Method and device for determining the position, radius and/or shape deviation of a ring structure

• US 8,670,635 B2
• Filed: 11/09/2009
• Issued: 03/11/2014
• Est. Priority Date: 11/12/2008
• Status: Active Grant

• Current Assignee: EADS Deutschland GmbH (Airbus SE)
• Original Assignee: EADS Deutschland GmbH (Airbus SE)
• Inventors: Schertler, Klaus
• Primary Examiner(s): PATEL, KANJIBHAI B
• Application Number:
  US13/128,791
• Publication Number:
  US 20110262042A1
• Time in Patent Office: 1,583 Days
• Field of Search: 382/173, 382/197, 382/203, 382/280, 382/285, 382/286, 382/305, 382/312, 382/274, 342/351, 359/559, 359/577
• US Class Current: 382/280
• CPC Class Codes: G01J 3/45 Interferometric spectrometry
• CPC Class Codes: G01S 17/95 for meteorological use
• CPC Class Codes: G06T 7/62 of area, perimeter, diameter or volume
• CPC Class Codes: G06T 7/66 of image moments or centre of gravity
• CPC Class Codes: Y02A 90/10 Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

A system and method processes intensity images having a ring structure to measure position, shape deviation and/or radius of the ring structure, and to evaluate interferograms and/or localize objects. The system and method can define N sectors of the intensity image respectively having sector tips lying at a common sector origin within the ring structure, with N being a natural number where N>1, detect a distance of an intensity extreme from the respective sector tip of each sector of at least one group of the sectors to obtain a distance vector that includes the distances from all the sectors from at least the group of the sectors, perform a Fourier transformation of the distance vector, and determine a center, a radius and/or a deviation of the ring structure from a circular shape,-by using the first Fourier vector obtained by the Fourier transformation.

Claims

1. A method for processing an intensity image having a ring structure comprising:

defining N sectors of the intensity image, the N sectors having respective sector tips lying at a common sector origin within the ring structure, with N being a natural number where N>

1;

detecting a respective distance of an intensity extreme from the respective sector tip of each sector of at least one group of the sectors, in order to obtain a distance vector based on the respective distances for the sectors of the at least one group of sectors;

performing a Fourier transformation of the distance vector; and

determining a center of the ring structure based on a first Fourier vector obtained by the Fourier transformation.

2. The method as claimed in claim 1, wherein

the defining of N sectors comprises at least one of

dividing up the intensity image, into N radial image sectors,

consecutively allocating adjacent sectors a consecutive sector number n, where n=0. . . N−

1, and

in a case of an inexactly known center of the ring structure, defining an approximate ring center as a common sector origin (cx₀, cy₀) of the radial sectors which forms the respective sector tips.

3. The method as claimed in claim 1, wherein

the detecting of a respective distance for each of the respective sectors comprises

generating a 1-dimensional intensity vector from a 2-dimensional interferogram of the respective sector by 2D-1D transformation, which is selected such that intensity extremes present in the 2-dimensional interferogram appear equidistant in the 1-dimensional intensity vector;

performing a Fourier transformation on the 1-dimensional intensity vector;

determining at least one of a frequency position and a phase angle of a dominant frequency from a second Fourier vector obtained by the Fourier transformation of the 1-dimensional intensity vector; and

determining the respective distance of the respective intensity extreme from the sector tip in the sector by back calculation of the frequency position and the phase angle of the dominant frequency of the frequency domain in a spatial domain.

4. The method as claimed in claim 1, wherein

the performing of a Fourier transformation comprises

converting the distance vector D=(d₀, d₁, . . . d_N-1) by discrete Fourier transformation into a complex Fourier vector V=(v₀, v₁, . . . ,v_N-1), the values of the Fourier vector resulting from the values of the distance vector by the definition of the discrete Fourier transform as:

5. The method as claimed in claim 4, wherein the determining of the center of the ring structure comprises

determining the position of the ring center from the component v₁ of the first Fourier vector.

6. The method as claimed in claim 4, wherein the determining of the center of the ring structure comprises

determining coordinates cx, cy of the ring center according to equations:

cx=cx₀+2Re(v₁) and

cy=cy₀+2Im(v₁),

where

cx₀, cy₀ represent coordinates of a common sector origin defined by the defining of N sectors,

Re(v₁) represents a real part of the complex number v₁, and Im(v₁) represents an imaginary part of the complex number v₁.

