Assessment of New Techniques for Measuring Volume in Large Wood Chip Piles

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Relevance of the Topic

The topic is relevant to the field of precision forestry, which is becoming increasingly important in forest management, biomass production, and sustainability. The paper addresses a significant operational challenge: accurately estimating the volume of wood chip piles, which is crucial for industries involved in biomass energy production. The comparison of various modern technologies (laser scanning, UAV, LiDAR) with traditional methods ensures its relevance across both academic research and practical forestry operations.

The innovation in the paper lies in the direct comparison of multiple techniques for volume estimation, including advanced methods like UAVs, terrestrial laser scanning (TLS), and smartphone-based LiDAR. The discussion of trade-offs in terms of accuracy, time, and cost adds practical value. The inclusion of smartphone-based LiDAR technology (e.g., iPhone 15 Pro Max) is particularly novel and opens new possibilities for low-cost field applications.

Suitability of Data Collection and Analysis

I prefer not to comment on the suitability of data collection methods, as I have never used the mentioned equipment. Therefore, I do not feel equipped to adequately assess the suitability of the data collection methods presented.

Regarding the analysis methods, using software such as 3D Survey and Agisoft for point cloud processing is appropriate and ensures precision in the results. The author has well-structured the volume calculation section by categorizing the methods according to the nature and quality of the input data, including manual tape measurements, point-based calculations (GPS and Vertex), and point cloud-based calculations (UAV, TLS, HMLS, and iPhone).

Results and Discussion

The results are presented clearly, and the comparison of techniques provides valuable insights into their practical applications. The radar chart (Figure 14) for comparing price, time, accuracy, and difficulty is particularly effective in helping readers visualize the trade-offs. The discussion section provides a strong reflection on how the different methods performed and which ones are better suited for different operational contexts. The emphasis on the time and economic efficiency of UAVs and smartphones aligns well with the industry's need for cost-effective solutions.

However,

The authors should consider providing a true reference value for the wood chip pile’s volume to strengthen the validity of their comparisons. Without a reference, the current results are based on relative comparisons, making it difficult to definitively assess the accuracy of each method. While the authors claim that TLS is the most accurate based on its technical characteristics, this assertion would benefit from validation against a known reference volume or ground truth.

If obtaining a reference value is not feasible due to operational constraints, the authors could explicitly address this limitation and explore alternative validation methods. These could include using simulated or controlled environments where volume estimates from TLS and other methods could be compared more rigorously. Such an approach would provide stronger empirical support for their claim regarding the superior accuracy of TLS.

Additionally, the authors should suggest data collection methods aimed at improving the accuracy of volume estimation with the iPhone, given its advantages in terms of low cost, reduced processing time, and ease of use. By exploring methodological adjustments or combining it with other technologies, it could be possible to maximize the potential of this technology to provide more accurate volume estimates while maintaining its operational benefits.

Author Response

If obtaining a reference value is not feasible due to operational constraints, the authors could explicitly address this limitation and explore alternative validation methods. These could include using simulated or controlled environments where volume estimates from TLS and other methods could be compared more rigorously. Such an approach would provide stronger empirical support for their claim regarding the superior accuracy of TLS.

We agree the reference volume has been added based on the company's woodchips pile volume data evidence.

Additionally, the authors should suggest data collection methods aimed at improving the accuracy of volume estimation with the iPhone, given its advantages in terms of low cost, reduced processing time, and ease of use. By exploring methodological adjustments or combining it with other technologies, it could be possible to maximize the potential of this technology to provide more accurate volume estimates while maintaining its operational benefits.

We agreed and added to the manuscript.

Thank you for the positive evaluation of our manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The article “Assessment of New Techniques for Measuring Volume in Large Wood Chip Piles” is an interesting study on estimation the chip pile volumes by several methods. These integrate modern technique such as laser ground scanning, UAV technology, and laser ground measurement. The authors analyzed the accuracy, speed, and economic efficiency of each method. The article is very well written and scientifically documented. I could only detect a few small errors that can be fixed quickly. Below you will find my comments. I think that the figures are too many in the manuscript.

Line 130: The sources should be written [33-34], not [33, 34]. However, I don’t think that here is the right place to cite (not after the number of height which is particular in this case).

Lines 206 and 215: A dot should be deleted after the word “positions”.

Line 324: I think that a space should be added after 100 and 1000, a space before de unit.

Lines 361-362: What E, F, G, and H represent in the Figure 13? You should add an explanation as it is for A, B, C, and D.

Line 372: Add a dot after the title of Figure 14.

Line 445: Please, check the space before “Similarly”.

Lines 404, 409: The sources are written [38,39], [40,41] which is different than in introduction where on lines 32, 44 ar indicated such as [1-2], [7-8]. You should keep one way and correct this in the text.

