REVIEW 4 major objections 4 minor 39 references
Simultaneous two-dimensional velocity and distance measurements based on laser triangulation
T0 review · 4 major / 4 minor · reviewed 2026-08-12 · deepseek-v4-flash
Pith's one-line read This paper claims a standard laser triangulation sensor can measure lateral velocity and axial distance in one shot, with errors and uncertainties down to one part in ten thousand.
desk verdict A plausible and well-tested new combination for laser triangulation—speckle-correlation lateral velocity and edge-based distance—but the velocity model needs a validity bound before the general claims can stand. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing machinery is the pair of similar-triangle lateral displacement formulas, Eqs. (2) and (3), together with Eq. (4) for velocity; the axial channel uses the same triangulation transfer relation, Eq. (5), applied to the spot edge rather than the spot centroid. The signal-processing partners are the ZNSSD digital image correlation that finds the speckle translation, the Canny operator that locates the spot edge, and Zernike moments that refine the edge to sub-pixel position.
What would settle it
Move a rough target at a known lateral velocity while decreasing surface roughness or increasing the displacement per frame until the speckle correlation between adjacent frames is lost; if the digital-image-correlation velocity departs from the stage velocity by more than the claimed $10^{-4}$ once the per-frame displacement exceeds the speckle correlation length, the rigid-translation assumption fails.
Extended reading notes
Core claim
The central claim is that a lateral motion of the measured surface translates the speckle pattern inside the imaging spot, and this translation is proportional to the surface displacement through two geometric-optics equations, one for the left half and one for the right half of the beam spot. Adding the two half-beam displacements and dividing by the camera acquisition period gives the lateral velocity. In the same acquisition, the paper claims, the edge of the imaging spot moves when newly illuminated surface is higher or lower than the surface it replaces, so tracking that edge with Canny detection and Zernike-moment sub-pixel positioning yields the axial distance. This local edge position method turns surface microstructure from a source of uncertainty into the quantity being measured, and increases lateral sampling resolution from the beam-spot diameter $2\omega$ to the per-frame motion length $v t$, about a factor of 44 in the reported experiment.
Load-bearing premise
The velocity channel assumes that when the surface moves sideways, the speckle pattern inside the imaging spot shifts with it as a rigid pattern, so the correlation peak is the true geometric lateral displacement.
Editorial extensions
If this is right
- Any existing laser triangulation system could add lateral velocity and axial distance measurement without optical changes, because both new channels are computed from the same camera images.
- The lateral sampling step of the distance channel becomes $v t$ instead of the beam diameter, so the same sensor can profile surface features smaller than the illumination spot while the object moves.
- Maximum measurable lateral velocity scales as $2\omega/t$, so using a faster camera extends the speed range; the paper's demonstration at 100 Hz and 1--10 mm/s is a lower bound on what the method can do.
- A vector decomposition of the lateral velocity measurement yields a route to three-dimensional shape measurement from a single triangulation sensor, with dynamic applications such as rotating workpiece shape, blade or gear motion, and particle velocity in fluids.
Reading between the lines
- The speckle-translation model implicitly assumes the speckle pattern moves rigidly with the surface over one frame; where the lateral displacement per frame exceeds the speckle correlation length, the correlation peak may track decorrelation rather than true geometric displacement, so a quantitative bound linking allowable displacement to surface roughness would define the usable envelope.
- Because the distance channel's lateral resolution equals $v t$, the same hardware offers a trade-off between velocity range and spatial resolution, and higher camera rates would soften that trade-off.
- The two channels share one detector and one beam, so the concept should extend to two-dimensional velocity fields by scanning the beam or using a line-shaped illumination profile, a direction the paper leaves open.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proposes extending laser triangulation sensors to simultaneous lateral velocity and axial distance measurement. The velocity model (Section 2.2) is based on tracking the lateral shift of the laser speckle pattern with digital image correlation, with geometric relations derived for the two halves of the beam spot. The distance method (Section 2.3) uses edge detection, rather than the whole-spot centroid, to measure axial position, and claims to increase lateral resolution from the beam diameter 2ω to the per-frame travel v·t. Experiments on a metal specimen with 6.3 μm roughness, using a precision motion stage and a confocal sensor as references, report relative errors and uncertainties generally below about 1%, with best values near 0.04%, and a simultaneous surface profile whose roughness matches the confocal reference.
