Integration of Multi-GNSS PPP-RTK/INS/Vision with a Cascading Kalman Filter for Vehicle Navigation in Urban Areas

Round 1

Reviewer 1 Report

Dear Authors,

The topic/manuscript is highly relevant focusing on “…advantages of PPP-RTK over PPP and RTK into consideration, the integration of 85 multi-GNSS PPP-RTK and MEMS IMU is still left for further research”. A clear research gap has been identified. In the literature review, the results of Gao et al. [23] are quite useful (Line 76). Few major suggestions:

a.       Cascaded filter details can be added in a separate subsection

b.       Line 464-467 : Clarity shall be brought to “Vision helps constrain the error 467 divergence. ” 

c.       Results section can be improved for lucidity.

 

Other suggestions for improvement:

1.       Line 11/12: Reframe”/Correct the sentence- “However, it is challenging for 11 PPP-RTK to be applied in urban areas due to the limitation of Non-Line-Of-Sight (NLOS).

2.       Line 14: Reframe sentence without “we”.

3.       Abstract: Before mentioning the results, add a sentence(s) on peculiarity of T01 and T02.

4.       Line 29/67/120/125/128/…/177/301…/353/ 414/424/435/…507/513/519/…..: Preferably do not start a Paragraph or sentence with punctuation or With/But/What’s/For/In/ we/you/ From, except in a very specific case in a manuscript.

5.       Line 43-46: Reframe/Correct the sentence- ”……quad-constellations’ PPP and the …..”using simple set of sentences.

6.       Line 157: replace ”In addition..” by “Additionally…”

7.       Line 187: describe frames briefly as per requirement of manuscript & work.

8.       Section 2.5.PPP-RTK/INS/Vision integration model with a cascading filter, while reducing mathematical part in other sections for the readers.

9.       Suitable title can be given to section 2.6 (replace “overview” suitably) or the flowchart can be integral part of Section 2 on Methods directly.

10.   Table 1: Preferably use MKS system units, such as for mgal.

11.   Line 316-317: Reframe sentence “Shown…”

12.   Line 390: reframe sentence- “…Back to Figure 10,…..”. Figure can be referenced directly.

13.   Captions of figures can be improved.

14.   Conclusion can be rewritten highlighting the actual conclusions (gains) from the experiment in 2-3 paragraphs systematically on integration aspects of multi-GNSS PPP-RTK and MEMS IMU.

 

best wishes,

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

This study developed multi-GNSS PPP-RTK/INS/Vision fusion solution for vehicle navigation in urban and open-sky areas. The benefits of vision-aiding as well different positioning modes are demonstrated with field tests. Overall, the paper is very well written with decent novelty, strong application value, clear methodology, valid analysis and comprehensive results. Before proceeding to the publication stage, I encourage the authors to address the following minor comments:

 

1.     [Line 111] “… 6 degree of freedom (DOF) SLAM (simultaneous localization and mapping) …”

-        Please define SLAM earlier at line 108 when VI-SLAM is mentioned.

 

2.      [Line 117-118] “However, in most of these studies, only the position provided by GNSS or pseudo-range measurements were utilized in the fusion of GNSS, INS and vision.”

-        Did you imply GNSS carrier phase, Doppler should also be used in the fusion?

 

3.      [Line 144] “According to the suggestion in RINEX 3.02 …”

-        Please define or provide a reference of RINEX here.

 

4.      [Line 149] Equation 1.

-        For different constellations and signals, is inter-signal clock bias or inter-constellation time bias compensated?

 

5.      [Line 213-214] Equation 11.

-        How is lever arm correction vector determined?

 

6.      [Line 344] Figure 6

-        The reference station markers in figure 6 is not clearly visible. Please adjust to improve the visibility.

 

7.      [Line 341] “The positioning performance was evaluated by RMS (root mean square).”

-        Is there a ground truth system to provide positioning benchmark for error analysis?

 

8.      [Line 407] Figure 9

-        In figure 9, the authors compared the positioning accuracy performance between different positioning modes. Some readers may be interested in to know what frequency bands are used in GPS and Beidou GNSS data (common set between your rover and reference station)?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf