Multi-modal calibration element for multi-sensor calibration

Abstract

The invention relates to a multi-modal calibration element (K) for multi-sensor calibration, consisting at least of a first individual element (1) and a second individual element (2), the first individual element (1) being designed to be sensed by a first sensor group comprising at least a camera sensor and a lidar sensor, and the second individual element (2) being designed to be sensed by a second sensor group comprising at least a radar sensor. The calibration element (K) is designed in such a way that it can be perceived by both sensor groups, the calibration element (K) being rotationally invariant about a z-axis of the calibration element (K).

Description

[0001] Multi-modal calibration element for multi-sensor calibration

[0002] The invention relates to a multi-modal calibration element for multi-sensor calibration and the use of such a calibration element in an arrangement for multi-sensor calibration.

[0003] Multi-sensor calibration elements are known from the state of the art, but currently they mostly focus on visual perception. Visual reference elements (e.g., a checkerboard or April tags on a board or plate) are used for camera and / or lidar calibration. Furthermore, checkerboard patterns or April tags must always be aligned toward the sensor.

[0004] Therefore, it is an object of the present invention to provide a multi-modal calibration element which enables reliable and precise calibration of several different sensors and is also cost-effective.

[0005] This object is solved by the subject matter of independent claims 1 and 5.

[0006] Further advantageous embodiments and embodiments are the subject of the subclaims.

[0007] Initial considerations were that large calibration elements would lead to inaccurate calibration results. A single board or plate would result in multiple lidar / radar detections, but it is unclear where a lidar / radar detection originates on the board. Therefore, small calibration elements are preferable for calibration accuracy.

[0008] Furthermore, elements on a board and around the z-axis are rotationally variable and must be completely visible in each sensor field of view in order to be used for calibration.

[0009] In order to additionally consider the radar as a sensor, the known state-of-the-art approaches always only use trihedral radar reflectors.

[0010] Trihedral radar reflectors again have the limitation of being dependent on the orientation of the individual sensor (rotational variation around the z-axis). Complex alignment to each individual sensor is essential. Moving around or through the calibration pattern, and thus dynamic calibration of the sensor system, is extremely limited.

[0011] According to the invention, a multi-modal calibration element for multi-sensor calibration is therefore proposed, consisting of at least a first and a second individual element, wherein the first individual element is configured for detection by a first sensor group comprising at least one camera sensor and one lidar sensor, and wherein the second individual element is configured for detection by a second sensor group comprising at least one radar sensor. The calibration element is configured such that it is perceptible by both sensor groups, wherein the calibration element is configured to be rotationally invariant about a z-axis of the calibration element.

[0012] The calibration element should be designed in such a way that it can be detected by any sensor, regardless of the sensor type. This requires at least two different individual elements of the calibration element, which differ particularly in their detectability by different sensor technologies. Due to the rotationally invariant design, the calibration element is perceived equally from all directions. Therefore, alignment to each individual sensor is completely avoided. Thus, dynamic and static calibration of a multimodal sensor system is enabled by the calibration element designed in this way.

[0013] In a particularly preferred embodiment, the individual elements are arranged such that the first individual element completely encloses the second individual element or that the first individual element is arranged below the second individual element.

[0014] In a preferred embodiment, the first individual element is designed as a cylinder or a surface element, and the second individual element is designed as an octahedral radar reflector. This embodiment is advantageous because the camera can detect the top surface of the cylinder or the surface element below the second individual element from all directions in the camera image. The surface element can be designed as a flat element, e.g., a disc, or as a marking directly on the roadway. A lidar sensor can detect the outer surface of the cylinder from all directions. A radar sensor detects the radar reflector in the cylinder from all directions.

[0015] In a further preferred embodiment, attributes of a cover surface and a lateral surface of the first individual element, or the attributes of the surface element and / or the size of the second individual element, are variable. The attributes include, in particular, the materials used, including their reflective properties, and / or the color of the cover surface and the color of the lateral surface.

[0016] The invention further proposes the use of a multimodal calibration element in an arrangement for multimodal sensor calibration, wherein the calibration element is configured according to one of the embodiments of the invention and wherein a plurality of calibration elements are used in the arrangement. The use of the multimodal calibration element with a calibration arrangement for a sensor system enables extrinsic, static, and dynamic calibration of a multimodal and monomodal sensor system of any sensor combination.

