Evaluation of projection pattern for transitions in pattern to determine spatial structure of 3D surfaces

• US 6,495,848 B1
• Filed: 11/30/2000
• Issued: 12/17/2002
• Est. Priority Date: 05/14/1998
• Status: Active Grant

• Current Assignee: Orametrix GmbH
• Original Assignee: Orametrix Incorporated
• Inventors: Rubbert, Rüdger
• Primary Examiner(s): Allen, Stephone B.
• Assistant Examiner(s): HILL, BRADFORD K
• Application Number:
  US09/673,963
• Time in Patent Office: 747 Days
• Field of Search: 250/559.19, 250/559.22, 250/559.04, 356/603, 356/610, 356/625, 356/3.03, 382/174
• US Class Current: 250/559.22
• CPC Class Codes: G06T 2207/30004 Biomedical image processing
• CPC Class Codes: G06T 7/521 from laser ranging, e.g. using interferometry; from the projection of structured light

Abstract

The present invention concerns a process for detecting the spatial structure of a three-dimensional surface by projection of a pattern on to the surface along a projection direction which defines a first axis, and by pixel-wise detection of at least one region of the pattern projected on to the surface, by means of one or more sensors in a viewing direction of the sensor or sensors, which defines a second axis, wherein the first and the second axes (or a straight line parallel to the second axis) intersect at an angle different from 0° so that the first and the second axes (or the straight line parallel thereto) define a triangulation plane, wherein the pattern is defined at least upon projection into a plane perpendicularly to the first axis by a varying physical parameter which can be detected by the sensor (sensors), and wherein the pattern is such that the difference in the physically measurable parameter, measured between predeterminable image pixels or pixel groups, along a predeterminable pixel row which is preferably parallel to the triangulation plane, assumes at least two different values. In order to provide a process for detecting the spatial structure of a three-dimensional surface, which is substantially independent of different inclinations with respect to a normal to the triangulation plane and also independent of the other surface properties which independently of the spatial extent of the surface can influence the physical parameter to be measured, in accordance with the invention it is proposed that, for the purposes of evaluation of the imaged pattern structure only changes in the physical parameter between the predetermined pixels or predetermined pixel groups of one or more pixel rows which are preferably parallel to the triangulation plane are detected and converted into spatial co-ordinates of the surface.

Claims

1. A process for detecting the spatial structure of a three-dimensional surface comprising the steps of:

(a) projecting a pattern onto the surface along a projection direction which defines a first axis,

(b) pixel-wise detecting of at least one region of the pattern projected onto the surface, by means of one or more sensors in a viewing direction of the sensor or sensors, said viewing direction defining a second axis, wherein the first and the second axis (or a straight line parallel to the second axis) intersect at an angle different from 0°

so that the first and the second axes (or a straight line parallel thereto) define a triangulation plane,

(c) wherein the pattern is defined upon projection into a plane perpendicular to the first axis by a varying physical parameter which can be detected by the sensor (or sensors), and wherein the pattern is such that the difference in the physically measurable parameter, measured between predetermined image pixels or pixel groups, along a predeterminable pixel row which is parallel to the triangulation plane, assumes at least two different values including smooth and abrupt transitions from one value to another,

(d) evaluating of the imaged pattern structure by only evaluating changes in the physical parameter between the predetermined pixels or predetermined pixel groups of one ore more pixel rows which are parallel to the triangulation plane and converting such predetermined pixels or predetermined pixel groups associated with said changes in the physical parameter into a binary pattern and using said binary pattern to determine spatial coordinates of the surface.

2. process as set forth in claim 1 characterised in that the difference in the physically measurable parameter between respective adjacent pixels or pixel groups is ascertained along a predetermined direction.

3. A process as set forth in claim 1 characterised in that pixels, which are disposed in mutually superposed relationship in a column of a plurality of parallel pixel rows are assembled to form a pixel group, and the changes in the physical parameter are evaluated between respective ones of such adjacent pixel groups.

4. A process as set forth in claim 1 characterised in that the pattern is an encoded pattern in which various pattern regions of an adequate size are distinguishable from each other and are fixed in respect of their position within the overall pattern.

5. A process as set forth in claim 4 characterised in that for pattern encoding and identification of the position of pattern elements, only changes are evaluated which are greater than the changes between adjacent pixels or pixel groups within the pattern elements where there are at least two types of pattern elements, in the surface region of with the measurable physical parameter is respectively of an almost constant value, wherein the value of said physical parameter clearly measurably differs between the two types of pattern elements.

6. A process as set forth in claim 1 characterised in that the pattern is formed from pattern elements which each occupy approximately equal size surface areas in a plane perpendicular to the projection direction.

7. A process as set forth in claim 6 characterised in that there are provided at least two types of pattern elements, in the surface region of which the measurable physical parameter is respectively of an almost constant value, wherein the value of said physical parameter clearly measurably differs between the two types of pattern elements.

8. A process as set forth in claim 7 characterised in that there is provided at least one type of a pattern element in which the value of the physical parameter substantially continuously changes at least within a part of its surface region along a predetermined direction.

9. A process as set forth in claim 6 characterised in that there is provided at least one type of a pattern element in which the value of the physical parameter substantially continuously changes at least within a part of its surface region along a predetermined direction.

10. A process as set forth in claim 9 characterised in that there are provided at least two types of pattern elements which differ by the sign of the change in the physical parameter within the surface region thereof and along the predetermined direction.

11. A process as set forth in claim 4 characterised in that the various types of pattern elements are arranged in an encoded distribution on the surface of the projected pattern.

12. A process as set forth in claim 4 characterised in that the various types of pattern elements are distributed in a random arrangement over the projected surface.

13. A process as set forth in claim 6 characterised in that the surface region of a pattern element in the imaging plane corresponds to an area of m×

n pixels with m, n≧

2 and m<

<

M and n<

<

N, wherein M×

N is the total number of detected image pixels.

14. A process as set forth in claim 4 characterised in that for pattern encoding and identification of the position of pattern elements, only changes are evaluated which are greater than the changes between adjacent pixels or pixel groups within the pattern elements which occupy approximately equal-size surface areas in a plane perpendicular to the projection direction.

15. A process as set forth in claim 1 characterised in that for detecting the spatial structure of the three-dimensional surface at least two measurements with triangulation planes which are angled relative to each other are implemented and combined together.