A Strain-Gauge-Based Method for the Compensation of Out-of-Plane Motions in 2D Digital Image Correlation
Round 1
Reviewer 1 Report
The main contribution of this paper is the use of strain gauges to obtain some of the coefficients needed to compensate errors from non-perpendicularity of the object to the camera. The work follows the line of work already started by other researchers that are well described and referenced in the introduction. However, all the figures and equations included in section 2.1 are just a copy from those that appear at least in references 7, 8, 9 and 11. Additionally, those references do not appear in that section, only in the Introduction; therefore, it is not clear the authorship of all section 2.1.
My recommendation is to cite those paper at the beginning of section 2.1 and include only the last relevant equation for the actual work done in this paper. With this changes, although the novelty is not quite big, I think that it is enough to be published.
Author Response
Dear Reviewer,
Please see the attachment for a point-by-point response to your comments.
Kind regards,
Carl-Hein Visser
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors discuss a means of improving DIC deformation analysis by adding strain gauge data 'into the mix' and propose algorithmic means of reducing error. The research question is clearly posed, the treatment is described in detail starting with basics and taking the consideration to the point of algorithm formulation, followed by example of application.
Whilst the treatment is technically sound, some of the underlying motivation given by the authors can be questioned from the following angle:
The attractiveness of DIC deformation analysis lies in the possibility of performing non-contact direct digital measurements without significant sample preparation or sensor attachment. The authors argue that getting rid of the second camera requirement in stereo DIC reduces the setup overhead, but then propose to replace it with strain gauge(s) mounted on the sample. Clearly, this introduces additional hassle in terms of hardware and software, e.g. conversion of essentially analog signal into digital for subsequent use in the algorithm.
Furthermore, a relevant issue here concerns non-flatness of sample that changes the surface inclination to the imaging beam direction - this may be compensated for in stereo DIC (at least in one 'plane'), but is not taken into account by strain gauge correction, as far as I can see.
I suggest the authors take these considerations into account and address them in their manuscript.
Having said that, I feel that the authors have done enough to warrant presenting their work to the readers - although it is a different matter, of course, whether their approach is likely to be taken up and used.
Author Response
Dear Reviewer,
Please see the attachment for a point-by-point response to your comments.
Kind regards,
Carl-Hein Visser
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
I see the changes that the authors made, and they try to solve the problems stated in my previous review. The figures and equations now are referenced, and some intermediate algebras have been eliminated. However, I still think that the figures 1, 2 and 3 does not add anything interesting to this manuscript because they can be found in many previous papers.
On the other hand, I think that this work could be helpful to simplify the compensation method for image laboratory experiments, which nowadays are most of the image applications in civil engineering, unfortunately.
I recommend reviewing the text between lines 119 and 131, as it seems a bit odd for me after the modifications done in the equations in that section.
Author Response
Dear reviewer,
Please find my rebuttal letter, which provides a point-by-point response to your comments, attached.
Kind regards,
Carl-Hein Visser
Author Response File: Author Response.pdf