Author Response

The article “Assessment of New Techniques for Measuring Volume in Large Wood Chip Piles” is an interesting study on estimation the chip pile volumes by several methods. These integrate modern technique such as laser ground scanning, UAV technology, and laser ground measurement. The authors analyzed the accuracy, speed, and economic efficiency of each method. The article is very well written and scientifically documented. I could only detect a few small errors that can be fixed quickly. Below you will find my comments. I think that the figures are too many in the manuscript.

Line 130: The sources should be written [33-34], not [33, 34]. However, I don’t think that here is the right place to cite (not after the number of height which is particular in this case).

Changed

Lines 206 and 215: A dot should be deleted after the word “positions”.

Corrected

Line 324: I think that a space should be added after 100 and 1000, a space before the unit.

Corrected

Lines 361-362: What E, F, G, and H represent in Figure 13? You should add an explanation as it is for A, B, C, and D.

Added

Line 372: Add a dot after the title of Figure 14.

Corrected

Line 445: Please, check the space before “Similarly”.

Corrected

Lines 404, 409: The sources are written [38,39], [40,41] which is different than in introduction where on lines 32, 44 ar indicated such as [1-2], [7-8]. You should keep one way and correct this in the text.

Corrected

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Introduction describes several application of the tested technology in several areas but excludes most of the developments using same or similar methods in the area of this paper: wood measurement. You indicated the first publication but omit the recent works. The introduction must be supplemented with this information to provide context for the paper. This information must be included.

For example:

- Purfürst T, De Miguel-Díez F, Berendt F, Engler B, Cremer T. 2023. Comparison of wood stack volume determination between manual, photo-optical, iPad-LiDAR and handheld-LiDAR based measurement methods. iForest - Biogeosciences and Forestry, Volume 16, Issue 4, Pages 243-252. https://doi.org/10.3832/ifor4153-016.

- MUND, J.-M., KATZ, N., KRAUSE, S. und CREMER, T. (2017): Hackschnitzelhaufenvermessung mittels Drohnentechnik. AFZ-DerWald 26/2017, S. 36-39

 

In addition, there are currently photo-optical or photogrammetry based solutions in the market developed for the same purpose, e.g., Pix4D Mapper which provides automatically with the volumes estimation. This should also be considered in the introduction and discussion.

Material and methods

The reference value or ground truth as well as the method to evaluate the accuracy of the methods must be indicated. You should also justify why you only tested the methods based on only one pile. There are a wide spectrum of publications which took several piles as a basis to evaluate the methods.

You described the method without any reference. If you have not developed them, such methods must be endorsed by references, citing them. Some of the methods descriptions present similarities with previously conducted research works as well as algorithms which are currently available in the market. Please indicate the corresponding references.

When describing the methods you are indicating some times how long the entire measurement process took or how long the data collection process took. I would recommend coherence at this point, either you indicate the period for the entire measurement process (include time required for data collection, data processing and volume estimation) or for the data collection in the field. Moreover, I think it would be helpful to indicate how long the corresponding subprocesses took, e.g., data collection period in the field, data processing period at office, and so on. In doing so, you could supplement your results in terms of work efficiency in the field/at office.

Results

In the section 3 you are still describing a part of the methods: the successive steps to estimate the volume from the collected data, please move that information to the section materials and methods and describe only in the section 3 the results of this study. You wrote in the introduction that your aim is to compare the methods, not show their development.

Please indicate how you calculated the final price for each method.

In table 2, describe what you meant with measuring time, data collection or data collection+data processing+volume estimation?

You are describing the accuracy of each method as well as efficiency in terms of high, low, etc. As you accurately obtained the results, please indicate the resulting figures for each parameter or define what you are meaning with such terms, e.g., "high accuracy", etc. Please indicate the reference value which you used to state that the highest accuracy was achieved by TLS Riegl Vz 600i. Please define how you evaluated the accuracy (you indicate in figure 14 precision which is not the same as accuracy. If you are meaning precision, please describe how you evaluated the precision of each method) and the difficulty or complexity. Please use the same terms in order to avoid missunderstandings, e.g.,  either difficutly or complexity.

In this section you began to discuss the results, please, move those last sentences to the discussion section.

Discussion

In the discussion a comparison of the tested methods with other developed in previoulsy conducted research works should be addressed, including solutions which are currently available in the market. In other words, recent developments must also be considered in the discussion since, the initial part of the discussion omitted developments and research studies on developing, testing, and/or using the tested methods. 

Lines 412-414 - please add the references given before since that statement is not correct.

Line 423-439 please focus on references which are similar to your topic as those given before in this review related to wood measurement, for instance, do not consider those related to mineral stockpiles.