7. The method as claimed in claim 4, wherein

the determining of the center of the ring structure comprises determining a ring radius of the ring structure from the Fourier vector component v₀, or from the Fourier vector component v₀ and at least one of the Fourier vector components v₁ and v₂.

8. The method as claimed in claim 7, further comprising

determining a mean radius from an absolute value |v₀| of the Fourier vector component v₀, and correcting the mean radius according to at least one of further Fourier vector components.

9. The method as claimed in claim 7, wherein

the ring radius of the ring structure is calculated from the Fourier vector components v₀, v₁ and v₂ according to a relationship:

10. The method as claimed in claim 1, further comprising

determining at least one of ring radii, ring centers and ring ellipticities in a Fabry-Perot interferometer based on at least one of the determined center of the ring structure, radius of the ring structure and deviation of the ring structure from a circular shape.

11. The method as claimed in claim 1, further comprising

repeating the defining, detecting, performing and determining with the determined center of the ring structure being used as the common sector origin for the sectors.

12. The method as claimed in claim 1, wherein

the defining of N sectors defines the sectors as mutually overlapping sectors.

13. The method as claimed in claim 1, wherein

the detecting of a respective distance is performed simultaneously in a plurality of the sectors.

14. The method as claimed in claim 1, wherein

the detecting of a respective distance comprises averaging intensity values acquired along a specific circular contour with a prescribed radius R_L or a specific elliptical contour with prescribed ellipse semi-axis lengths.

15. The method as claimed in claim 1, further comprising

calibrating an image processing device based on at least one of the determined position of the ring center and ellipticity of the ring structure.

16. The method as claimed in claim 1, further comprising

determining at least one of the following based on the determined at least one of the center of the ring structure, radius of the ring structure and deviation of the ring structure from a circular shape:

a change in length or wavelength,

gusts pertaining to an aircraft, and

a change in position of an object provided with a ring pattern, the ring pattern being recorded as an image and being subjected to corresponding image processing in order to acquire the position of the ring pattern, and thus the position of the object.

17. The method of claim 1, wherein the determining further comprises determining at least one of

a radius of the ring structure;

and

a deviation of the ring structure from a circular shape, based on the first Fourier vector obtained by the Fourier transformation.

18. The method as claimed in claim 17, wherein

the determining comprises determining an ellipticity of the ring structure based on at least one component of the first Fourier vector.

19. The method as claimed in claim 18, wherein

the ellipticity is calculated based on the Fourier vector component v₂ in the form of the numerical ellipticity ε

according to a relationship

20. The method as claimed in claim 17, further comprising

repeating the defining, detecting, performing and determining with the determined ellipticity of the ring structure being used as a starting point for averaging the intensity values along the specific circular or elliptical contour.

21. An apparatus for processing an intensity image having a ring structure, comprising:

a sector forming component configured to define N sectors of the intensity image, the N sectors having respective sector tips lying at a common sector origin within the ring structure, with N being a natural number where N>

1;

a distance acquiring component configured to acquire a respective distance of an intensity extreme from the respective sector tip of each sector of at least one group of the sectors, in order to obtain a distance vector based on the respective distances for the sectors of the at least one group of sectors;

a first Fourier transformation component configured to perform a Fourier transformation of the distance vector to obtain a first Fourier vector; and

a center acquiring component configured to determine a center of the ring structure from the first Fourier vector obtained by the Fourier transformation.

22. The apparatus as claimed in claim 21, wherein the sector forming component comprises at least one of the following:

a dividing component configured to divide up a given intensity image, into N radial image sectors,

an allocating component configured to consecutively allocate to adjacent sectors a consecutive sector number n, where n=0. . . N-1 and

a ring center selecting component configured to define an approximate ring center as a common sector origin (cx₀, cy₀) of the radial sectors, which forms the respective sector tips when the center of the ring structure is inexactly known.

23. The apparatus as claimed in claim 21, wherein the distance acquiring component includes:

an intensity vector generating component configured to generate a 1-dimensional intensity vector from a 2-dimensional interferogram of the respective sector by 2D-1D transformation, which is selected such that intensity extremes present in the 2-dimensional interferogram appear equidistant in the 1-dimensional intensity vector;

a second Fourier transformation component configured to perform a Fourier transformation on the 1-dimensional intensity vector to generate a second Fourier vector;

a determining component configured to determine at least one of a frequency position and phase angle of dominant frequency from the second Fourier vector obtained by the Fourier transformation of the 1-dimensional intensity vector; and

a distance determining component configured to determine the respective distance of the respective intensity extreme from the sector tip in the sector by back calculation of the frequency position and the phase angle of the dominant frequency of the frequency domain in a spatial domain.

