented ... in the field ... The overview and analysis are structured … This is done for the purpose of …
Response: Thank you for the comment. We have rewritten the abstract in the more formal and passive form. The modified and shortened abstract is: “The localization of Unmanned Aerial Vehicles (UAVs) is a critical area of research, particularly in applications requiring high accuracy and reliability in GPS-denied environments. This paper presents a comprehensive overview of short-distance localization methods for UAVs, exploring their strengths, limitations, and practical applications. Among short-distance localization methods, Ultra-Wideband (UWB) has gained significant attention due to its ability to provide accurate positioning, resistance to multipath interference, and low power consumption. Different approaches to usage of UWB sensors, such as the Time of Arrival (ToA), the Time Difference of Arrival (TDoA), and the Double-Sided Two-Way Ranging (DS-TWR), alongside their integration with complementary sensors like Inertial Measurement Units (IMUs), cameras, and visual odometry systems are explored. Furthermore, the paper provides evaluation of the key factors affecting UWB performance, including anchor placement, synchronization, and the challenges of combined use with other localization technologies. By highlighting the current trends in UWB-related research, including its increasing use in swarm control, indoor navigation, and autonomous landing, potential researchers could benefit from it as a guide for choosing the appropriate localization techniques, emphasizing UWB's potential as a foundational technology in advanced UAV applications.
Comment: 6. From a mathematical point of view, the localization problem under consideration is a nonlinear filtering problem. The authors, in fact, limit themselves to one or two phrases, for example, "the most often used method is the Kalman filter" (line 307). Of course, that's not what it's about. The reviewer does not dispute that the technical side of the problem, in particular, sensors, is the most important issue. But the method of calculating the score, the filter, is also an important part. For example, the question arises – since you use the Kalman filter, the surveillance system is linear. What makes the UAV fly according to a linear law, why are range measurements linear? etc. The second phrase, "Most of the studies mentioned in this section implement the extended Kalman filter (EKF)", will somewhat clarify the story of linear systems. But EKF is the simplest nonlinear filter, invented more than 70 years ago. This is all? There are many such questions that can be asked. There are no answers to them in this review, not even close. Accordingly, the authors are required either to supplement the review with an overview of the filtering methods used, or to indicate in the first lines that the mathematical side of the localization process is beyond the scope of the review. Then it is better to remove the mention of filters from the text, because neither the wonderful (really wonderful) Kalman filter (plus the extended one), nor the casually mentioned uncented filter, reflect even 10% of the methods used in the field.
Response: Thank you for the comment. We agree that not enough depth was put into nonlinear filtering for state estimation. The reason for heavy usage of the (E)KF is because it is implemented in most of-the-shelf flight-controllers for the fusion of sensor data, so the research community heavily relies on it. We have added a section dedicated to data fusion (3.1) and provided further 12 references from that field, which might be of interest to a potential reader.
Comment: 7. A good overview of the performed and published experiments in section 3 of the article means, among other things, that almost no mathematical methods were used to solve the problem. Everything is limited by typical "old" methods and algorithms, and no modern advances in the field of nonlinear filtering have reached the subject of the article. This is a challenge that the authors don't write about! Many of the problems that have manifested themselves in experiments and real data can be solved not by more complex and "smart" sensors, but by more "smart" filters! There is no special claim to the authors, this is not their topic. But they should clearly state that the integration of heterogeneous information and the assessment of the UAV position based on indirect measurements is not the topic of the article at all.
Response: That is correct, we focused mainly on sensors in the original manuscript. In the revised version we included a sub-section dedicated to state estimation and provided further reference with the statement that this topic will not be substantially covered in this paper. We referred to suitable papers, including review papers from the field, dealing with state estimation and fusion of sensory data, that are novel and cover state-of-the-art. Our focus was kept to the usage of the ToF or the TDoA approaches with which researchers try to achieve sensible tracking of a single UAV or small swarms of UAVs. They usually integrate UWB as an additional sensor and try to modify the flight controller’s output by adding additional data and modeling it to work correctly with the IMU data. We have added a more thorough explanation of the subject discussed in the paper.
The structure of sections is slightly modified to improve readability.
All the significant changes, except small language-related changes, are highlighted in red to differentiate from the originally submitted version.
Reviewer 2 Report
Comments and Suggestions for Authors1. The writing logic of the manuscript needs to be adjusted. It is recommended to sort out the levels from the original measurement of UWB to data processing and then to the application.
2. The main text seems to be a list of literature. The documents should be summarized and concluded instead of just explaining what the literature did.
3. It is recommended to add a structural block diagram to make it easier for readers to understand the ideas of the article.
