Method for determining optical property of calibration device, calibration device and method for calibrating camera

Abstract

The invention relates to a method for determining an optical property of a calibration device in relation to a camera to be calibrated. The calibration device comprises a laser facing in the direction of the camera to be calibrated and a diffractive optical element located between the camera and the laser, an autocollimator is provided which obtains autocollimator light and a laser beam reflected by the diffractive optical element via a beam splitter located in a beam path between the laser and the diffractive optical element. Determining an autocollimator light incident angle on the diffractive optical element by means of the autocollimator; a difference angle between the autocollimator light and the laser beam reflected by the diffractive optical element is determined by means of the autocollimator. Calculating a laser incident angle on the diffractive optical element according to the difference angle and an automatic collimator light incident angle on the diffractive optical element; the diffraction angle of the laser beam at the diffractive optical element is calculated by means of the laser incident angle. The invention also relates to a calibration device and to a method for calibrating a camera in a calibration device.

Description

Technical Field

[0001] The invention relates to a method for determining optical properties of a calibration device in relation to a camera to be calibrated. The invention also relates to a calibration device for carrying out such a method and a method for calibrating a camera in such a calibration device. Background Art

[0002] Cameras used in vehicles for driver assistance or automated driving systems have a variety of functions, including identifying objects in the scene using various object recognition algorithms. For many of these algorithms, the world-to-camera or camera-to-world transformation must be known, which means that the optical parameters of the camera must be known. These parameters include the focal length, principal point, and optical distortion parameters, such as radial and non-radial distortion parameters. Intrinsic calibration is the process of determining the optical distortion of a camera. A space-saving and cost-effective approach to camera calibration is based on the use of diffractive optical elements.

[0003] US Pat. No. 3,912,395 A discloses a method for calibrating distortion in an optical system. A collimated light beam is diffracted in various directions by means of a diffraction grating. The diffracted light emitted by the grating is then refocused by a calibrated optical system, thereby forming a sequence of images in the focal plane of the optical system. The relationship between the actual position of the image in the array and the position calculated for an undistorted system is a measure of the distortion present in the system.

[0004] DE 10 2022 104 717 A1 discloses a method for determining and correcting a central axis offset caused by the installation of an optical layer on a camera arrangement. In this case, the pixel position offset on a calibration target caused by the lens upstream of the camera arrangement is determined, resulting from the central axis offset caused by the window. A transformation is then generated accordingly, which corrects for the pixel position offset caused by the lens upstream of the camera arrangement, so that the pixel positions with the lens correspond to the pixel positions without the lens.

[0005] The object of the present invention is to specify a method for determining optical properties of a calibration device in relation to a camera to be calibrated, with which the accuracy of the camera calibration is increased.

[0006] This object is achieved by the method according to the invention. Preferred embodiments can be found in the following description. Summary of the Invention

[0007] The present invention provides a method for determining optical properties of a calibration device in relation to a camera to be calibrated. The calibration device comprises a laser oriented in the direction of the camera to be calibrated and a diffractive optical element located between the camera and the laser. An autocollimator is provided, which receives reflections of the autocollimator light and the laser beam from the diffractive optical element via a beam splitter located in the beam path between the laser and the diffractive optical element.

[0008] Optical properties are understood to be values of a calibration device that influence the accuracy of the camera being calibrated. A diffractive optical element is understood to be an element for shaping a light beam. Autocollimator light refers to the light beam emitted by the light source of the autocollimator.

[0009] The method according to the present invention includes the following steps: determining the angle of incidence of the autocollimator light on the diffractive optical element using the autocollimator; and determining the difference angle between the autocollimator light and the reflection of the laser beam from the diffractive optical element using the autocollimator. The method also includes the following steps: calculating the laser incident angle and the autocollimator light incident angle on the diffractive optical element from the difference angle; and calculating the diffraction angle of the laser beam at the diffractive optical element using the laser incident angle.

[0010] This accordingly determines which images must be received by the camera to be calibrated. Based on the images acquired by the camera and the computationally determined images, deviations can be determined with high precision. The camera can then be calibrated accordingly, thereby increasing the accuracy of camera calibration.

