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WO2005122090A1 - Procede d'etalonnage d'une camera - Google Patents

Procede d'etalonnage d'une camera Download PDF

Info

Publication number
WO2005122090A1
WO2005122090A1 PCT/DE2005/001001 DE2005001001W WO2005122090A1 WO 2005122090 A1 WO2005122090 A1 WO 2005122090A1 DE 2005001001 W DE2005001001 W DE 2005001001W WO 2005122090 A1 WO2005122090 A1 WO 2005122090A1
Authority
WO
WIPO (PCT)
Prior art keywords
camera
calibration pattern
calibration
image
angle
Prior art date
Application number
PCT/DE2005/001001
Other languages
German (de)
English (en)
Inventor
Dirk Ulbricht
Matthias Zobel
Markus Spitzer
Original Assignee
Adc Automotive Distance Control System Gmbh
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Adc Automotive Distance Control System Gmbh filed Critical Adc Automotive Distance Control System Gmbh
Priority to DE112005001188T priority Critical patent/DE112005001188A5/de
Publication of WO2005122090A1 publication Critical patent/WO2005122090A1/fr

Links

Classifications

    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00—Image analysis
    • G06T7/80—Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration

Definitions

  • the invention relates to a method for calibrating a camera which is arranged in a motor vehicle.
  • Cameras which are arranged in the motor vehicle are generally used to record the roadway and all other relevant objects.
  • the evaluation of a camera image is usually carried out via a computer unit, likewise arranged in the motor vehicle, with which the intended functions are calculated and controlled.
  • the cameras installed in the motor vehicle In order for the cameras installed in the motor vehicle to function properly and accurately, they have to be positioned and aligned exactly so that no errors are included in the evaluation of the camera image that affect control functions later.
  • the position of the camera in the motor vehicle which is composed of the three spatial coordinates, and the orientation of these must be determined. Since the tolerances that occur in vehicle manufacture are comparatively large, a camera cannot simply be calibrated by installing it at a designated position, but must be individually calibrated or aligned after it has been installed in the motor vehicle.
  • the position calculation of a camera can be carried out comparatively simply by the position of one or more reference points of the camera with respect to the
  • a calculation of these angular deviations from the nominal angles on the basis of a number of reference points of the camera is problematic since the dimensions of the camera are comparatively small and an exact measurement can therefore only be carried out with a very high outlay. Furthermore, it is possible that a camera also has manufacturing tolerances that cause a deviation from the target orientation, but cannot be registered by measuring from the outside.
  • the invention is therefore based on the object of specifying a method for calibrating a camera in a motor vehicle. ben, with which the deviation angle of a camera to target arrangement angles can be determined particularly easily.
  • This object is achieved according to the invention in that, in order to calibrate a camera which is arranged in a motor vehicle, the angle of deviation of the camera from the nominal arrangement angles is determined by a camera image of a rectangular calibration pattern arranged outside the motor vehicle.
  • the invention is based on the consideration that a camera image of the camera should best be used for a simple calibration of a camera, since in this way possible manufacturing tolerances of the camera and possible manufacturing tolerances of relevant motor vehicle components need not be determined and taken into account. Furthermore, the invention is based on the consideration that a camera image of an object whose position relative to the motor vehicle and also to the camera is known should be used to determine the alignment angle. In addition, the geometry and the extent of the recorded object should be known in order to use the embodiment as a reference.
  • a rectangular calibration pattern is particularly useful since the camera image of a rectangular object changes when the roll, yaw and pitch angle deviates from the corresponding target angle compared to a reference target image, and these deviations change because of the 90 ° angle of the calibration pattern is comparatively easy to detect.
  • the possibility of being able to determine the position of the camera and that of the calibration pattern with respect to the motor vehicle is a prerequisite for the function of the method.
  • the positioning of the calibration pattern to the motor vehicle or the positioning of the camera installed in the motor vehicle to the calibration pattern can be carried out comparatively precisely by calibrating a camera in a test stand, such as a chassis adjustment stand, where the chassis geometry is very precisely can be measured. In such a test bench, the motor vehicle is usually guided in rolls and the motor vehicle position can thus be reproduced relative to the calibration pattern.
  • a corresponding test bench can also be integrated into a production line.