[0017] In a preferred embodiment of the use, the cover surface and the lateral surface of the first individual element or the surface element and / or the size of the second individual element of several calibration elements are identical and / or different in the plurality of calibration elements. Within the calibration arrangement, each calibration element is uniquely identifiable by means of the position coding. This enables color calibration in the camera by perceiving the color of the cover surfaces at different environmental positions of the calibration elements. Furthermore, amplitude calibration in the lidar sensor can be performed by different environmental positions of the calibration elements. In addition, radar cross-section RCS calibration in the radar is possible by the different environmental positions of the calibration elements. It would also be conceivable for all calibration elements to be designed differently.This enables color calibration in the camera by varying the color of the cover surfaces. Furthermore, amplitude calibration in the lidar sensor can be performed using differently colored lateral surfaces. Furthermore, radar cross-section RCS calibration in the radar is possible using radar reflectors of different sizes. Further advantageous configurations and embodiments are shown in the drawings. Therein:

[0018] Fig. 1 : a schematic representation of a multi-modal calibration element according to an embodiment of the invention;

[0019] Fig. 2: a further schematic representation of a multi-modal calibration element according to a further embodiment of the invention.

[0020] Figure 1 shows a schematic representation of a multi-modal calibration element according to one embodiment of the invention. The calibration element K comprises a first individual element 1 and a second individual element 2, wherein the second individual element 2 is arranged in the first individual element. The first individual element 1 is designed as a cylinder, which is cut open on one side surface in this illustration, and the second individual element 2 as an octahedral radar reflector. The first individual element 1 has a top surface 1a and a lateral surface 1b. A camera can capture the top surface 1a of the cylinder, a lidar sensor the lateral surface 1b, and a radar sensor the radar reflector.

[0021] Figure 2 shows a further schematic representation of a multi-modal calibration element according to a further embodiment of the invention. The calibration element K comprises a first individual element 1 and a second individual element 2, wherein the second individual element 2 is arranged below the first individual element. In this representation, the first individual element 1 is designed as a surface element. The first individual element 1 can be designed, for example, as a flat disk or as a marking on the roadway. The second individual element 2 is designed as an octahedral radar reflector. The first individual element 1 designed as a surface element can be recorded by a camera, similar to the top surface 1a of the cylinder from Figure 1. A lidar sensor can then record, for example, a lateral surface 2a of the radar reflector and a radar sensor can record the radar reflector itself.Thus, calibration of various sensors can also be ensured in this configuration. List of reference symbols.

[0022] 1 first individual element

[0023] 1a Cover surface of first individual element 1b Shell surface of first individual element

[0024] 2 second single element

[0025] 2a Shell surface of second individual element

[0026] K Calibration element

Claims

Patent claims 1 . Multi-modal calibration element (K) for multi-sensor calibration consisting of at least a first (1) and a second individual element (2), wherein the first individual element (1) is designed for detection by a first sensor group, comprising at least one camera sensor and one lidar sensor, and wherein the second individual element (2) is designed for detection by a second sensor group, comprising at least one radar sensor, characterized in that the calibration element (K) is designed such that it can be perceived by both sensor groups, wherein the calibration element (K) is designed to be rotationally invariant about a z-axis of the calibration element (K).

2. Multi-modal calibration element (K) according to claim 1, characterized in that the individual elements (1, 2) are arranged such that the first individual element (1) completely encloses the second individual element (2) or that the first individual element (1) is arranged below the second individual element.

3. Multi-modal calibration element (K) according to claim 2, characterized in that the first individual element (1) is designed as a cylinder or as a surface element and the second individual element (2) is designed as an octahedral radar reflector.

4. Multi-modal calibration element (K) according to claim 3, characterized in that Attributes of a cover surface (1 a) and a lateral surface (1 b) of the first individual element (1 ) or the attributes of the surface element and / or the size of the second individual element (2) are changeable.

5. Use of a multi-modal calibration element (K) in an arrangement for multi-modal sensor calibration, wherein the calibration element (K) is designed according to one of claims 1 to 4 and wherein a plurality of calibration elements (K) are used in the arrangement.

6. Use of a multi-modal calibration element (K) according to claim 5, characterized in that in the plurality of calibration elements (K) the cover surface (1a) and the Shell surface (1 b) of the first individual element (1 ) or the surface element and / or the size of the second individual element (2) of several Calibration elements (K) are designed the same and / or differently.

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