[0011] In a preferred embodiment of the present invention, the pitch, yaw, and rotation angles of a camera receiver configured on a camera mount are determined. In this case, the method includes the following steps: determining the angle of incidence of the autocollimator light on a mirror surface arranged in the camera receiver of the camera mount using an autocollimator; determining the angular deviation between the autocollimator light and the reflection of a laser beam from the mirror surface using the autocollimator; and calculating the laser beam incident angle on the mirror surface from the angular deviation and the autocollimator light incident angle. Furthermore, the method includes the following steps: calculating the pitch and yaw angles of the camera receiver using the laser beam incident angle on the mirror surface; determining the element rotation angle between the diffractive optical element and its element holder; and tactilely determining the holder rotation angle between the element holder and the camera receiver. In the final step of the method, the rotation angle of the diffractive optical element relative to the camera receiver is determined from the element rotation angle and the holder rotation angle.

[0012] The pitch angle is understood here to be the angle of motion of the camera about its transverse axis. The yaw angle describes the angle of motion about the camera's vertical axis. Correspondingly, the rotation angle specifies the angle of motion about the camera's longitudinal axis. A mirror is arranged in the camera holder instead of the camera. Here, the mirror is arranged in the camera holder in the same manner as the camera. Thus, the position of the camera in the holder can be simulated by the mirror. However, in contrast to the camera, the position of the mirror in the camera holder can also be determined by the autocollimator.

[0013] The tactile determination is performed using separate tactile measuring devices. These devices approach specific measuring points on the component holder and the camera receptacle. Based on the corresponding values, the rotation angle of the holder between the component holder and the camera receptacle can then be determined. By additionally determining the pitch, yaw, and roll angles of the camera receptacle, the position of the camera in space and relative to the diffractive optical element can be precisely determined. This specification allows the absolute orientation of the camera to be determined.

[0014] In another preferred embodiment of the present invention, the element rotation angle is determined by determining the angle between the actual reference line of the diffractive optical element or the reference line formed by the reference points relative to the actual reference line of the element holder or the reference line formed by the reference points. A reference line is understood to be an object shaped as a line, which is used to determine the rotation angle relative to another reference line with high precision. Here, the actual reference line is also constructed as a line at or on the fuselage. In contrast, the reference line formed by the reference points does not actually exist, but can be formed imaginarily by connecting these reference points. This reference line has the following advantages: it can be constructed with high precision and the angles between these reference lines can be determined in a simple way.

[0015] The autocollimator is preferably oriented so that the autocollimator light falls perpendicularly on the diffractive optical element. By orienting the autocollimator in this way, the calculation of the optical properties can be simplified.

[0016] In one advantageous development, the laser incident angle on the diffractive optical element is determined continuously. Thus, the laser incident angle is measured not only according to the configuration of the calibration device but also at predetermined time intervals during camera calibration. This allows for simple correction of variations in the laser incident angle, thereby improving the accuracy of camera calibration. Furthermore, by continuously measuring the laser incident angle, a rigid and expensive mechanical structure of the calibration device can be eliminated, allowing calibration to be performed economically and with high precision.

[0017] The object underlying the present invention is achieved by a calibration device for calibrating a camera. The calibration device has optical properties related to the camera, which can be determined according to the method according to the present invention. The calibration device comprises a camera holder for supporting the camera to be calibrated, a laser oriented in the direction of the camera to be calibrated, and a diffractive optical element located between the camera and the laser. Furthermore, the calibration device comprises an element holder for supporting the diffractive optical element, a beam splitter arranged between the diffractive optical element and the laser, and an autocollimator that receives reflections from the direction of the diffractive optical element via the beam splitter.

[0018] This calibration device essentially has the advantages and properties described above.

[0019] A diffractive optical element advantageously has at least one reference line and / or reference point. This reference line or reference point increases the accuracy of determining the element's rotation angle. This reference point can be established during the manufacture of the diffractive optical element. Since the manufacture of diffractive optical elements requires high precision, the reference point can be constructed with equally high precision during production.

[0020] In another advantageous embodiment, at least one reference line and / or reference point is formed on the component support. Such a reference line or reference point increases the accuracy of determining the component rotation angle, thereby also simplifying the determination of the component rotation angle.

[0021] According to a preferred embodiment, the reference lines and / or reference points are designed to be tactilely measurable. The reference points are advantageously designed as boreholes that enable tactile and optical determination. Alternatively, the reference points can also be designed as three-dimensional objects. This design of the reference lines and reference points simplifies tactile measurement of these elements.

