CN116858130B - Three-dimensional ice shape measurement method based on pi/2 complementary double pulse width modulation mode - Google Patents
Three-dimensional ice shape measurement method based on pi/2 complementary double pulse width modulation mode Download PDFInfo
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Abstract
The invention relates to the technical field of ice shape measurement, in particular to a three-dimensional ice shape measurement method based on pi/2 complementary double pulse width modulation mode. The method comprises projecting coded structured light andcomplementary double pulse width modulation modeThe generated active structure light is transmitted to the ice surface, and then a binocular camera is adopted to collect images of the ice surface coding structure light and the active structure light; then, carrying out phase expansion and homonymy point matching on the acquired image; and finally, carrying out three-dimensional reconstruction on the ice surface to realize three-dimensional measurement of the ice surface. Innovatively by the methodThe complementary double pulse width modulation mode projects the active structure light to the ice surface, and the adopted methodThe complementary double pulse width modulation mode has good binary characteristic and extremely strong discrimination capability. The three-dimensional measurement method for the ice surface provided by the invention can be suitable for three-dimensional measurement of the ice surface with very complex reflection characteristics.
Description
Technical Field
The invention relates to the technical field of ice shape measurement, in particular to a three-dimensional ice shape measurement method based on pi/2 complementary double pulse width modulation mode.
Background
It has been found that icing during flight is one of the main contributors to aircraft flight safety. The icing of different parts of the aircraft can cause different degrees of influence, such as the icing of wings and tails can cause the change of turbulent flow fields, thereby seriously affecting the aerodynamic performance, operability and stability of the aircraft; icing of the engine inlet may cause the engine to stop and jeopardize flight safety. Therefore, the method has important significance in exploring the icing mechanism, evaluating the aerodynamic performance and safety of the aircraft under icing meteorological conditions, performing research works such as ice prevention and removal, and the like. In order to explore the icing mechanism, evaluate the aerodynamic performance of the aircraft under icing meteorological conditions and the like, researchers need to measure and study the icing appearance of the flight part under different meteorological environments. There are 3 main ways to obtain icing profile: software simulation calculation, flight test and ground simulation test. The ground simulation test is a main means for acquiring the icing appearance due to low cost and capability of obtaining quantitative results. The ground simulation test is typically performed in an icing wind tunnel.
In order to observe icing 3D contour information of a wind tunnel aircraft model in real time, researchers at home and abroad propose a method for combining face structure light with binocular vision. However, the difficulty of three-dimensional measurement by the method is quite large, and is mainly reflected in:
(1) The ice surface has the characteristic of partial smoothness, and matching of homonymous points is difficult to realize under the condition of no participation of active structured light;
(2) Under the condition of using active structured light, the ice has a high light reflection area, so that the surface reflection characteristic is very complex, and great difficulty is brought to phase analysis. The prior art generally needs to spray dark paint on the icing surface to obtain a high-contrast coded pattern image, but the application range of the measuring method is greatly limited, and the measuring method cannot be used for online measurement.
Different active structure lights correspond to different pulse width modulation modes, and different active structure lights can be emitted through DLP projection of the different pulse width modulation modes. When three-dimensional measurement is carried out on the surface of ice, a pulse width modulation mode which can adapt to a complex surface is needed, and the light energy of an active structure projected by the pulse width modulation mode overcomes the complex reflection characteristic of the ice surface, so that accurate phase analysis is realized. However, the related research of the active structure light modulation mode in the prior art is very little.
Disclosure of Invention
The method aims to solve the technical problems of high phase resolution difficulty and low measurement accuracy caused by complex reflection characteristics of the ice surface in the icing wind tunnel icing shape measurement process in the prior art. The invention provides a three-dimensional ice shape measuring method based on pi/2 complementary double pulse width modulation mode. The method comprises the following steps:
the application provides a three-dimensional ice shape measuring method based on pi/2 complementary double pulse width modulation mode, which comprises the following steps:
s10, projecting coded structured light andcomplementary double pulse width modulation mode->The generated active structure light reaches the ice surface; said->Complementary double pulse width modulation mode->The expression of (2) is:whereinxRepresenting coordinates; />And->Representing the fourier order; />Is the frequency of the reference positive signal; />Is the frequency of the carrier wave; />Is the circumference ratio; />For the first class of Bessel functions, the following is defined: />，/>As an argument of the first type of bessel function,norder of Bessel function of the first class, < ->As an exponential function +.>Is an angle variable, wherein->Representing complex symbols; />Representing complex symbols->Is->A first class of Bessel functions of the order;
s20, acquiring images of ice encoding structural light and active structural light by using a binocular camera;
s30, performing phase expansion and homonymy point matching on the acquired image;
and S40, carrying out three-dimensional reconstruction on the ice surface to realize three-dimensional measurement of the ice surface.