4. It is recommended to give some brief introduction to the source of the literature.
5. The length of Background and Fundamentals is too long. It is recommended to compress it to 1 to 2 pages. Since the title has clearly stated UWB and UAV, it is necessary to explain these two topics, and there is no need to talk about all other sensors, especially visual sensors.
6. Some descriptions of visual positioning need to be considered, and a unified representation method should be used. For example, in the positioning technology in Section 2.3, it is incorrect to divide the visual positioning methods into stereo vision, monocular vision and optical flow. The first two are the number of sensors, and the latter is the processing method, which cannot appear in the same classification.
7. The appearance of formula (3) is rather abrupt and needs to be preceded by a guide.
8. Each paragraph in the subsequent chapters is very long and can be divided into paragraphs according to the topic.
9. The conclusion is not intuitive enough. The potential research directions (1), (2) and (3) should be explained one by one to reflect the research value of this article.
Author Response
Comment: 1. The writing logic of the manuscript needs to be adjusted. It is recommended to sort out the levels from the original measurement of UWB to data processing and then to the application.
Response: Thank you for the comment. With regards to this and other reviews, we have made changes to the structure of the manuscript and changed the title to avoid less-common abbreviation and give emphasis to the short-distance localization. Larger changes are colored red in the ravised version to make better differentiation to the originally submitted version.
Comment: 2. The main text seems to be a list of literature. The documents should be summarized and concluded instead of just explaining what the literature did.
Response: Thank you, we have split the manuscript to provide a potential reader with more insights into different fields we tried to address. The structure is now significantly different and, hopefully, easier to follow.
Comment: 3. It is recommended to add a structural block diagram to make it easier for readers to understand the ideas of the article.
Response: Thank you for the idea. We included a block diagram representing the topics covered in the paper at the end of Introduction.
Comment: 4. It is recommended to give some brief introduction to the source of the literature.
Response: Thank you, we included the following sentence in the Introduction: “The main literature sources are papers published within the 5 years at the moment of writing with a good citation record, as well as some older papers, covering the basic principles of certain mentioned methods.“ This was also mentioned in the conclusions.
Comment: 5. The length of Background and Fundamentals is too long. It is recommended to compress it to 1 to 2 pages. Since the title has clearly stated UWB and UAV, it is necessary to explain these two topics, and there is no need to talk about all other sensors, especially visual sensors.
Response: Thank you, we reduced the part covering fundamentals of visual sensors, especially LiDARs. Section 2 is now “Overview of the requirements for UAVs and sensors”, and requirements for UAVs are covered in 2.1. In Section 3 we added a section regarding data fusion and state estimation, which, we hope, will be of benefit to readers who are more interested in automation and control field. Section 4 covers the UWB fundamentals and requirements for UAVs are covered in 2.1.
Comment: 6. Some descriptions of visual positioning need to be considered, and a unified representation method should be used. For example, in the positioning technology in Section 2.3, it is incorrect to divide the visual positioning methods into stereo vision, monocular vision and optical flow. The first two are the number of sensors, and the latter is the processing method, which cannot appear in the same classification.
Response: Thank you, that is absolutely correct. We have rephrased the text to: “Visual localization relies on cameras and other optical sensors to acquire information about the environment and produce distance measurements. There are different methods in terms of the type and number of used sensors and processing methods.“ We have moved the optical flow to a new paragraph and gave a more clear distinction with the following: “Besides estimation of the position based on analysis of still images and pairs of images, a mention-worthy approach is the optical flow which estimates the motion of objects in an environment based on sequential images captured by the same camera.“
Comment: 7. The appearance of formula (3) is rather abrupt and needs to be preceded by a guide.
Response: Thank you, the problem partially was in the description of the time measurement process being visually separated from the formula itself. We rephrased the explanation to: “The time of flight tof (3) used as a parameter to measure the distance from a UAV to each anchor is calculated using the specific times from sending a poll message to receiving a report, shown in Figure 3.“ Besides that, there was a mistake propagated from the cited paper, which is now corrected.
Comment: 8. Each paragraph in the subsequent chapters is very long and can be divided into paragraphs according to the topic.
Response: Thank you for the comment, we have split Section 2 into two sections with the goal of improving readability. Also, we have introduced further splits of, currently, the largest Section 4 and section 5.
Comment: 9. The conclusion is not intuitive enough. The potential research directions (1), (2) and (3) should be explained one by one to reflect the research value of this article.
Response: Thank you for the comment. We have thoroughly rewritten the conclusion dividing it into logical units trying to answer questions about why to choose a certain combination of sensors, which distance measurement method to use, and what is the expected accuracy of the system regarding the currently available technology. The conclusions are now split into paragraphs dedicated to: the structure of the paper and description of the literature source, used distance measurement methods, used hardware, sensory data fusion, application in swarm control, and current situation regarding the obtainable accuracy in short distance localization.