  • a number of calibration markings are advantageously used for the calibration pattern, which are arranged in a rectangular formation and thus form the rectangular calibration pattern. If more than four markings are used to form the calibration pattern, distortions in the camera image can preferably be compensated for.
  • the calibration pattern For a simple implementation of the calibration pattern, exactly four calibration marks are expediently used, one calibration mark forming a corner of the rectangular calibration pattern.
  • the calibration marks are designed in such a way that they reflect ambient light.
  • the calibration markings can have a particularly reflective surface for a particularly high contrast to the surroundings. Irradiation of the calibration markings with light is also conceivable in order to increase the contrast with the surroundings.
  • the calibration markings preferably actively emit light.
  • the calibration marks on the camera appear brighter than the light from the backscattering surfaces of the surroundings.
  • the image is darkened, only the desired calibration markings can be used by the camera to calibrate the camera.
  • reflections and contours of the contours of the motor vehicle or other painted, glass and reflective surfaces can be suppressed.
  • infrared light is advantageously used. This is possible because, unlike the human eye, a camera is sensitive to infrared radiation and can detect the calibration markings emitting the light. When using infrared light, impairment of the surrounding people can be prevented, so that these tasks, such as manufacturing tasks on the motor vehicle, can be carried out unimpeded.
  • the determination of the deviation angle of the camera from the desired arrangement angles is expediently carried out from the deviation position of the rectangular sides and diagonals of the calibration pattern from the respective desired position in the camera image.
  • the deviation angles are the roll, yaw and pitch angles of the camera with respect to the target orientation of the respective coordinate.
  • the rectangle sides are in each case rotated or tilted by a certain angle in comparison to nominal rectangle sides or the image edge.
  • the center point of the calibration pattern which results from the diagonal intersection of the rectangular pattern, is vertically and / or horizontally shifted in the camera image with respect to the image center.
  • the horizontal distance of the diagonal intersection of the calibration pattern from the center of the image is therefore preferably used to calculate a yaw angle of a camera.
  • the yaw angle is advantageously approximately calculated from the arc tangent of the quotient from the horizontal distance of the diagonal intersection of the calibration pattern from the center of the image minus a transverse offset coefficient and the focus length of the camera.
  • the cross offset coefficient represents the displacement of the diagonal intersection of the calibration pattern from the center of the image, which is caused by a cross offset, parallel to the plane of the calibration pattern, of the camera with respect to the calibration pattern. ters occurs. If the camera is arranged directly opposite the calibration pattern, the transverse offset coefficient disappears or is zero and the horizontal deviation of the diagonal intersection from the center of the image that can be observed at a yaw angle only occurs due to the existing angular displacement of the camera.
  • the transverse offset coefficient is expediently calculated approximately from the product of the transverse displacement of the solder by the camera onto the level of the calibration pattern and the quotient of the focus length of the camera and the distance of the camera lens from the level of the calibration pattern.
  • the pitch angle is determined analogously to the calculation of the yaw angle.
  • the vertical distance of the diagonal intersection of the calibration pattern from the center of the image is preferably used to calculate the angle.
  • the product of the length of the solder is advantageously reduced to the level of the
  • Calibration pattern approximately calculated by the camera and the tangent of the quotient from the vertical distance of the diagonal intersection of the calibration pattern from the center of the image minus a vertical offset coefficient and the focus length of the camera.
  • the vertical coefficient which describes the vertical displacement of the camera with respect to the calibration pattern, is expediently calculated from the product of the vertical displacement of the solder by the camera on the level of the calibration pattern and the quotient of the focus length of the camera and the distance of the camera lens from the level of the calibration pattern ,
  • the roll angle or roll angle with which the camera is installed can be determined by rotating the rectangular sides of the calibration pattern in the camera image.
  • a roll angle is advantageously approximately calculated from an average of the angle of the four rectangular sides of the calibration pattern in the camera image to the adjacent image edges.
  • the calibration method described above is expediently used in a production line, the calibration markings being positioned to the side or above the production line.
  • the calibration markings can be arranged rigidly on columns positioned on the side of the production line or on a portal.