Further, in step S10Complementary double pulse width modulation mode->The method comprises the following steps of:
s100, setting the phase of the triangular carrier to 0, setting the phase of the reference sine signal to 0 to generateMode (S)>The mathematical expression of the pattern is:
；
wherein,mandnrepresenting the order of the fourier transform,and->，/>Is a triangular carrier phase>Bessel function of the first class, order 0,>is thatnA first class of Bessel functions of the order;
setting the phase of the triangular carrier to 0, and setting the phase of the reference sinusoidal signal toGenerate->Mode (S)>The mathematical expression of the pattern is:
；
setting the phase of the triangular carrier toPhase setting of reference sinusoidal signal to 0 generatesMode (S)>The mathematical expression of the pattern is:
；
setting the phase of the triangular carrier toThe phase of the reference sinusoidal signal is set to +.>Generate->Mode (S)>The mathematical expression of the pattern is:
；
s200, the step S100 generatesMode and->Mode subtraction to obtain +.>Mode (S)>The mathematical expression of the pattern is:
；
wherein,；
generated in step S100Mode and->Mode subtraction to obtain carrier phase of +.>Time->Mode (S)>The mathematical expression of the pattern is:
；
s300, the step S200 is performedModeAnd->Mode addition to get +.>Complementary double pulse width modulation mode->，/>Complementary double pulse width modulation mode->The mathematical expression of (2) is:
。
further, step S10 projects the coded structured light as 7 pairs of gray code structured light.
Further, step S30 uses a three-step phase shift method to realize phase unwrapping.
Further, step S30 realizes accurate matching of the same name point sub-pixels of the binocular camera by a difference method.
The beneficial effects of the invention are as follows:
1. innovatively by the methodThe complementary double pulse width modulation mode projects the active structure light to the ice surface, and the adopted methodThe complementary double pulse width modulation mode has good binary characteristic and extremely strong discrimination capability. In the conventional ice shape three-dimensional measurement method, 256 modes are needed to be distinguished when a certain point on the ice surface is measured, and the method adopts +.>Only two kinds of 0 and 255 are needed after the complementary double pulse width modulation mode projects the active structure lightThe mode is judged, so that the three-dimensional ice surface measurement method provided by the application can be suitable for three-dimensional measurement of ice surfaces with quite complex reflection characteristics.
2. The method adoptsThe complementary double pulse width modulation mode has the capability of restraining harmonic waves and eliminating higher harmonic waves, and can obtain high-quality phases under the condition that a projector is approximately focused or has small defocus amount, so that the difficulty of phase analysis is reduced. Meanwhile, even when the projector is approximately focused or has small defocus, the projected fringes have good binary characteristics, are less sensitive to the reflection characteristics of the object surface, and can improve the measurement accuracy of the surface with complex reflection characteristics.
3. Optically, when measuring a high contrast 3D surface, the mode captured by the camera is easily over-exposed due to the high reflectivity coefficient of the ice surface, resulting in a large error in the phase obtained by using the conventional phase shift algorithm. The method adoptsThe complementary double pulse width modulation mode can use an inverted stripe mode to compensate a standard mode, so that phase errors caused by overexposure of the stripe mode are eliminated or reduced, and the local overexposure adaptive capacity is realized. Under the condition that the complementary stripe patterns are not exposed simultaneously, the method can obtain accurate phases, and can realize accurate measurement of the object surface with high dynamic range.