[0022] According to another advantageous embodiment, the camera receptacle formed on the camera holder forms a reference surface. The reference surface is oriented so that the rotation of the camera receptacle can be determined via it. The reference surface advantageously extends so that its normal vector is orthogonal to the axis of rotation of the camera holder. The reference surface has the advantage of being easily detectable by touch. It is particularly advantageous if the reference surface forms part of the camera receptacle. The camera thus directly contacts the reference surface and has the same rotation as the reference surface. Thus, on the one hand, the reference surface forms the camera receptacle, and on the other hand, this surface also serves as a reference surface, eliminating the need for a separate surface.

[0023] The present invention also provides a method for calibrating a camera in a calibration device. The method includes the following steps: inserting the camera into a camera holder; recording an image generated in the camera by a laser beam diffracted at a diffractive optical element; and determining the pixel coordinates of image points generated by the diffracted laser beam. In a final step, the optical properties of the camera are determined based on the determined pixel coordinates and the diffraction angle of the diffracted laser beam, which is calculated based on the optical properties of the calibration device.

[0024] A diffracted laser beam is understood to be a laser beam that has been split into individual laser beams by a diffractive optical element. This laser beam has been diffracted by the diffractive optical element. In other words, the previously uniform laser beam has been split into a large number of individual laser beams. Pixel coordinates are understood to be the location of the pixel point generated by the diffracted laser beam on the camera's image sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Embodiments of the present invention will be illustrated in the accompanying drawings and explained in more detail in the following description. The accompanying drawings show:

[0026] Figure 1 A schematic diagram of a calibration device for calibrating a camera according to an embodiment of the present invention,

[0027] Figure 2 Illustration of the element holder and diffractive optical element,

[0028] Figure 3 Illustration of a camera mount with camera receptacle and mirror,

[0029] Figure 4 An embodiment of a method for determining optical properties of a calibration device,

[0030] Figure 5 An illustration of the camera with pitch, yaw, and roll angles, and

[0031] Figure 6 Embodiments of a method for calibrating a camera in a calibration device. DETAILED DESCRIPTION

[0032] exist Figure 1, a schematic diagram of a calibration device 10 for calibrating a camera 14 according to one embodiment of the present invention is shown. The calibration device 10 comprises a laser 18, which is oriented in the direction of the camera 14 to be calibrated. The laser beam 22 emitted by the laser 18 can be optically adjusted via a lens 26 downstream of the laser 18. A diffractive optical element 30 is arranged between the camera 14 and the laser 18. The calibration device 10 also has a beam splitter 34, which is located in the beam path between the laser 18 and the diffractive optical element 30. The reflection of the laser beam 22 at the diffractive optical element 30 can be transmitted via this beam splitter 34 to an autocollimator 38.

[0033] In the illustrated embodiment, the autocollimator 38 is arranged orthogonal to the beam path between the laser 18 and the diffractive optical element 30. The autocollimator light 42 is redirected via the beam splitter 34 so that it impinges on the diffractive optical element 30. Downstream of the diffractive optical element 30, a camera mount 46 is arranged, via which the camera 14 is supported.

[0034] Figure 2 The diagram shows an element holder 50 and a diffractive optical element 30. The diffractive optical element 30 is supported by the element holder 50. The element holder 50 is provided with a plurality of reference points 54 arranged perpendicularly to one another and a plurality of reference points 54 arranged horizontally to one another. In the present exemplary embodiment, the reference points 54 are designed as boreholes. The reference points 54 form an imaginary reference line 58. A rotation of the diffractive optical element 30 relative to the element holder 50 can be determined via this reference line 58. The diffractive optical element 30 is formed by a substrate 62 and an active surface 66 located on the substrate 62. Three crosses 70 arranged horizontally to one another are also provided on the substrate 62 and serve as reference points for the diffractive optical element 30. The outer edge 74 of the active surface 66 of the diffractive optical element 30 forms the reference line 74.

[0035] exist Figure 3 shows a diagram of a camera holder 46 with a camera receptacle 78 and a mirror 82. In the illustrated embodiment, the camera receptacle 78 is designed as a rectangular cutout in the camera holder 46 so that the camera 14 can be accommodated therein. The camera receptacle 78 is configured with four strips 86 that protrude into the camera receptacle 78. The strips 86 form defined contact surfaces for the camera 14. The camera receptacle 78 forms a reference surface 90, via which the holder rotation angle between the element holder 50 and the camera receptacle 78 can be tactilely determined. In the illustrated embodiment, the mirror 82 is arranged in the camera receptacle 78 instead of the camera 14. This mirror 82 allows the camera holder 46 and the camera receptacle 78 to be calibrated.