Significance. If the central claims hold, a standard laser triangulation sensor could simultaneously provide lateral velocity and axial distance with micron-level accuracy, turning a single-axis industrial sensor into a two-axis dynamic metrology tool. The strengths of the paper are genuine: the measurement models in Eqs. (2)-(5) are parameter-free geometric relations based on measured angles and lengths; the only hand-selected parameter is the correlation-window radius r=20; and the validation is performed against external references (a calibrated motion stage and a confocal sensor) rather than by fitting to the target quantities. The reported best relative error of 0.04% and the simultaneous velocity/distance acquisition are meaningful experimental data. However, the generality of the velocity claim is not established by the current analysis, and some aspects of the derivation and its link to the algorithm need clarification before the manuscript can be accepted.
major comments (4)
- [Section 2.2, Eqs. (2)-(4)] The velocity model assumes that a lateral object displacement produces a corresponding lateral translation of the speckle pattern in the imaging spot. The manuscript itself, however, states in Section 2.1 that lateral motion makes the speckle pattern 'partially change'. For a fixed Gaussian illumination, the coherent image field after an object shift δ is a convolution of the fixed beam amplitude with the shifted surface reflectance, and it is an exact translation only in the limit of uniform illumination or very small δ/2ω. No criterion is given that connects the allowable per-frame displacement δ=v·t to the beam diameter, the speckle statistics set by surface roughness, or the DIC window radius. In particular, the stated maximum v_max=2ω/t implies δ=2ω, at which the illuminated patch is completely renewed and the correlation peak must vanish. The experiments use δ=10–100 μm with 2ω=442 μm, a favorable regime, but the general claim of lateral velocity measurement is unsupported beyond this regime. Please add a quantitative validity bound or an experimental mapping of the range of per-frame displacements and roughnesses over which the DIC peak equals the geometric displacement.
- [Section 2.2, Eq. (2)] The notation in the derivation of Eq. (2) is internally inconsistent. The text states OK'=L1'+M'N'·cosβ and K'M'=M'A'·sinβ, and then defines S'_1=M'A' as the speckle displacement. Since M'N' and M'A' are written as different segments, the similarity relation △OKM∼△OK'M' does not lead to Eq. (2) without additional definitions or algebra. As written, the equation is not derivable from the preceding geometric relations. Please rewrite this paragraph with a consistent set of image-side coordinates, or define clearly which segment on the CMOS corresponds to S'_1 and which segment appears in each of OK' and K'M'.
- [Sections 2.2 and 2.4] There is a gap between the theoretical model and the implemented algorithm. The model splits the object displacement into S1 (left half of the beam spot) and S2 (right half), with different signs in the denominators of Eqs. (2) and (3), and forms the total as S_L=S1+S2. The measurement procedure in Section 2.4, however, computes a single DIC displacement of a window centered on the image-spot centroid, and it does not explain how S'_1 and S'_2 are separated or which of Eqs. (2) and (3) is applied to a given per-frame shift. Because the two equations are not equivalent at finite shifts, the processing chain described is not uniquely determined by the model. Please specify the exact inversion used in the data processing, including how the left/right split is handled for a small per-frame displacement.
- [Section 3, Figs. 9 and 10] The claim that the edge-detection method increases lateral resolution from 442 μm to 10 μm is not directly validated. The experiments compare only a scalar roughness parameter with the manufacturer/confocal value; no pointwise profile comparison with the confocal sensor is shown, and no known lateral feature (step, pitch, or bar target) is used to assess spatial resolution. The sampling interval v·t is not by itself a lateral resolution: resolution concerns the ability to distinguish adjacent surface features, which depends on the optical footprint and the edge-localization response. To support the abstract's claim of an order-of-magnitude lateral-resolution improvement, please provide a direct resolution test or a pointwise comparison with the confocal reference profile.
minor comments (4)
- [Abstract and Figs. 8 and 10] The statement that 'relative error and relative uncertainty can reach 10^{-4}' is stronger than the reported numbers: the best relative errors are about 0.04% (4×10^{-4}), while the relative uncertainties in Figs. 8 and 10 are mostly below 0.09% and 0.98%, respectively. Please rephrase to state the actual best values and distinguish error from uncertainty.
- [Section 2.3, Fig. 4] The symbols p' and b' are used for the edge shifts in Fig. 4 but are not explicitly defined in the text as the corresponding image-plane displacements; please add definitions and indicate their positive directions.
- [Section 3] The pixel size of the CMOS and the size of the imaging spot in pixels are not given, so the reader cannot relate the DIC window radius r=20 px to the surface displacement in micrometers or to the speckle size. Please provide these values.
- [Section 2.4, Fig. 5] The flowchart text 'Perform sub-pixel positioning of the original speckle using Zernike moments' appears to refer to the imaging-spot edge rather than to a speckle; please make the terminology consistent with the edge-detection procedure described in the text.