4. Used in the methodThe complementary double pulse width modulation mode is generated by the following steps: the phase of the triangular carrier is set to 0, and the phases of the reference sinusoidal signals are set to 0 and 0 respectivelyπGenerate->Mode and->A mode; then levelMove->The triangular carrier signal sets the phase of the triangular carrier to +.>The phases of the reference sinusoidal signals are also set to 0 and 0, respectivelyπGenerate->Mode and->A mode. Then will generate +.>Mode and->Mode subtraction to obtain +.>A mode; to be generatedMode and->Mode subtraction to obtain carrier phase of +.>When (1)A mode. Finally, add->Mode and->Mode addition to get +.>Complementary double pulse width modulation mode->. Translation of the innovation of the method>Triangular carrier signal generationAnd->Finally, the +.A. is obtained by subtracting and then adding>Complementary double pulse width modulation modeThe method provides->The generation step of the complementary double pulse width modulation pattern is novel and the resulting +.>The complementary double pulse width modulation mode is also novel.
Drawings
FIG. 1 is a schematic flow chart of a three-dimensional ice shape measurement method based on pi/2 complementary double pulse width modulation mode;
FIG. 2 is a schematic illustration of the method employed in the present applicationA flow diagram of a complementary double pulse width modulation mode generation step;
FIG. 3 is a graph of the triangular carrier phase at 0, the reference sinusoidal signal phase divided into 0 to generateWaveform diagram of mode;
FIG. 4 is a triangular carrier phase of 0, the reference sinusoidal signal phase divided intoπGeneratingWaveform diagram of mode;
FIG. 5 is a triangular carrier phaseReference sinusoidal signal phase 0 generates +.>Waveform diagram of mode;
FIG. 6 is a triangular carrier phaseThe reference sinusoidal signal phase isπModulation-generated->Waveform diagram of mode;
FIG. 7 (a) showsWaveform diagram of mode;
FIG. 7 (b) isA spectrogram of the pattern;
FIG. 7 (c) isA spectrogram of the pattern;
FIG. 7 (d) isA spectrogram of the pattern;
FIG. 8 (a) showsWaveform diagram of mode;
FIG. 8 (b) isA spectrogram of the pattern;
FIG. 8 (c) isA spectrogram of the pattern;
FIG. 8 (d) isA spectrogram of the pattern;
FIG. 9 (a) shows a waveform diagram of a pi/2 complementary double pulse width modulation mode cdpwm (x);
FIG. 9 (b) is a spectrum diagram of a pi/2 complementary double pulse width modulation mode cdpwm (x);
figure 10 (a) shows a period t=60,and->Filtering the binary signal by a Gaussian filter with the size of 17 and the variance of 17/3 to generate a waveform diagram of a sine signal;
figure 10 (b) shows a period t=60,and (2) the%>Filtering the binary signal by a Gaussian filter with the size of 17 and the variance of 17/3 to generate a waveform diagram of a sine signal;
fig. 11 (a) shows a waveform diagram of a sinusoidal signal in the case where the k=1 stripe pattern is not over-exposed;
fig. 11 (b) shows a waveform diagram of a sinusoidal signal in the case of k=1.3 stripe pattern overexposure;
fig. 11 (c) shows a waveform diagram of a sinusoidal signal in the case of k=2 stripe pattern overexposure;
fig. 11 (d) shows a waveform diagram of a sinusoidal signal for the case of k=2.5 stripe pattern simultaneous exposure;
FIG. 11 (e) is a graph of the error of FIG. 11 (a) with respect to the ideal phase;
FIG. 11 (f) is an error plot of FIG. 11 (b) with its ideal phase;
FIG. 11 (g) is an error plot of FIG. 11 (c) with its ideal phase;
FIG. 11 (h) is an error plot of FIG. 11 (d) with its ideal phase;
FIG. 12 is a schematic diagram of a three-dimensional reconstruction;
FIG. 13 is a three-dimensional point cloud data graph obtained by using a conventional dpwm method for a first group of images according to an embodiment;
FIG. 14 is a three-dimensional point cloud data map obtained by the method according to the embodiment;
FIG. 15 is a cross-sectional data plot of the same 3D results of FIGS. 13 and 14;
FIG. 16 is a z-y three-dimensional point cloud data plot of a second set of images according to an embodiment of the present method;
FIG. 17 is an x-y three-dimensional point cloud data plot of an embodiment using the present method for a second set of images;
FIG. 18 is a schematic view of the first circular cross-section fit taken from FIG. 16;
FIG. 19 is a schematic view of the second circular cross-section fit taken from FIG. 16;
FIG. 20 is a schematic view of the third circular cross-section fit taken from FIG. 16;
FIG. 21 is a schematic view of the fourth circular cross-section fit taken from FIG. 16;
FIG. 22 is a schematic view of the fifth circular cross-section fit taken from FIG. 16;
fig. 23 is a schematic view of the sixth circular cross-section fit taken from fig. 16.
