# US 11,994,631 B2 · Calibration of LiDAR sensors

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- Number: US 11,994,631 B2
- Document ID: US11994631B2
- Status: Granted
- Kind: B2
- Application number: 17/069,727
- Filed: 2020-10-13
- Published: 2021-04-15
- Granted: 2024-05-28
- Earliest claimed: 2019-10-15
- Assignees: Cepton Technologies, Inc.
- Applicants: Cepton Technologies, Inc.
- Inventors: Dongyi Liao; Zukai Wang; Mark A. McCord; Chao Gu
- Web page: https://patentgrep.com/patent/US11994631B2

## CPC

- G01S 7/4972: {Alignment of sensor}
- G01B 11/0608: {Height gauges}
- G01S 7/4808: {Evaluating distance, position or velocity data}
- G01S 7/481: Constructional features, e.g. arrangements of optical elements
- G01S 7/4811: {common to transmitter and receiver}
- G01S 17/86: Combinations of lidar systems with systems other than lidar, radar or sonar, e.g. with direction finders
- G01S 17/89: for mapping or imaging
- G01S 17/894: Three-dimensional [3D] imaging with simultaneous measurement of time-of-flight at a two-dimensional [2D] array of receiver pixels, e.g. time-of-flight cameras or flash lidar
- G01S 17/931: of land vehicles
- G06T 7/80: Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration
- G06T 19/20: Editing of three-dimensional [3D] images, e.g. changing shapes or colours, aligning objects or positioning parts
- G05D 1/0231: {using optical position detecting means (position-fixing by using electromagnetic waves other than radio waves, e.g. optical position detecting means G01S5/16)}
- G05D 1/249: from positioning sensors located off-board the vehicle, e.g. from cameras
- G06T 2200/04: involving 3D image data
- G06T 2207/10028: Range image; Depth image; 3D point clouds
- G06T 2207/30204: Marker
- G06T 2207/30252: Vehicle exterior; Vicinity of vehicle
- G06T 2219/20: Indexing scheme for editing of 3D models
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G05D: SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES

## Abstract

A method of calibrating a LiDAR sensor mounted on a vehicle includes positioning the vehicle at a distance from a target including a planar mirror and features surrounding the mirror. The vehicle is positioned and oriented relative to the mirror so that an optical axis of the LiDAR sensor is nominally parallel to the optical axis of the mirror, and the target is nominally centered at a field of view of the LiDAR sensor. The method further includes acquiring, using the LiDAR sensor, a three-dimensional image of the target including images of the features of the target and a mirror image of the vehicle formed by the mirror. The method further includes determining a deviation from an expected alignment of the LiDAR sensor with respect to the vehicle by analyzing the images of the features and the mirror image of the vehicle in the three-dimensional image of the target.

## Claims

### Claim 1

A method of calibrating a LiDAR sensor mounted on a vehicle, the method comprising:
positioning the vehicle at a distance from a target, wherein:
the target comprises a planar mirror and features surrounding the planar mirror, an optical axis of the planar mirror being substantially horizontal;
the vehicle is positioned and oriented relative to the planar mirror so that an optical axis of the LiDAR sensor is nominally parallel to the optical axis of the planar mirror, and the target is nominally centered at a field of view of the LiDAR sensor;
acquiring, using the LiDAR sensor, a three-dimensional image of the target, wherein the three-dimensional image of the target includes images of the features of the target and a mirror image of the vehicle formed by the planar mirror; and
determining a deviation from an expected alignment of the LiDAR sensor with respect to the vehicle by analyzing the images of the features and the mirror image of the vehicle in the three-dimensional image of the target;
determining a position and an orientation of the LiDAR sensor relative to the target based on the images of the features;
determining a position and an orientation of the LiDAR sensor relative to the mirror image of the vehicle based on the mirror image of the vehicle; and
determining a transformation from a LiDAR coordinate system into a vehicle coordinate system based on: (i) the position and the orientation of the LiDAR sensor relative to the target, and (ii) the position and the orientation of the LiDAR sensor relative to the mirror image of the vehicle.

### Claim 2 (depends on 1)

The method of claim 1 further comprising:
re-calibrating the LiDAR sensor with respect to the vehicle based on the deviation from the expected alignment of the LiDAR sensor with respect to the vehicle.

### Claim 3 (depends on 1)

The method of claim 1 further comprising:
determining that the deviation from the expected alignment of the LiDAR sensor exceeds a threshold; and
providing an alert in response to determining that the deviation from the expected alignment of the LiDAR sensor exceeds the threshold.

### Claim 4 (depends on 1)

The method of claim 1 wherein the field of view of the LiDAR sensor is less than 180 degrees in a horizontal direction.

### Claim 5 (depends on 1)

The method of claim 1 wherein the LiDAR coordinate system has three translational degrees of freedom and three rotational degrees of freedom, and the vehicle coordinate system has three translational degrees of freedom and three rotational degrees of freedom.

### Claim 6 (depends on 5)

The method of claim 5 wherein:
the three translational degrees of freedom of the LiDAR coordinate system are along three orthogonal axes including an x-axis, a y-axis, and a z-axis, and the three rotational degrees of freedom of the LiDAR coordinate system include roll rotation around the x-axis, pitch rotation around the y-axis, and yaw rotation around the z-axis; and
the three translational degrees of freedom of the vehicle coordinate system are along three orthogonal axes including an X-axis, a Y-axis, and a Z-axis, and the three rotational degrees of freedom of the vehicle coordinate system include roll rotation around the X-axis, pitch rotation around the Y-axis, and yaw rotation around the Z-axis.

### Claim 7 (depends on 6)

The method of claim 6 further comprising determining, using two or more distance sensors positioned adjacent to the vehicle, a yaw angle of the vehicle with respect to the optical axis of the planar mirror.

### Claim 8 (depends on 7)

The method of claim 7 further comprising determining, using the two or more distance sensors, a lateral position of the vehicle along an axis that is orthogonal to the optical axis of the planar mirror and a vertical axis.

### Claim 9 (depends on 7)

The method of claim 7 wherein each of the two or more distance sensors comprises an ultrasonic sensor or a laser sensor.

### Claim 10 (depends on 6)

The method of claim 6 further comprising determining, using six distance sensors, a yaw angle, a roll angle, a pitch angle, and a translational position of the vehicle along three orthogonal axes in a coordinate system of the planar mirror.

### Claim 11 (depends on 10)

The method of claim 10 wherein each of the six distance sensors comprises an ultrasonic sensor or a laser sensor.

### Claim 12 (depends on 1)

The method of claim 1 wherein determining the deviation from the expected alignment of the LiDAR sensor with respect to the vehicle comprises:
storing a reference matrix relating to an expected relationship between the LiDAR sensor and the vehicle;
determining a matrix relating to a current relationship between the LiDAR sensor and the vehicle; and
determining the deviation from the expected alignment of the LiDAR sensor with respect to the vehicle by comparing the matrix to the reference matrix.

### Claim 13 (depends on 12)

The method of claim 12 further comprising re-calibrating the LiDAR sensor with respect to the vehicle based on the matrix relating to the current relationship between the LiDAR sensor and the vehicle.