 

 

 

 

Author Response

Introduction describes several application of the tested technology in several areas but excludes most of the developments using same or similar methods in the area of this paper: wood measurement. You indicated the first publication but omit the recent works. The introduction must be supplemented with this information to provide context for the paper. This information must be included.

For example:

- Purfürst T, De Miguel-Díez F, Berendt F, Engler B, Cremer T. 2023. Comparison of wood stack volume determination between manual, photo-optical, iPad-LiDAR and handheld-LiDAR based measurement methods. iForest - Biogeosciences and Forestry, Volume 16, Issue 4, Pages 243-252. https://doi.org/10.3832/ifor4153-016.

- MUND, J.-M., KATZ, N., KRAUSE, S. und CREMER, T. (2017): Hackschnitzelhaufenvermessung mittels Drohnentechnik. AFZ-DerWald 26/2017, S. 36-39

In our work, we considered that the development of certain individual methods, along with their detailed descriptions, limits, possibilities, and constraints, had already been covered in many published works. Therefore, we initially focused on their characteristics and the descriptions of possible applications. Nonetheless, we appreciate the additional suggestions we have incorporated.

In addition, there are currently photo-optical or photogrammetry based solutions in the market developed for the same purpose, e.g., Pix4D Mapper which provides automatically with the volumes estimation. This should also be considered in the introduction and discussion.

Were added

Material and methods

The reference value or ground truth as well as the method to evaluate the accuracy of the methods must be indicated. You should also justify why you only tested the methods based on only one pile. There are a wide spectrum of publications which took several piles as a basis to evaluate the methods.

The reference volume has been supplemented based on the company's woodchips pile volume data evidence.

You described the method without any reference. If you have not developed them, such methods must be endorsed by references, citing them. Some of the methods descriptions present similarities with previously conducted research works as well as algorithms which are currently available in the market. Please indicate the corresponding references.

The references have been added. Part of the methodological procedures used to sense and calculate the pile volume is based on the authors' work and was developed during field analysis.

When describing the methods you are indicating some times how long the entire measurement process took or how long the data collection process took. I would recommend coherence at this point, either you indicate the period for the entire measurement process (include time required for data collection, data processing and volume estimation) or for the data collection in the field. Moreover, I think it would be helpful to indicate how long the corresponding subprocesses took, e.g., data collection period in the field, data processing period at office, and so on. In doing so, you could supplement your results in terms of work efficiency in the field/at office.

The most important factor is the data collection time, as this requires actual physical effort. Processing on a computer can be done without human presence. Including post-processing time could distort the results from this perspective.

Results

In the section 3 you are still describing a part of the methods: the successive steps to estimate the volume from the collected data, please move that information to the section materials and methods and describe only in the section 3 the results of this study. You wrote in the introduction that your aim is to compare the methods, not show their development.

For better clarity, we will not move the section, as we believe it is easier to understand this way.

Please indicate how you calculated the final price for each method.

Added

In table 2, describe what you meant with measuring time, data collection or data collection+data processing+volume estimation?

Added

You are describing the accuracy of each method as well as efficiency in terms of high, low, etc. As you accurately obtained the results, please indicate the resulting figures for each parameter or define what you are meaning with such terms, e.g., "high accuracy", etc. Please indicate the reference value which you used to state that the highest accuracy was achieved by TLS Riegl Vz 600i. Please define how you evaluated the accuracy (you indicate in figure 14 precision which is not the same as accuracy. If you are meaning precision, please describe how you evaluated the precision of each method) and the difficulty or complexity. Please use the same terms in order to avoid missunderstandings, e.g.,  either difficutly or complexity.

A reference value was added, and the difference between the real and estimated values was calculated.

In this section you began to discuss the results, please, move those last sentences to the discussion section.

Discussion

In the discussion a comparison of the tested methods with other developed in previoulsy conducted research works should be addressed, including solutions which are currently available in the market. In other words, recent developments must also be considered in the discussion since, the initial part of the discussion omitted developments and research studies on developing, testing, and/or using the tested methods. 

Added

Lines 412-414 - please add the references given before since that statement is not correct.

Unfortunately, this is also the case for the operation in which the survey was conducted, as well as in other heating plants in the region, where they only have an approximate estimate of the current pile volume. We do not have a specific reference for this, as it is based on the statements of the heating plant’s operating staff.

Line 423-439 please focus on references which are similar to your topic as those given before in this review related to wood measurement, for instance, do not consider those related to mineral stockpiles.

We have included the recommended references, although we believe that pile volume measurements using these techniques are applicable to any type of piled material, not just wood. Comparative studies focusing solely on wood chips are not as numerous as they may appear.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The paper can be accepted in present form. Congratulations