[0036] Figure 4 An embodiment of a method for determining optical properties of a calibration device 10 is shown. In a first step A of the method, the angle of incidence θ of the autocollimator light on the diffractive optical element 30 is determined by means of the autocollimator 38. To this end, the angle between the reflection of the autocollimator light 42 from the diffractive optical element 30 and the autocollimator light 42 emitted by the autocollimator 38 is determined. In a subsequent step B, the difference angle between the emitted autocollimator light 42 and the reflection of the laser beam 22 received by the autocollimator 38 is determined by the diffractive optical element 30 by means of the autocollimator 38.

[0037] In the following step C, the laser incident angle β on the diffractive optical element 30 is determined. To this end, the angle between the difference angle and the autocollimator light incident angle θ is determined. This angle corresponds to the laser incident angle β on the diffractive optical element 30. In the next step D, the diffraction angle of the laser beam 22 at the diffractive optical element 30 is calculated based on the laser incident angle β and the properties of the diffractive optical element 30.

[0038] In order to determine the orientation of the camera 14 in the calibration device 10, it is important to know the pitch angle γ, the yaw angle δ and the rotation angle ε. Figure 5 As shown, the pitch angle γ describes the angle around the transverse axis y of the camera 14. Here, the transverse axis y extends orthogonally to the longitudinal axis x and the vertical axis z of the camera 14. Figure 5 As shown, the yaw angle δ describes the angle about the vertical axis z of the camera 14 , while the rotation angle ε describes the angle about the longitudinal axis x of the camera 14 .

[0039] To determine the pitch angle γ and yaw angle δ of the camera receptacle 78 of the camera holder 46, in the next step E, the angle of incidence of the autocollimator light on the mirror 82 arranged in the camera receptacle 78 of the camera holder 46 is determined. To this end, the angle between the autocollimator light 42 emitted by the autocollimator 38 and the reflection of the autocollimator light 42 from the mirror 82 is determined using the autocollimator 38. Subsequently, in the next step F, the angular deviation between the autocollimator light 42 and the reflection of the laser beam 22 from the mirror 82 is determined using the autocollimator 38. In a further step G, the laser beam incident angle on the mirror 82 is determined from this angular deviation and the angle of incidence of the autocollimator light on the mirror 82. The pitch angle γ and yaw angle δ of the camera receptacle 78 can then be determined based on the laser beam incident angle.

[0040] To determine the rotation angle ε, in the next step I, the element rotation angle of the diffractive optical element 30 relative to the element holder 50 of the diffractive optical element 30 is determined. Here, the angle between an imaginary reference line formed by the reference point 70 of the diffractive optical element 30 and an imaginary reference line 58 is determined via the reference point 54 of the element holder 50. Similarly, the angle between a reference line formed by the outer edge 74 of the active surface 66 of the diffractive optical element 30 and a reference line formed by the reference line 58 of the element holder 50 can be determined. The determined angle corresponds to the element rotation angle of the diffractive optical element 30 relative to the element holder 50.

[0041] In the next step J, the holder rotation angle between the component holder and the camera receptacle 78 is determined by tactile determination. To this end, the reference point 54 of the component holder 50 and the reference surface 90 of the camera receptacle 78 are tactilely approached. In the next step K, the rotation angle ε of the diffractive optical element 30 relative to the camera receptacle 78 is determined from the component rotation angle and the holder rotation angle.

[0042] exist Figure 6 An embodiment of a method for calibrating a camera 14 in a calibration device 10 is shown in FIG. K In the next step B, the camera 14 is inserted into the camera bracket 46. K In the embodiment of the present invention, the image generated in the camera 14 is determined by means of a laser beam 22 emitted by the laser 18. Before entering the camera 14, the laser beam 22 is incident on the diffractive optical element 30 at a calculated laser incident angle β. The laser beam 22 is diffracted at the diffractive optical element 30 according to the incident angle β, and the diffracted laser beam 22 is then incident on the image sensor of the camera 14.

[0043] In another method step C K The pixel coordinates of the image point generated by the laser beam 22 are determined in the final step D K The optical properties of camera 14 are determined in [ ]. This process is performed based on the determined pixel coordinates and the previously determined optical properties of calibration device 10. To this end, the pixel coordinates that should be present are determined by calculation based on the optical properties of calibration device 10 and the known laser incident angle β. The optical properties of camera 14 are thus determined based on the calculated coordinates and the actual pixel coordinates.