Detailed Description
The following description of the specific embodiments of the present invention will be given with reference to the accompanying drawings, so as to further understand the concept of the present invention, the technical problems to be solved, the technical features constituting the technical solutions, and the technical effects to be brought about. However, the description of these embodiments is illustrative, and does not constitute a specific limitation on the present invention.
The three-dimensional measurement of ice shape in icing wind tunnel test is important to research the principle of icing of aircraft wing surface and relevant research analysis.
When the ice shape is measured in three dimensions, the projector is required to project active structured light so as to facilitate post-processing and realize homonymous point matching. However, after the active structure light is used in the prior art, the reflection characteristic of the ice surface is very complex due to the semitransparent and high reflection characteristics of the ice, and the phase analysis is greatly difficult by projecting the active structure light.
The innovation of the application is based onMethod for three-dimensional measurement of ice surface by complementary double pulse width modulation mode, wherein the method adopts +.>The complementary double pulse width modulation mode is used for projecting and obtaining active structure light, and the active structure light can solve the technical problem of high phase analysis difficulty, and is described in detail as follows:
as shown in fig. 1, the method comprises the following steps: first, S10, projection-encoded structured light andcomplementary double pulse width modulation mode->The generated active structure light reaches the ice surface; said->Complementary double pulse width modulation mode->The expression of (2) is: />WhereinxRepresenting coordinates>And->Representing the Fourier order, +.>For referencing the frequency of the positive signal +.>Is the frequency of the carrier wave, ">Is of circumference rate>For the first class of Bessel functions, the following is defined: />，/>The argument of the Bessel function of the first type, which can be real or complex, if +.>If the real number is a real number, the Bessel function of the first type is a real number;nthe order of the Bessel function of the first type, which in this application is an integer, +.>As an exponential function +.>Is an angle variable, wherein->Representing complex symbols; />Representing complex symbols->Is->A first class of Bessel functions of the order;
then, S20, images of the ice encoding structured light and the passive structured light are collected using a binocular camera.
Next, S30, phase expansion and homonymy point matching are performed on the acquired image. Specifically, the phase period calculation is carried out on the acquired coded image, then the phase expansion is realized through the phase period to obtain the absolute phase, and then the homonymous point matching is carried out on the left camera and the right camera.
And finally, S40, carrying out three-dimensional reconstruction on the ice surface to realize three-dimensional measurement of the ice surface.
As shown in fig. 2, the method is employed in step S10Complementary double pulse width modulation mode->The method comprises the following steps:
first, S100, generateMode, & gt>Mode, & gt>Mode and modeMode four modes, specifically:
setting the phase of the triangular carrier to 0 and setting the phase of the reference sinusoidal signal to 0 generatesThe mode of operation is that,the pattern is shown in FIG. 3->The spectrum of the pattern is shown in fig. 7 (b); setting the phase of the triangular carrier to 0 and the phase of the reference sinusoidal signal to +.>Generate->Mode (S)>The pattern is shown in FIG. 4->The spectrum of the pattern is shown in fig. 7 (c).
The mathematical expression of the pattern is:
(1)
the mathematical expression of the pattern is:
(2)
wherein,mandnrepresenting the order of the fourier transform,and->，/>Is a triangular carrier phase>Bessel function of the first class, order 0,>is thatnBessel function of first class of orderA number.
Setting the phase of the triangular carrier toPhase setting of reference sinusoidal signal to 0 generatesMode (S)>The pattern is shown in FIG. 5->The spectrum of the pattern is shown in fig. 8 (b); setting the phase of the triangular carrier to +.>The phase of the reference sinusoidal signal is set to +.>Generate->Mode (S)>The pattern is shown in FIG. 6->The spectrum of the pattern is shown in fig. 8 (c).