Circularity Check
No significant circularity: the measurement models are geometric and validated against external references.
full rationale
The paper's central derivation chain is self-contained. The lateral velocity model (Eqs. 2-4) is a parameter-free geometric mapping from measured speckle-pattern displacement S' to object displacement S, based on similar triangles and the Scheimpflug condition; no target velocity or distance is used as an input to the model. The axial distance formula (Eq. 5) is a standard triangulation equation; although cited to the authors' prior work [36], it is an explicit algebraic relation involving only angles, lengths, and focal length, so the self-citation is not load-bearing. The beam-radius formula is textbook Gaussian optics, and the maximum-velocity bound v_max = 2ω/t is a stated sampling-limit assumption, not a fitted result. Experimental validation uses independent references (a precision motion stage and a confocal sensor), and the reported relative errors and uncertainties are measured against those external values. The only hand-chosen quantity, the correlation-window radius r=20, is a processing parameter balancing speed and noise and is not fitted to the reported accuracy. The claim that edge detection increases lateral resolution from 2ω to v·t is an analytic consequence of the sampling geometry rather than an empirical prediction, so it is not circular. The physical assumption that a lateral shift produces a corresponding speckle shift is a modeling assumption whose validity range could be questioned, but that is a correctness/robustness concern, not circularity.
Assumptions & free parameters
free parameters (1)
- Correlation window radius r =
20 pixels
assumptions (6)
- domain assumption Scheimpflug condition (Eq. 1) keeps the imaging spot in focus over the measurement range.
- domain assumption Under lateral translation of the rough surface, the speckle pattern in the imaging spot shifts bodily for small displacements.
- domain assumption The ZNSSD cross-correlation peak between adjacent speckle images equals the geometric lateral displacement of the surface.
- domain assumption Eq. (5), the standard axial triangulation formula taken from Ref. [36], is valid for sub-pixel edge displacements.
- domain assumption A height step at the entering beam edge changes the reflection angle and shifts the imaging spot edge by p' or b' as drawn in Fig. 4.
- standard math Thin-lens imaging law 1/L1 + 1/L1' = 1/f.
Cite this review
Pith. "Pith review of Simultaneous two-dimensional velocity and distance measurements based on laser triangulation." pith.science (2026). https://pith.science/paper/GVHOFWMN
@misc{pith2026241119669,
author = {Pith},
title = {Pith review of: Simultaneous two-dimensional velocity and distance measurements based on laser triangulation},
year = {2026},
howpublished = {\url{https://pith.science/paper/GVHOFWMN}},
note = {Machine review of arXiv:2411.19669}
}
read the original abstract
Laser triangulation sensors are widely used in industry for surface inspection due to simple setup, micron precision and low cost. Conventional laser triangulation methods only enable axial distance measurement limiting further applications, and their lateral resolution is limited by surface microstructure. For overcoming these issues, based on the geometric optics we propose novel theoretical models and methods to achieve lateral velocity measurement. Moreover, a novel axial distance measurement method using edge detection is presented, which can increase the lateral resolution by the order of one magnitude. The performance of the proposed methods are validated through simultaneous orthogonal velocity and distance measurements on a moving established metal specimen, showing the relative error and relative uncertainty can reach 10^{-4}. The versatility of this multi degree of freedom measurement method paves the way for its broad application across all laser triangulation systems. Therefore, this simultaneous two-dimensional velocity and distance sensing approach can propel advancements in dynamic behavior discipline, including but not limited to motion mechanology and fluid mechanics.