Reviewer 3 Report
Comments and Suggestions for AuthorsDear authors,
I reviewed with interest your comprehensive paper on UAV relative positioning.
I think it is generally well written, but there are some questions and some areas should be revised.
Please respond to the following questions and comments.
sincerely yours,
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1) There are too few line breaks in this paper, making it very difficult to read. You should add line breaks appropriately.
2) In many cases, abbreviations are written without the full abbreviation before them. The first time the abbreviation appears in a sentence, the full abbreviation should be written immediately before it. At the very least, you should inform the reader at the beginning of the paper that a list of abbreviations is provided at the end of the paper.
3) 24/7 is a very colloquial expression and should be changed to something more appropriate for use in a sentence.
4) The chapter titles are easy to understand because they are written in large letters and separated by blank lines, on the other hand, the font of the section titles is the same font and size as the main text, making it difficult to understand. (The italic font actually makes it smaller than the font size in the main text.)
Also, the line spacing between sections is the same as that of the main text, making it difficult to distinguish between sections.
Please make the font of the section titles a little larger and emphasized to make them easier to distinguish.
5) Some section titles are not italicized. Please make this consistent.
6) The explanation of equation (1) is insufficient and I don't understand it. What does s(t - τ) represent?
7) (xm, yn) on line 296 is incorrect. The correct word should be (xm, ym).
8) What is the Vicon system on line 471? If it is not a commonly known term, an explanation should be included.
9) Shouldn't Figure 4 on line 564 be Figure 5?
10) The numerator on the right-hand side of equation (3) is incorrect. I think the correct answer is (trr - tsp)(trf - tsp) - (tsf - trr)(tsr - trp).
11) I think the meaning of "ground truth" used in this paper is different from the general meaning of the word. What does "ground truth" mean in this paper? Also, if the meaning is used only in this paper, it should be explained beforehand.
12) From line 585 to line 587, the expression "depth of the room" is used, but I think the expression "height of the room" would be easier to understand.
13) In the text explaining the figure, the number of the figure is written at the end of the text, which is difficult to understand. For example, I think it would be better to write "in Figure xx," at the beginning of the text explaining the figure.
Comments on the Quality of English LanguageSome comments on English expressions are included in "the Comments and Suggestions for Authors", so please refer to that.
Author Response
Dear authors,
I reviewed with interest your comprehensive paper on UAV relative positioning.
I think it is generally well written, but there are some questions and some areas should be revised.
Please respond to the following questions and comments.
sincerely yours,
Thank you for your time and effort, we will address each individual comment below.
Comment: 1) There are too few line breaks in this paper, making it very difficult to read. You should add line breaks appropriately.
Response: Thank you for the comment, we have made a significant change in the layout, split section 2 and created separate paragraphs throughout the sections. Conclusion is also divided into paragraphs to achieve a visual division of topics which the paper tried to cover. Line breaks are now placed to distinguish between papers which are not closely related in their scope.
Comment: 2) In many cases, abbreviations are written without the full abbreviation before them. The first time the abbreviation appears in a sentence, the full abbreviation should be written immediately before it. At the very least, you should inform the reader at the beginning of the paper that a list of abbreviations is provided at the end of the paper.
Response: Thank you, we added full names of abbreviated methods or sensors upon the first mention in the text and gave alphabetically sorted list at the end, as per the MDPI template.
Comment: 3) 24/7 is a very colloquial expression and should be changed to something more appropriate for use in a sentence.
Response: Thank you, we used the term “continuous“ instead of 24/7 in the revised version.
Comment: 4) The chapter titles are easy to understand because they are written in large letters and separated by blank lines, on the other hand, the font of the section titles is the same font and size as the main text, making it difficult to understand. (The italic font actually makes it smaller than the font size in the main text.)
Also, the line spacing between sections is the same as that of the main text, making it difficult to distinguish between sections.
Please make the font of the section titles a little larger and emphasized to make them easier to distinguish.
Response: Thank you, we used the official template for MDPI Drones which defines styles for each element. However, we made a mistake in the format of the title of sub-sub-section which is of the same letter size as the text (Palatino Linotype 10) but should have 3 pt before and after spacing. We added spacing to all instances.
Comment: 5) Some section titles are not italicized. Please make this consistent.
Response: Thank you, as per the official template, the sub-sub-sections (number format x.y.z.) are not defined to be in italic but is now a bit visually better with added spacings.
Comment: 6) The explanation of equation (1) is insufficient and I don't understand it. What does s(t - τ) represent?