The mathematical expression of the pattern is:
(3)
the mathematical expression of the pattern is:
(4)
next, S200, four patterns generated according to step S100、/>、And->Obtain->Mode and->The mode is specifically as follows:
generated in step S100Mode and->Mode subtraction to obtain +.>Mode, +.>The waveform of the pattern is shown in FIG. 7 (a), the spectrum is shown in FIG. 7 (d), and +.>The mathematical expression of the pattern is:
(5)
wherein,。
generated in step S100Mode and->Mode subtraction to obtain carrier phase of +.>Time->Mode, carrier phase is->Time->The waveform diagram of the pattern is shown in fig. 8 (a), the spectrum diagram is shown in fig. 8 (d),
the mathematical expression of the pattern is:
(6)
finally, S300, obtained according to step S200Mode and->Pattern generation method using +.>Complementary double pulse width modulation mode->. The method specifically comprises the following steps: will step by stepObtained in step S200Mode and->Mode addition to get +.>Complementary double pulse width modulation mode->，Complementary double pulse width modulation mode->The waveform of (a) is shown in FIG. 9 (a), and the spectrum is shown in FIG. 9 (b),/->Complementary double pulse width modulation mode->The mathematical expression of (2) is:
(7)
please refer toComplementary double pulse width modulation mode->The mathematical expression (7) of (2) is equal to +.>Generated->Mode and->Generated->Mode comparison, i.e. formula (5) and (6)>The number ratio of the values->The number of values is doubled, therefore +.>Complementary double pulse width modulation mode->With independently generated->The mode further suppresses the effects of harmonics. And->Complementary double pulse width modulation mode->Contains only the desired fundamental frequency and frequency inIs used in the method>Complementary double pulse width modulation mode->The fundamental frequency is increased to the original->Mode, & gt>Mode, & gt>Mode and->The method has strong capability of eliminating higher harmonics, and can obtain high-quality phase under the condition that the projector is approximately focused or has small defocus. Meanwhile, when the projector is approximately focused or has small defocus, the projected fringes have good binary characteristics and are less sensitive to the reflection characteristics of the object surface, and the measurement accuracy of the complex surface with the reflection characteristics can be improved.
Optically, when measuring a high contrast 3D surface, the mode captured by the camera is easy to be over-exposed due to the high reflectivity coefficient of the ice surface, so that the phase obtained by the traditional phase shift algorithm has a large error. The method is adoptedComplementary double pulse width modulation mode->Also has the ability to accommodate local overexposure, which can be used to achieve high dynamic range measurements, as described in detail below:
calculation ofAnd->Is an inverted stripe pattern of (a), generating a complementary stripe pattern as follows:
(8)
(9)
fig. 10 (a) and 10 (b) show a period t=60、/>、/>Andthe binary signal is filtered by a Gaussian filter with the size of 17 and the variance of 17/3 to generate a sine signal. It can be seen that when the signal amplitude is over-exposed above the dashed line, there are only two modes over-exposed at the same time, so the other two non-exposed modes can be used to calculate the phase to reduce the over-exposure error.
According to the formula (8) and the formula (9)Complementary double pulse width modulation mode->The mathematical expression of (c) is rewritable as follows:
（10）
assume whenAnd->When overexposure occurs, i.e.)>The method comprises the following steps:
（11）
it can be seen that equation (11) and equation (6) differ only by a constant, and therefore inComplementary double pulse width modulation modeDuring overexposure, the person is added with->Complementary double pulse width modulation mode->Equivalent to->Techniques. The same is true when the other two modes are over-exposed.
As shown in fig. 11 (a), 11 (b), 11 (c), 11 (d), 11 (e), 11 (f), 11 (g) and 11 (h), respectively, it is shown that when the object surface reflectance coefficients k are 1, 1.3, 2 and 2.5,complementary double pulse width modulation modeOverexposure conditions and phase errors thereof. Wherein FIG. 11 (a) shows the object surface reflectance coefficient +.>In the case of a stripe pattern which is not overexposed, the method is used +.>Complementary double pulse width modulation mode->The phase is calculated and its error from the ideal phase is calculated as in fig. 11 (e), the root mean square error of the phase being 0.0139 rad. FIGS. 11 (b) and 11 (c) show the object surface reflectivity, respectivelyCoefficient->And->In the case of overexposure, it can be clearly seen that the fringe pattern appears to be overexposed. Since there is no simultaneous overexposure between the two complementary patterns, at the point of overexposureComplementary double pulse width modulation mode->Equivalent to->Techniques.