Figures
Figures from the paper (7 more)
Reference graph
Works this paper leans on
-
[1]
Optical, in situ, three-dimensional, absolute shape measurements in cnc metal working lathes,
R. Kuschmierz, A. Davids, S. Metschke,et al., “Optical, in situ, three-dimensional, absolute shape measurements in cnc metal working lathes,” The Int. J. Adv. Manuf. Technol.84, 2739–2749 (2016)
work page 2016
-
[2]
H. Zhang, D. Anders, M. Löser,et al., “Non-contact, bi-directional tool tip vibration measurement in cnc milling machines with a single optical sensor,” Mech. Syst. Signal Process.139, 106647 (2020)
work page 2020
-
[3]
A. Fischer, L. Büttner, J. Czarske,et al., “Measurements of velocity spectra using time-resolving doppler global velocimetry with laser frequency modulation and a detector array,” Exp. fluids47, 599–611 (2009)
work page 2009
-
[4]
H. Zhang, “Laser interference 3-d sensor with line-shaped beam based multipoint measurements using cylindrical lens,” Opt. Lasers Eng.159, 107218 (2022)
work page 2022
-
[5]
P. J. Bills, R. Racasan, R. Underwood,et al., “Volumetric wear assessment of retrieved metal-on-metal hip prostheses and the impact of measurement uncertainty,” Wear274, 212–219 (2012)
work page 2012
-
[6]
R. J. Hocken and P. H. Pereira,Coordinate measuring machines and systems (CRC Press, 2016)
work page 2016
-
[7]
Highly accurate non-contact characterization of engineering surfaces using confocal microscopy,
H.-J. Jordan, M. Wegner, and H. Tiziani, “Highly accurate non-contact characterization of engineering surfaces using confocal microscopy,” Meas. Sci. Technol.9, 1142 (1998)
work page 1998
-
[8]
Adaptive optics confocal microscopy using direct wavefront sensing,
X. Tao, B. Fernandez, O. Azucena,et al., “Adaptive optics confocal microscopy using direct wavefront sensing,” Opt. letters 36, 1062–1064 (2011)
work page 2011
Show all 39 references
-
[9]
An overview of depth cameras and range scanners based on time-of-flight technologies,
R. Horaud, M. Hansard, G. Evangelidis, and C. Ménier, “An overview of depth cameras and range scanners based on time-of-flight technologies,” Mach. vision applications27, 1005–1020 (2016)
2016
-
[10]
Laser ranging: a critical review of unusual techniques for distance measurement,
M.-C. Amann, T. M. Bosch, M. Lescure,et al., “Laser ranging: a critical review of unusual techniques for distance measurement,” Opt. engineering40, 10–20 (2001)
2001
-
[11]
Low-coherence interferometry–an advanced technique for optical metrology in industry,
M. Dufour, G. Lamouche, V. Detalle,et al., “Low-coherence interferometry–an advanced technique for optical metrology in industry,” Insight-Non-Destructive Test. Cond. Monit.47, 216–219 (2005)
2005
-
[12]
Dispersive white-light interferometry for absolute distance measurement with dielectric multilayer systems on the target,
U. Schnell, S. Gray, and R. Dändliker, “Dispersive white-light interferometry for absolute distance measurement with dielectric multilayer systems on the target,” Opt. Lett.21, 528–530 (1996)
1996
-
[13]
Fiber optic white light interferometer for areal surface measurement,
G. Zhang, S. Yang, J. Fluegge, and H. Bosse, “Fiber optic white light interferometer for areal surface measurement,” Meas. Sci. Technol.31, 025005 (2019)
2019
-
[14]
Optical coherence tomography,
D. Huang, E. A. Swanson, C. P. Lin,et al., “Optical coherence tomography,” Science254, 1178–1181 (1991)
1991
-
[15]
Measuring large step heights by variable synthetic wavelength interferometry,
S.-H. Lu and C.-C. Lee, “Measuring large step heights by variable synthetic wavelength interferometry,” Meas. Sci. Technol. 13, 1382 (2002)
2002
-
[16]
Precision measurement and nondestructive testing by means of digital phase shifting speckle pattern and speckle pattern shearing interferometry,
L. Yang, W. Steinchen, M. Schuth, and G. Kupfer, “Precision measurement and nondestructive testing by means of digital phase shifting speckle pattern and speckle pattern shearing interferometry,” Measurement16, 149–160 (1995)
1995
-
[17]
Phase-shifting digital holography,
I. Yamaguchi and T. Zhang, “Phase-shifting digital holography,” Opt. letters22, 1268–1270 (1997)
1997
-
[18]
Fast profilometer for the automatic measurement of 3-d object shapes,
S. Tang and Y. Y. Hung, “Fast profilometer for the automatic measurement of 3-d object shapes,” Appl. Opt.29, 3012–3018 (1990)
1990
-
[19]
Reconstructionofsurfacesof3-dobjectsbym-arraypatternprojectionmethod,
H.Morita,K.Yajima,andS.Sakata,“Reconstructionofsurfacesof3-dobjectsbym-arraypatternprojectionmethod,” in 1988 Second International Conference on Computer Vision, (IEEE, 1988), pp. 468–473
1988
-
[20]