  • the motor vehicles can thus be transported or driven past the calibration markings.
  • the process is preferably carried out by a control device.
  • the advantages of the invention are, in particular, the possibility of performing a calibration of a camera which is arranged in a motor vehicle comparatively quickly and easily.
  • the necessary determination or approximate calculation of the alignment angle of the camera is based on the evaluation of only one camera image of calibration markings, so that the technical expenditure for calibration can be kept low.
  • the computation algorithms required for determining the alignment angle are comparatively little computation-intensive, so that the calibration method can be implemented on a suitable control device.
  • Another advantage of the method is the possibility of using the method in a production line for motor vehicles, so that cameras installed in the motor vehicle can still be calibrated during series production and this is not carried out in a subsequent process. As a result, the total production time or the throughput time of a motor vehicle can be reduced.
  • FIG. 1 schematically shows the arrangement of a calibration device for a camera installed in a motor vehicle
  • FIG. 2 shows a camera image of a calibration pattern of a camera which is installed with a yaw angle (psi), a pitch angle (theta) and a roll angle (phi), and
  • FIG. 3 shows a camera image of a calibration pattern for determining a roll angle (phi) of a camera.
  • FIG. 1 the section of a production line for a motor vehicle 1 or a motor vehicle series is shown schematically.
  • a number of motor vehicles 1 or the resulting motor vehicles 1 pass through a production line, the motor vehicle 1 being machined or components being added by tools positioned at the edge of the line.
  • a camera 2 is installed in the motor vehicle 1 to be manufactured and is to be used for automatic control functions of the motor vehicle 1. In order to align or calibrate the camera 2 for high accuracy, it is calibrated during the manufacturing process of the motor vehicle 1 or deviation angles with respect to the target arrangement angles are determined.
  • the section of the production line shown in FIG. 1 shows the calibration Device for a camera 2 already installed in the motor vehicle 1.
  • the camera 2 is calibrated by evaluating a camera image of a calibration pattern 8.
  • a rectangular calibration pattern 8 is used, which is formed by four calibration marks 6.
  • the calibration markings 6 are arranged on a portal 4 of the production line, so that a motor vehicle 1 can be transported through the portal 4.
  • the calibration markings 6 actively emit infrared light. It can be avoided that the strip workers employed on the production line are dazzled by the light, but that this can be detected by the camera 2.
  • the Kalibriermu- the 'edge 8 forming calibration marks 6 and not the infrared light reflecting surrounding surfaces is darkened, the camera image accordingly.
  • the position of the camera 2 installed in the motor vehicle with respect to the calibration markings 6 must first be determined. Since the position of the calibration markings 6 is known, only the spatial position of the camera 2 in the motor vehicle 1 and the relative position of the motor vehicle 1 relative to the calibration markings 6 need to be determined.
  • the position of the camera 2 is within the
  • the production line is measured with a chassis measurement. solution device 10 provided. The entire calibration process is carried out automatically by the control device 12.
  • the determination of the yaw and pitch angle is calculated from the position of the diagonals of the calibration pattern 8 in the camera image that deviates from the desired position.
  • the horizontal and vertical deviation from the center of the image is determined via the intersection of the diagonals.
  • the horizontal distance ⁇ x of the diagonal intersection of the calibration pattern 8 from the center of the image, which is shown in FIG. 2, is then used for the approximate calculation of a yaw angle of the camera 2. If the camera 2 is positioned directly opposite the calibration pattern 8 or has no transverse offset with respect to the calibration pattern 8, the yaw angle psi is approximately calculated as: wherein ⁇ xi mage the length of the projection onto the imager (image chip of the camera) of the horizontal distance of the point of intersection of the calibration Diagonalen- 8 from the center of the image and f is the focal length of the camera 2 is.
  • the determination of the pitch angle is carried out analogously to the calculation of the yaw angle, so that 2 n is approximately the same for a pitch angle of the camera
  • ⁇ yi mage is the vertical distance of the diagonal intersection of the calibration pattern 8 from the center of the image, measured on the imager, and y came to be the vertical displacement of the solder by the camera 2 onto the plane of the calibration pattern 8.
  • the roll angle phi or roll angle phi, with which the camera 2 is installed, can be determined via the rotation of the
  • Rectangular sides of the calibration pattern 8 are made in the camera image, as shown in FIG. 3.
  • the angles cp 1 # ⁇ 2 r ⁇ 3 r 9 4 represent the angles with which the rectangular sides of the calibration pattern 8 are rotated relative to the adjacent image edges of the camera 2.

