Multidimensional range mapping with pattern projection and cross correlation

• US 5,003,166 A
• Filed: 11/07/1989
• Issued: 03/26/1991
• Est. Priority Date: 11/07/1989
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Girod, Bernd
• Primary Examiner(s): Nelms, David C.
• Application Number:
  US07/432,788
• Time in Patent Office: 504 Days
• Field of Search: 250/201.6, 250/201.7, 250/201.4, 356/376, 356/371, 382/1, 382/32
• US Class Current: 250/201.4
• CPC Class Codes: G01B 11/2513 with several lines being projected in more than one direction, e.g. grids, patterns
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: G01S 17/89 for mapping or imaging

Abstract

A range camera is provided for the determination of range to an object through the utilization of a system which projects a limited depth of field light pattern onto an object and measures the blurring of the pattern on the object. In one embodiment an anisotropic aperture or astigmatic optics are used in combination with an isotropic pattern to eliminate system error introduced by the camera. The anisotropic aperture provides that blurring takes place only in a given direction, with measurement of blurring in an orthogonal direction providing an output only responsive to the blurring associated with the camera. This blurring can then be subtracted out to eliminate system error from the range measurement. The range camera is operative to produce a range picture or map, with optional outputs providing localized albedo and a conventional brightness image. In another embodiment, the direction of the blur, either in front of or in back of the plane of best focus of the projected pattern, is provided through the utilization of a mask having an aperture devoid of point symmetry. In a further embodiment, direction of blur can be ascertained through the utilization of astigmatic optics.

Claims

1. A multi-dimensional range mapping system, comprising:

means for optically projecting a limited depth of field pattern of light and dark areas having high spatial frequency onto an object for permitting determination of the range of surface patches on said object from a predetermined plane, with said pattern being focused to a plane of best focus; and

,

means including multi-dimensional cross correlation means for simultaneously determining the range of multiple surface patches on said object from said plane of best focus by measuring the degree of blur of said pattern on said object at said surface patch and for generating an instantaneous range mapping corresponding to the range of multiple surface patches on said object from said predetermined plane.

2. The system of claim 1 wherein said projecting means includes a projection system having large aperture optics.

3. The system of claim 2 wherein said projection system includes a slide projector and a slide carrying said pattern.

4. The system of claim 1 wherein said range determining means includes a camera having small aperture optics.

5. The system of claim 1 wherein said pattern is isotropic.

6. The system of claim 1 wherein said pattern includes a pseudo noise pattern.

7. The system of claim 1 wherein said pattern includes impulses.

8. The system of claim 1 wherein said pattern includes lines.

9. The system of claim 1 wherein said pattern includes a grid of lines.

10. The system of claim 9 wherein said grid is rectilinear.

11. The system of claim 1 wherein said range determining means includes a camera aimed at said object, said camera having an image plane.

12. The system of claim 11 wherein said camera includes means for providing an electronic reproduction of the image at said image plane, and wherein said range determining means includes means for storing said electronic reproduction of the image at said image plane and means for processing said stored image so as to generate signals corresponding to range and location of a surface patch on said object.

13. The system of claim 12 wherein said range determining means includes means for sampling the blur occurring at said surface patch in a predetermined slice thereacross and for generating corresponding data points, and means for ascertaining from said data points the standard deviation of the curve representing intensity vs. position across said slice.

14. The system of claim 12 and further including means for removing camera-induced blur from the range determination.

15. The system of claim 14 wherein said camera-induced blur removing means includes a projection system having an anisotropic aperture.

16. The system of claim 15 wherein said anisotropic aperture is effectively elongated in a predetermined direction and foreshortened in an orthogonal direction, and wherein said range determining system further includes means for sensing blur in each of said orthogonal directions and means for removing the effect of blur sensed in the direction orthogonal to the elongated aperture direction from said range determination, thereby removing camera-induced blur from the range measurement.

17. The system of claim 16 wherein said projection system includes a lens and wherein said anisotropic aperture includes a slotted mask at said lens.

18. The system of claim 17 wherein said slotted mask is oriented such that the slot is at an angle to the horizontal.

19. The system of claim 15 wherein said projection system includes an astigmatic lens system.

20. The system of claim 19 wherein said astigmatic lens system produces two planes of best focus and wherein said range determining system includes means for unambiguously ascertaining range based on measurement of blur of said surface patch relative to said two planes of best focus.

21. The system of claim 11 wherein said camera includes small aperture optics for maximizing the depth of field thereof.

22. The system of claim 11 and further including means coupled to said range determining means for ascertaining the albedo of said surface patch.

23. The system of claim 11 and further including means coupled to said range determining means for generating a conventional brightness image of said object.

24. The system of claim 1 wherein said pattern is a pseudo noise pattern and wherein said range determining means includes correlator means for providing an impulse having a width and corresponding to surface patch blur and means for measuring the width by said impulse.

25. The system of claim 1 wherein said pattern is formed from light in invisible regions of the electromagnetic spectrum.

26. The system of claim 25 wherein said pattern is formed from infrared light.

27. The system of claim 25 wherein said pattern is formed from ultraviolet light.