Method for measuring the geometry of a glazing by projection of a random light pattern
A computer-implemented method for measuring the three-dimensional geometry of a mineral glass-based glazing during or just after a temperature shaping operation. The method implements digital processing and calculations, based on the principles of stereocorrelation, of digital images of a random light pattern projected onto the surface of a transparent glazing. It makes it possible in particular to determine the shape or the three-dimensional geometry of a transparent glazing, the surface of which not be totally opacified and/or which radiates under the effect of temperature.
1. A computer-implemented method for determining the three-dimensional geometry of a transparent glazing based on a mineral glass, said method using, as input data:
a digital reference model of the three-dimensional geometry of the glazing, and
at least two digital images of a random light pattern projected onto a surface of the glazing, said at least two digital images representing said pattern at two different observation angles relative to a normal to the surface of the glazing;
said method providing, as output data, a digital model of the three-dimensional geometry of said glazing;
said method comprising:
(a) a step of anchoring the digital reference model to one of the digital images by at least three anchoring points;
(b) a step of calculating, based on the digital reference model, two virtual digital images of the glazing at the same two observation angles as those of the two digital images provided as input data;
(c) a step of calculating residues corresponding to differences between the two virtual images obtained in step (b) and the at least two digital images provided as input data, and
(d) a step of iterating steps (b) and (c), each iteration comprising a step of calculating a modified digital model based on a prior modified digital model provided as input datum for said step (d), so as to minimise values of the residues until the values are under a previously defined threshold value σ, the modified digital model then corresponding to an output datum.
2. The method according to claim 1 , wherein the random light pattern is formed of light dots randomly distributed on the surface of the glazing and has a random distribution in terms of size and light density.
3. A non-transitory computer readable storage medium comprising instructions which, when the instructions are executed by a computer, cause said computer to execute the steps of the method according to claim 1 .
4. The process according to claim 1 , wherein the glazing has a temperature such that a wavelength corresponding to a maximum radiance thereof is between 2 μm and 6 μm.
5. The process according to claim 4 , wherein the glazing is based on soda-lime-silica glass and the temperature of the glazing is between 300° C. and 1000° C.
6. The process according to claim 5 , wherein the temperature of the glazing is between 400° C. and 650° C.
7. The process according to claim 1 , wherein the at least two images that are used as input data are obtained by projecting the random light pattern onto the surface of the glazing and acquiring the at least two images in a wavelength range of the electromagnetic spectrum of between 435 nm and 530 nm.
8. The process according to claim 7 , wherein the wavelength range of the electromagnetic spectrum is between 465 nm and 490 nm.
9. A process for measuring the three-dimensional geometry of a transparent glazing based on mineral glass, said process comprising the following steps:
(a) projecting a random light pattern onto a surface of the glazing;
(b) simultaneously and independently acquiring at least two digital images of said random light pattern by two digital optical devices oriented at two different acquisition angles relative to a normal of the surface of the glazing, and
(c) determining the three-dimensional geometry of the glazing using a method, implemented by computer, for determining the three-dimensional geometry of a transparent glazing based on a mineral glass,
wherein the at least two digital images acquired in step (b) and a digital reference model of the three-dimensional geometry of the glazing are provided as input data of the method for determining the three-dimensional geometry of a transparent glazing based on a mineral glass, and
wherein the method for determining the three-dimensional geometry of a transparent glazing based on a mineral glass includes
(i) a step of anchoring the digital reference model to one of the at least two digital images by at least three anchoring points;
(ii) a step of calculating, based on the digital reference model, two virtual digital images of the glazing at the same two observation angles as those of the at least two digital images provided as input data;
(iii) a step of calculating residues corresponding to differences between the two virtual images obtained in step (ii) and the at least two digital images provided as input data, and
(iv) a step of iterating steps (ii) and (iii), each iteration comprising a step of calculating a modified digital model based on a prior modified digital model provided as input datum for said step (iv), so as to minimise values of the residues until the values are under a previously defined threshold value σ, the modified digital model then corresponding to an output datum.
10. The process according to claim 9 , wherein the light pattern is formed of light dots randomly distributed on the surface of the glazing and has a random distribution in terms of size and light density.
11. The process according to claim 9 , wherein the two digital optical devices are provided with neutral-density filters, the density being between 2 and 400.
12. The process according to claim 11 , wherein the density is between 8 and 64.
13. The process according to claim 9 , further comprising, before step (a), a step of dispersing a pulverulent material, and wherein said projecting of the random light pattern in step (a) is carried out by illumination, with visible light, a pulverulent material dispersed on the surface of the glazing.
14. The process according to claim 13 , wherein the illumination is carried out in transmission.
15. The process according to claim 13 , wherein the illumination is carried out in reflection at a projection angle of between 35° and 55° relative to the normal to the surface of the glazing.
16. The process according to claim 13 , wherein the illumination is carried out in a wavelength range of the electromagnetic spectrum of between 435 nm and 530 nm.
17. The process according to claim 9 , wherein a background which absorbs the visible spectrum is placed behind the glazing on a side opposite to that of the two digital optical devices.
18. The process according to claim 9 , wherein the glazing is a curved glazing.
19. The process according to claim 9 , wherein the at least two digital images are acquired when the mineral glass of the glazing is at a temperature between 300° C. and 1000° C. and the glazing is manufactured on a glass production line, the method further comprising detecting optical defects and/or aberration in the glazing with the determined three-dimensional geometry of the glazing.
20. A system for implementing a process according to claim 9 , said system comprising:
a projector configured to project a random light pattern onto a surface of a glazing based on transparent mineral glass;
at least two digital optical devices oriented at two different acquisition angles relative to a normal to the surface of the glazing, configured for simultaneous and independent acquisition of at least two digital images of the random light pattern;
a data processing unit for determining a three-dimensional geometry of a glazing based on a transparent mineral glass, said data processing unit using, as input data, a digital reference model of the three-dimensional geometry of the glazing, and the at least two digital images acquired by the digital optical devices, and providing, as output datum, a digital model of the three-dimensional geometry of the glazing;
said data processing unit comprising a non-transitory computer readable storage medium comprising instructions for implementing a method comprising the following steps:
(a) a step of anchoring the digital reference model to one of the at least two digital images by at least three anchoring points;
a step of calculating, based on the digital reference model, two virtual digital images of the glazing at the same two observation angles as those of the at least two digital images provided as input data;
a step of calculating residues corresponding to differences between the virtual images obtained in step (b) and the at least two digital images provided as input data;
a step of iterating steps (b) and (c), each iteration comprising a step of calculating a modified digital model based on a prior modified digital model provided as input datum for said step (d), so as to minimise the values of the residues until the the values are under a previously defined threshold value σ, the modified digital model then corresponding to the output datum.