Range sensing by projecting multiple slits with random cuts,
M. Maruyama and S. Abe, “Range sensing by projecting multiple slits with random cuts,” IEEE Trans. on Pattern Anal. Mach. Intell.15, 647–651 (1993)
1993
-
[21]
Determination of displacements using an improved digital correlation method,
M. Sutton, W. Wolters, W. Peters,et al., “Determination of displacements using an improved digital correlation method,” Image vision computing1, 133–139 (1983)
1983
-
[22]
Whole field sheet-metal tensile test using digital image correlation,
Y. Wang, J. Jiang, C. Wanintrudal,et al., “Whole field sheet-metal tensile test using digital image correlation,” Exp. Tech. 34, 54–59 (2010)
2010
-
[23]
Insitu3dprofilometryofroughobjectswithalateralshearinginterferometry range finder,
M.Frade,J.M.Enguita,andI.Álvarez,“Insitu3dprofilometryofroughobjectswithalateralshearinginterferometry range finder,” Opt. Lasers Eng.50, 1559–1567 (2012)
2012
-
[24]
Non-contact on-machine measurement using a chromatic confocal probe for an ultra-precision turning machine,
X. Zou, X. Zhao, G. Li,et al., “Non-contact on-machine measurement using a chromatic confocal probe for an ultra-precision turning machine,” The Int. J. Adv. Manuf. Technol.90, 2163–2172 (2017)
2017
-
[25]
Time-averaged in-line digital holographic interferometry for vibration analysis,
A. Asundi and V. R. Singh, “Time-averaged in-line digital holographic interferometry for vibration analysis,” Appl. optics 45, 2391–2395 (2006)
2006
-
[26]
Optical inline inspection detecting 3d defects on complex free-form surfaces in harsh production environments,
M. Strohmeier, M. Schröder, and C. Faber, “Optical inline inspection detecting 3d defects on complex free-form surfaces in harsh production environments,” tm-Technisches Messen86, 335–344 (2019)
2019
-
[27]
Design of optical triangulation devices,
Z. Ji and M.-C. Leu, “Design of optical triangulation devices,” Opt. & Laser Technol.21, 339–341 (1989)
1989
-
[28]
Lasertriangulation: fundamentaluncertaintyindistancemeasurement,
R.G.Dorsch,G.Häusler,andJ.M.Herrmann,“Lasertriangulation: fundamentaluncertaintyindistancemeasurement,” Appl. Opt.33, 1306–1314 (1994)
1994
-
[29]
Automatic optical structure optimization method of the laser triangulation ranging system under the scheimpflug rule,
Z. Nan, W. Tao, and H. Zhao, “Automatic optical structure optimization method of the laser triangulation ranging system under the scheimpflug rule,” Opt. Express30, 18667–18683 (2022)
2022
-
[30]
J. W. Goodman,Speckle phenomena in optics: theory and applications (Roberts and Company Publishers, 2007)
2007
-
[31]
Camera-based speckle noise reduction for 3-d absolute shape measurements,
H. Zhang, R. Kuschmierz, J. Czarske, and A. Fischer, “Camera-based speckle noise reduction for 3-d absolute shape measurements,” Opt. express24, 12130–12141 (2016)
2016
-
[32]
Miniaturized interferometric 3-d shape sensor using coherent fiber bundles,
H. Zhang, R. Kuschmierz, and J. Czarske, “Miniaturized interferometric 3-d shape sensor using coherent fiber bundles,” Opt. Lasers Eng.107, 364–369 (2018)
2018
-
[33]
Analysis of imaging for laser triangulation sensors under scheimpflug rule,
A. Miks, J. Novak, and P. Novak, “Analysis of imaging for laser triangulation sensors under scheimpflug rule,” Opt. express 21, 18225–18235 (2013)
2013
-
[34]
Svelto and D
O. Svelto and D. C. Hanna,Principles of lasers, vol. 4 (Springer, 1998)
1998
-
[35]
Experimental investigations and modeling of interference fringe geometry in line-shaped gaussian beam intersections for laser doppler sensors,
H. Zhang, J. Wang, and S. Wang, “Experimental investigations and modeling of interference fringe geometry in line-shaped gaussian beam intersections for laser doppler sensors,” Photonics10, 1132 (2023)
2023
-
[36]
Automatic optimization design of laser triangulation ranging sensors using an improved genetic algorithm,
H. Zhang, S. Wang, and J. Wang, “Automatic optimization design of laser triangulation ranging sensors using an improved genetic algorithm,” Measurement p. 115739 (2024)
2024
-
[37]
Recent progress in digital image correlation,
B. Pan, “Recent progress in digital image correlation,” Exp. mechanics51, 1223–1235 (2011)
2011
-
[38]
A computational approach to edge detection,
J. Canny, “A computational approach to edge detection,” IEEE Trans. on pattern analysis machine intelligence pp. 679–698 (1986)
1986
-
[39]
Zernike-moment-based image super resolution,
X. Gao, Q. Wang, X. Li,et al., “Zernike-moment-based image super resolution,” IEEE Trans. on Image Process.20, 2738–2747 (2011)
2011
Reviewed August 12, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.