Response: Thank you for the comment. We have provided a more explanation of the equation and noticed that the reference linked to it was wrongly placed. The correct paper (technical report) is now linked to it. The idea was to introduce readers with the varying (broadband) channel properties, which is a more significant problem in UWB because of the non-linear transmission function.
s(t - τ) represents the signal at the receiver (after the required time τ during which it covers the distance between the transmitter and receiver) and is multiplied by the channel coefficient and influenced by noise.
Comment: 7) (xm, yn) on line 296 is incorrect. The correct word should be (xm, ym).
Response: Thank you for noticing. It was a copy-paste mistake while writing the equation. We have corrected it.
Comment: 8) What is the Vicon system on line 471? If it is not a commonly known term, an explanation should be included.
Response: Thank you for a good input, we rephrased the sentence to: “The authors used the Vicon Vero 2.2 motion capture system for ground truth and bound the maximum 3D localization error to 28 cm.“
Comment: 9) Shouldn't Figure 4 on line 564 be Figure 5?
Response: Thank you, that is correct. In the revised version there are couple of more figures added, so this became figure 8.
Comment: 10) The numerator on the right-hand side of equation (3) is incorrect. I think the correct answer is (trr - tsp)(trf - tsp) - (tsf - trr)(tsr - trp).
Response: Thank you for noticing.
Unfortunately, it is the case of a wrong equation in the cited paper. The idea of DS-TWR should be ((Tround1*Tround2)-(Treply1*Treply2))/(Tround1+Tround2+Treply1+Treply2), which equals to: (trr-tsp )(trf-tsr )-(tsf-trr )(tsr-trp). We kept the same reference believing that it was an unintentional mistake by the authors and it provides a good graphical reference.
Comment: 11) I think the meaning of "ground truth" used in this paper is different from the general meaning of the word. What does "ground truth" mean in this paper? Also, if the meaning is used only in this paper, it should be explained beforehand.
Response: Thank you for noticing. The ground truth is in this paper considered to be the best possible way of measuring the position (usually by motion capture systems) or knowledge of the exact position versus the boundaries of the testing facility. There were some unclear usages of the term and we have made the following changes of the usage: “The authors used the Vicon Vero 2.2 motion capture system which produced locations of UAVs as ground truth and bound the maximum 3D localization error to 28 cm.“
„Using the TWR for distance measurements and motion capture system results as the ground truth authors obtained an average positioning error of 67 cm in 3D.“
„The authors used a public dataset for VIO and since the set did not contain UWB measurements, they added the distances from target to anchors with Gaussian noise with standard deviation σ to each individual distance and concluded that adding UWB improves the performance of global pose estimation significantly.“
„Using the TWR for distance measurements and motion capture system to provide the ground truth authors obtained an average positioning error of 67 cm in 3D.“
Comment: 12) From line 585 to line 587, the expression "depth of the room" is used, but I think the expression "height of the room" would be easier to understand.
Response: Thank you, the sentence was difficult to understand because it was not written properly. It was rewritten to: “In rooms which have square-shaped floor plans, the best option is to place the anchors in 4 corners of the room while for rectangular rooms, where one dimension is significantly larger, it is better to have anchor(s) placed closer to the center of the room.“
Comment: 13) In the text explaining the figure, the number of the figure is written at the end of the text, which is difficult to understand. For example, I think it would be better to write "in Figure xx," at the beginning of the text explaining the figure.
Response: Thank you for the comment. We have changed the word order in sentences accordingly in all the places where it was applicable and possible.
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe revised manuscript has been substantially revised from the first version, with additional documentation, restructuring, and a significant improvement in quality.
1. There are many abbreviations, but the writing style needs to be standardized. Whether the first letter is capitalized or not should be consistent, such as Extended Kalman filter (EKF), Unscented Kalman Filter (UKF), etc. Abbreviations in the summary need not be fully capitalized again.
2. References should be written in a standardized manner, e.g., Literature 22 on line 264, Literature 32 on line 309.
Author Response
Comment: The revised manuscript has been substantially revised from the first version, with additional documentation, restructuring, and a significant improvement in quality.
Response: Thank you. We will make the changes according to the comments and recheck the manuscript.
Comment: 1. There are many abbreviations, but the writing style needs to be standardized. Whether the first letter is capitalized or not should be consistent, such as Extended Kalman filter (EKF), Unscented Kalman Filter (UKF), etc. Abbreviations in the summary need not be fully capitalized again.
Response: Thank you, we agree with the suggestion and have rechecked the manuscript to make usage of capitalization standardized throughout.
Comment: 2. References should be written in a standardized manner, e.g., Literature 22 on line 264, Literature 32 on line 309.
Thank you. If we understood correctly, the suggestion is to include the author’(s) name(s) when referring to the cited work. Since this format includes numbers, we have included names where it was possible, due to the sentence structure and to avoid repeating the same sentence construct. This was done mainly to make the reading more fluent.