Claims

1. A method for determining optical properties of a calibration device (10) in relation to a camera (14) to be calibrated, the calibration device (10) comprising a laser (18) oriented in the direction of the camera (14) to be calibrated and a diffractive optical element (30) located between the camera (14) and the laser (18), wherein: An autocollimator (38) is provided, the autocollimator obtaining reflections of the autocollimator light (42) and the laser beam (22) from the diffractive optical element (30) via a beam splitter (34) located in a beam path between the laser (18) and the diffractive optical element (30), the method comprising the following steps: - determining (A) the angle of incidence (θ) of the autocollimator light on the diffractive optical element (30) by means of the autocollimator (38), - determining (B) by means of the autocollimator (38) a difference angle between the autocollimator light (42) and a reflection of the laser beam (22) from the diffractive optical element (30), - calculating (C) the laser incident angle (β) on the diffractive optical element (30) from the difference angle and the autocollimator light incident angle (θ) on the diffractive optical element (30) - calculating (D) the diffraction angle of the laser beam (22) at the diffractive optical element (30) using the laser incident angle (β).

2. The method according to claim 1, characterized in that The pitch angle (γ), yaw angle (δ) and rotation angle (ε) of a camera receiving part (78) formed on a camera support (46) are determined, wherein the method comprises the following steps: - using the autocollimator (38), determining (E) an autocollimator light incidence angle on a mirror surface (82) arranged in a camera receiving element (78) of the camera holder (46), - determining (F) with the aid of the autocollimator (38) an angular deviation between the autocollimator light (42) and the reflection of the laser beam (22) from the mirror (82), - calculating (G) the laser incident angle on the mirror (82) from the angle deviation and the autocollimator light incident angle, - calculating (H) the pitch angle (γ) and the yaw angle (δ) of the camera receiving element (78) using the angle of incidence of the laser light on the mirror surface (82), - determining (I) an element rotation angle of the diffractive optical element (30) relative to an element holder (50) of the derivative optical element (30), - tactilely determining (J) the holder rotation angle between the element holder (50) and the camera receiving part (78), - determining (K) the rotation angle (ε) of the diffractive optical element (30) relative to the camera receiving part (78) from the element rotation angle and the support rotation angle.

3. The method according to claim 2, characterized in that The element rotation angle is determined by determining the angle between an actual reference line of the diffractive optical element (30) or a reference line (74) formed by a reference point (70) relative to an actual reference line of the element holder (50) or a reference line (54) formed by a reference point (58).

4. The method according to any one of the preceding claims, characterized in that An autocollimator (38) is oriented so that the autocollimator light (42) falls perpendicularly on the diffractive optical element (30).

5. The method according to any one of the preceding claims, characterized in that The incident angle (β) of the laser light on the diffractive optical element (30) is continuously determined.

6. A calibration device (10) for calibrating a camera (14), the calibration device having optical properties associated with the camera (14), the optical properties being determined according to the method according to any one of the preceding claims, the calibration device comprising: - a camera support (46) for supporting the camera (14) to be calibrated, - a laser (18) oriented in the direction of the camera (14) to be calibrated, - a diffractive optical element (30) located between the camera (14) and the laser (18), - an element holder (50) for supporting the diffractive optical element (30), a beam splitter (34) arranged between the diffractive optical element (30) and the laser (18), and - an automatic collimator (38) that obtains reflections from the direction of the diffractive optical element (30) via the beam splitter (34).

7. The calibration device (10) according to any one of the preceding claims, characterized in that The diffractive optical element (30) has at least one reference line (74) and / or reference point (70).

8. The calibration device (10) according to any one of the preceding claims, characterized in that At least one reference line (58) and / or reference point (54) is formed on the element carrier (50).

9. The calibration device (10) according to claim 8, characterized in that The reference line (58) and / or the reference point (54) are designed such that they can be measured tactilely.

10. The calibration device (10) according to any one of the preceding claims, characterized in that The camera receiving element (78) formed on the camera holder (46) forms a reference surface (90).

11. A method for calibrating a camera (14) in a calibration device (10) according to any one of claims 6 to 10, the method comprising the steps of: - Insert the camera (14) into (A K ) Camera bracket (46), - Shooting (B K ) an image produced in the camera (14) by the laser beam (22) diffracted at the diffractive optical element (30), - OK K ) is the pixel coordinate of an image point generated by the diffracted laser beam (22). - determining (D) from the determined pixel coordinates and the diffraction angle of the diffracted laser beam (22) determined by calculation according to any one of claims 1 to 5 based on the optical properties of the calibration device (10) K )The optical characteristics of the camera (14).

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