Fig. 11 (f) shows the phase error of fig. 11 (b), fig. 11 (g) shows the phase error of fig. 11 (c), the phase root mean square error of fig. 11 (f) is 0.0161 rad, and the phase root mean square error of fig. 11 (g) is 0.0203 rad, with only a small increase compared to the non-overexposed case. FIG. 11 (d) shows the object surface reflectance coefficientIn the case of exposure, it can be clearly seen that within the dashed box, two complementary modes appear to be simultaneously exposed. Fig. 11 (h) shows the phase error of fig. 11 (d), and it can be seen that the phase error increases significantly, and the root mean square error of the phase reaches 0.0564 rad. It can be seen that the method is used with +.>Complementary double pulse width modulation mode->Accurate phase can be obtained and accurate measurement of the object surface with high dynamic range can be realized.
In the embodiment of the present application, step S10 employsDLP projectionComplementary double pulse width modulation mode->Then, a binocular camera is used to capture images on the ice surface. />
Left and right camera acquisitionComplementary double pulse width modulation mode->After the image, 7 pairs of Gray code structured lights are projected, and the embodiment of the application realizes +.>Complementary double pulse width modulation mode->And the phase expansion of the left camera and the right camera is further realized, and finally, the three-dimensional measurement of the ice-shaped surface is obtained through a three-dimensional imaging principle.
In the embodiment of the present application, the phase unwrapping adopts a three-step phase shift method, and the three-step phase shift function is expressed as:
(12)
(13)
(14)
wherein the method comprises the steps ofFor the average intensity of the fringe image, +.>Is intensity modulated. Phase->Can be calculated from the formulas (12) to (13) as follows:
(15)
the arctangent function will be obtainedWithin the range have->Discontinuous parcel phase diagram for removing +.>Discontinuity and absolute phase are obtained, and a time phase unwrapping algorithm is generally used, and the phase unwrapping is achieved by adopting a Gray code method. Absolute phase->Expressed as:
（16）
after the absolute phases of the left camera and the right camera are obtained, the homonymous point matching of the left camera and the right camera can be realized under the limit constraint of the left image and the right image, and the homonymous point sub-pixel accurate matching of the binocular camera is realized through a difference method.
As shown in fig. 12, each point in the pixel coordinate system corresponds to a line in the real coordinate system, and thus all points of the line located in the real coordinate system can be projected onto the image, that is, the pixel coordinate system. If a pair of corresponding points can be found on two or more pixel coordinate systems, they are the real coordinate system midpointsProjection on a two-pixel coordinate system.
Points of a real coordinate systemThrough the camera focus->、/>Corresponding point projected onto the pixel coordinate system +.>、/>. For the known->、/>And->、/>Two projection lines can be determined and the relevant intersection point +.>The basic linear algebra of the position.
