A Practical Interlacing-Based Coverage Path Planning Method for Fixed-Wing UAV Photogrammetry in Convex Polygon Regions

Round 1

Reviewer 1 Report

In this paper the authors investigate the coverage path planning problems  for a fix-wing UAV in convex polygon regions considering the pratical task requirements in photogrammetry.

In the introduction the authors introduce the problem of using  fix-wing UAV in a large detection area and the right way to semplify the path planning problem with a complete coverage of ROI.

For me the paper is well done 

Author Response

The co-authors and I would like to thank you for the time and effort spent in reviewing the manuscript. We are grateful for your recognition of our manuscript.

Reviewer 2 Report

The paper focuses on the optimization of the path planning for a fixed-wing UAV in convex polygon regions for photogrammetry application. The new model Interlaced back-and-forward pattern proposed is compared with the classical approach and practical tests are performed to demonstrate the results.

The paper is clearly presented and well organized.

Some remarks:.

Line 26 – 29

“When UAVs perform these applications, a basic concern is how to get a single high-resolution image that covers the entire region of interest (ROI) [6], known as photogrammetry and remote sensing (PaRS)”

This sentence is not well-written, please revise. The UAVs acquire high-resolution images that can be elaborated with PARS techniques to obtain metric products (for example DEM, ortohmosaics, ecc).

 

For a real and practical case of photogrammetry that uses SFM algorithm the overlap between adjacent images (sidelap) is higher than 20%, atleast 45 – 50%.

It is not clear how the author establishes the minimum radius of turning (Rmin).

Author Response

The co-authors and I would like to thank you for the time and effort spent in reviewing the manuscript. We have incorporated your suggestions into this revision. Please see the attachment of “Response_to_the_reviewer_2.docx”

Author Response File: Author Response.docx

Reviewer 3 Report

Section 4.1. Coordinate conversion might be different based on the scale of the ROI. For small ROI, the conversion can be simplified as a rigid body transformation. While for large-scale ROI, earth radius needs to be considered. The authors should clarify the scale of the ROI in the context.

 

 

It seems the method assumes the UAV flies at the same speed across the flight. This assumption does not hold in practice because fixed-wing UAVs normally decrease the speed while entering a curve. The performance of the method only real-world condition needs further justification.

 

 

In simulations, how the heights (150m/120m) are selected? If the focus of the study is UAV photogrammetry. The height needs to be computed by the selected camera resolution, camera angle,  and the required spatial resolution of the inspection (i.e., 1cm/pixel, 2cm/pixel, etc). However, the information is missing in the experiments. Similarly, why speeds 20m/s and 25m/s are selected? 

 

 

The study used two simulation cases (with selected parameters) to validate the presented method. The readers are more interested in when the presented method outperforms the conventional method. And under what condition, the method performs the same or even worse than the conventional one? The reviewer recommends the authors to add one or multiple plots that compare the flight performance (e.g., distance, time) of the two methods under varied parameters (i.e., 10m/s, 20m/s, …, 50m/s for flight speeds and 1mm/px, 5mm/px, …, 10cm/px for selected spatial resolution).

 

 

Table 2/3. Adding a column to show the percentage of the improvement of flight efficiency can better demonstrate the method's performance to the readers.

 

 

Why the method is only tested on a concave region? It seems the method only improves the turning paths that are only located outside of the scanning area, the method should be applicable to concave areas (by employing other CPP variants in the straight section). An experiment on a concave region is needed to increase the soundness of the evaluation.  

 

 

English editing is needed.

 

 

Author Response

The co-authors and I would like to thank you for the time and effort spent in reviewing the manuscript. We have incorporated your suggestions into this revision. Please see the attachment of “Response_to_the_reviewer_3.docx”

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

The reviewer thanks the authors' effort to revise the manuscript.

 

Just minor remarks:

The input parameters need to be summarized in a table for interested readers to reproduce the experiments. 

 

As in figures 11-12, it seems both methods assume the UAVs only collect images at the straight section (the turning areas are located outside of the ROI).  Is it possible to also enable the UAVs to collect images while making turns? And the overall flight distances can be further reduced.

Author Response

The co-authors and I would like to thank you for the time and effort spent in reviewing the manuscript. We have incorporated your suggestions into this revision. Please see the attachment of “Response_to_the_reviewer_3_(Round 2).docx”

Author Response File: Author Response.docx