24. The apparatus as claimed in claim 21, wherein

the first Fourier transformation component is configured to convert the distance vector D=(d₀, d₁, . . . ,d_N-1) by discrete Fourier transformation into a complex Fourier vector V=(v₀, v₁, . . . ,v_N-1), the values of the Fourier vector resulting from the values of the distance vector by the definition of the discrete Fourier transform as:

25. The apparatus as claimed in claim 24, wherein

the center acquiring component is configured to determine the position of the ring center from the component v₁ of the first Fourier vector.

26. The apparatus as claimed in claim 24, wherein the center acquiring component is configured to determine the coordinates cx, cy of the ring center according to equations:

cx=cx₀+2Re(v₁) and

cy=cy₀+2Im(v₁),

where

cx₀, cy₀ represent coordinates of the common sector origin,

Re(v₁) represents a real part of the complex number v₁, and

Im(v₁) represents an imaginary part of the complex number v₁.

27. The apparatus as claimed in claim 21, wherein

at least one of the center acquiring component, a radius acquiring component and a shape deviation acquiring component are configured to calculate at least one of ring radii, ring centers and ring ellipticities in a Fabry-Perot interferometer based on at least one of the determined center of the ring structure, radius of the ring structure and deviation of the ring structure from a circular shape.

28. The apparatus as claimed in claim 21, wherein

the sector forming component is configured to use the determined center of the ring structure as the common sector origin for the sectors when repeating an operation to again define the sectors.

29. The apparatus as claimed in claim 21, wherein

the sector forming component is configured to define the sectors as mutually overlapping sectors.

30. The apparatus as claimed in claim 21, further comprising

a plurality of the distance acquiring components that are configured to simultaneously acquire respective distances of a intensity extremes from the respective sector tips of the respective sectors.

31. The apparatus as claimed in claims 21, wherein

the distance acquiring component includes an averaging component that is configured to average intensity values acquired along a specific circular contour with a prescribed radius R_L or specific elliptical contour with prescribed ellipse semi-axis lengths.

32. The apparatus as claimed in claim 31, wherein

the averaging component is configured to use a previously acquired position and shape of the ring structure as a starting point for averaging along the correct circular or elliptical contour.

33. The apparatus as claimed in claim 21, further comprising

a calibration component configured to calibrate the apparatus based on initial values obtained by at least one of the center acquiring component, a radius acquiring component and a shape deviation acquiring component.

34. The apparatus as claimed in claim 21, wherein

the at least one of the center acquiring component, the radius acquiring component and the shape deviation acquiring component are configured to determine at least one of the following based on the determined at least one of the center of the ring structure, radius of the ring structure and deviation of the ring structure from a circular shape:

a change in length or wavelength,

gusts pertaining to an aircraft, and

a change in position of an object provided with a ring pattern, the ring pattern being recorded as an image and being subjected to corresponding image processing in order to acquire the position of the ring pattern, and thus the position of the object.

35. The apparatus of claim 21, further comprising at least one of

a radius acquiring component configured to determine a radius of the ring structure from the first Fourier vector obtained by the Fourier transformation, and

a shape deviation acquiring component configured to acquire a deviation of the ring structure from a circular shape based on the first Fourier vector acquired by the Fourier transformation.

36. The apparatus as claimed in claim 35, wherein

the radius acquiring component is configured to determine a ring radius of the ring structure from the Fourier vector component v₀, or from the Fourier vector component v₀ and at least one of the Fourier vector components v₁ and v₂.

37. The apparatus as claimed in claim 36, wherein

the radius acquiring component is configured to determine a mean radius from an absolute value |v₀| of the Fourier vector component v₀, and to determine the radius by correcting the mean radius by according to at least one of further Fourier vector components.

38. The apparatus as claimed in claim 36, wherein

the radius acquiring component is configured to calculate the radius of the ring structure from the Fourier vector components v₀, v₁ and v₂ according to a relationship:

39. The apparatus as claimed in claim 35, wherein

the shape deviation acquiring component is configured to determine an ellipticity of the ring structure based on at least one component of the first Fourier vector.

40. The apparatus as claimed in claim 39, wherein

the shape deviation acquiring component is configured to calculate the ellipticity from the Fourier vector component v₂ as a numerical ellipticity ε

according to a reslationship