Assume a point in a real coordinate systemExist and the coordinates in the left and right camera coordinate systems are respectivelyAnd->，/>For the focal length of the camera +.>For the baseline length, there are: /> （16）
Solving the equation, the coordinates of each point on the ice surface can be obtained,
（17）
wherein the method comprises the steps ofIs parallax, its value is +.>。
In order to verify the effectiveness of the method, a comparison experiment is carried out, wherein the comparison experiment adopts ice cubes with larger change of the reflectivity of the ice cube surface, complex reflection characteristics, exposed pixels and lower gray values. As shown in fig. 13, a three-dimensional point cloud data graph obtained by using a conventional dpwm method for the first group of images in the experiment is shown, and it can be seen that many voids and outliers exist. As shown in fig. 14, a three-dimensional point cloud data graph obtained by the method provided by the application of the first group of images in the experiment is shown, and fig. 14 only has few noise points, so that more accurate measurement is realized. For better contrast discrimination, data for the same cross-section of the 3D results in fig. 13 and 14 were obtained and plotted in fig. 15, with less error in reconstructing the surface by the present method as can be seen in fig. 15. Experimental results show that the method has better performance than the traditional dpwm method, and can realize the measurement of the high dynamic surface. In the experiment, a second group of images are also acquired, and the result of reconstructing the three-dimensional point cloud by adopting the method for the second group of images is shown in fig. 16 and 17. 6 sections are cut from fig. 16 to fit circles, and the fitting results are shown in fig. 18, 19, 20, 21, 22 and 23, respectively, and the error mean value is 0.2153mm and the variance mean value is 0.2818mm can be seen from fig. 18, 19, 20, 21, 22 and 23. It can be seen that the measurement result of the method is very accurate even in the case of ice cubes with a high light reflection surface and various adverse factors such as overall translucency and uneven transparency.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; while the invention has been described in detail with reference to the foregoing embodiments, it will be appreciated by those skilled in the art that variations may be made in the techniques described in the foregoing embodiments, or equivalents may be substituted for elements thereof; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (4)
1. The three-dimensional ice shape measuring method based on pi/2 complementary double pulse width modulation mode is characterized by comprising the following steps:
s10, projecting the coding structure light and the active structure light generated by pi/2 complementary double pulse width modulation mode cdpwm (x) onto ice; the pi/2 complementary double pulse width modulation mode cdpwm (x) has the expression:
wherein x represents a coordinate; m "and n' represent Fourier orders; f (f) 0 Is the frequency of the reference positive signal; f (f) c Is the frequency of the carrier wave; pi is the circumference ratio; j is a Bessel function of the first type, defined as follows:z is the argument of the Bessel function of the first type, n is the order of the Bessel function of the first type, e is an exponential function, beta is an angle variable, and j represents a complex symbol; j (J) 2n′-1 A Bessel function of the first type that is 2n' -1 order;
s20, acquiring images of ice encoding structural light and active structural light by using a binocular camera;
s30, performing phase expansion and homonymy point matching on the acquired image;
s40, carrying out three-dimensional reconstruction on the ice surface to realize three-dimensional measurement of the ice surface;
the pi/2 complementary double pulse width modulation mode cdpwm (x) in step S10 is obtained by:
s100, setting the phase of the triangular carrier to 0, setting the phase of the reference sine signal to 0 to generateThe mode of operation is that,the mathematical expression of the pattern is:
where m and n represent fourier orders, m=4m″ and n=2n' -1, θ c Is the triangular carrier phase J 0 Bessel function of the first class, J n A first class Bessel function of order n;
setting the phase of the triangular carrier to 0 and the phase of the reference sinusoidal signal to pi generatesThe mode of operation is that,the mathematical expression of the pattern is:
setting the phase of the triangular carrier to pi/2 and the phase of the reference sine signal to 0 to generateThe mode of operation is that,the mathematical expression of the pattern is:
setting the phase of the triangular carrier to pi/2, generating the reference sine signal with piThe mode of operation is that,the mathematical expression of the pattern is:
s200, the step S100 generatesMode and->Mode subtraction to obtain +.>Mode (S)>The mathematical expression of the pattern is：
Wherein m=2m';
generated in step S100Mode and->Mode subtraction to obtain +.sub.2 for pi/2 carrier phase>Mode (S)>The mathematical expression of the pattern is:
s300, the step S200 is performedMode and->The mode addition obtains a pi/2 complementary double pulse width modulation mode cdpwm (x), and the mathematical expression of the pi/2 complementary double pulse width modulation mode cdpwm (x) is as follows:
2. the three-dimensional ice shape measurement method based on pi/2 complementary double pulse width modulation mode according to claim 1, wherein the method comprises the following steps: and S10, projecting the coded structured light into 7 pairs of Gray code structured light.
3. The three-dimensional ice shape measurement method based on pi/2 complementary double pulse width modulation mode according to claim 1, wherein the method comprises the following steps: step S30 adopts a three-step phase shift method to realize phase unwrapping.
4. The three-dimensional ice shape measurement method based on pi/2 complementary double pulse width modulation mode according to claim 1, wherein the method comprises the following steps: and step S30, realizing accurate matching of the same name point sub-pixels of the binocular camera through a difference method.
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