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Vision & Pattern Recognition (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Length Measuring Devices By Optical Means (AREA)

Abstract

L'objet de la présente invention est la mise au point d'un procédé d'étalonnage d'une caméra (2) installée dans un véhicule à moteur (1) selon lequel les angles de déviation de la caméra (2) par rapport à des angles de positionnement théoriques sont particulièrement faciles à déterminer. A cet effet, les angles de déviation de la caméra (2) par rapport aux angles de positionnement théoriques sont approximativement déterminés sur la base d'une image, prise par la caméra, d'un motif d'étalonnage rectangulaire (8) situé à l'extérieur du véhicule à moteur (1).
PCT/DE2005/001001 2004-06-05 2005-06-03 Procede d'etalonnage d'une camera WO2005122090A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
DE112005001188T DE112005001188A5 (de) 2004-06-05 2005-06-03 Verfahren zur Kalibrierung einer Kamera

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
DE102004027613.7 2004-06-05
DE102004027613 2004-06-05
DE102004033468.4 2004-07-10
DE102004033468A DE102004033468A1 (de) 2004-06-05 2004-07-10 Verfahren zur Kalibrierung einer Kamera

Publications (1)

Publication Number Publication Date
WO2005122090A1 true WO2005122090A1 (fr) 2005-12-22

Family

ID=34971286

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/DE2005/001001 WO2005122090A1 (fr) 2004-06-05 2005-06-03 Procede d'etalonnage d'une camera

Country Status (2)

Country Link
DE (2) DE102004033468A1 (fr)
WO (1) WO2005122090A1 (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2009056050A1 (fr) * 2007-10-24 2009-05-07 Shenzhen Huawei Communication Technologies Co. , Ltd. Procédé et dispositif d'étalonnage de caméra vidéo
WO2009089932A1 (fr) * 2008-01-15 2009-07-23 Robert Bosch Gmbh Procédé de réglage d'image destiné à une image vidéo
WO2014029720A1 (fr) * 2012-08-20 2014-02-27 Johnson Controls Gmbh Procédé d'étalonnage d'une caméra à temps de vol
CN104504680A (zh) * 2014-11-23 2015-04-08 北京联合大学 一种用于智能车的逆透视标定方法
CN111973134A (zh) * 2020-08-06 2020-11-24 江苏势通生物科技有限公司 基于视觉的测试体对准待测通道的方法、导航方法及系统

Families Citing this family (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2986358B1 (fr) 2012-01-31 2014-03-07 Continental Automotive France Procede de calibration des caracteristiques extrinseques d'une camera solidaire d'un pare-brise de vehicule automobile
DE102013103952B4 (de) 2012-05-02 2020-07-09 GM Global Technology Operations LLC Spurerkennung bei voller Fahrt mit einem Rundumsichtsystem
DE102013103953B4 (de) 2012-05-02 2020-07-09 GM Global Technology Operations LLC Spurerkennung bei voller Fahrt unter Verwendung mehrerer Kameras
JP5947268B2 (ja) * 2013-09-20 2016-07-06 本田技研工業株式会社 車両のロール角推定装置
EP3174007A1 (fr) 2015-11-30 2017-05-31 Delphi Technologies, Inc. Procédé pour étalonner l'orientation d'une caméra montée sur un véhicule
DE102017207614A1 (de) * 2017-05-05 2018-11-08 Conti Temic Microelectronic Gmbh Vorrichtung und Verfahren zur Kalibrierung eines Kamerasystems eines Fahrzeugs
EP3534333A1 (fr) 2018-02-28 2019-09-04 Aptiv Technologies Limited Procédé d'étalonnage de la position et de l'orientation d'une caméra par rapport à un motif d'étalonnage
CN109358338B (zh) * 2018-11-23 2020-09-29 北京经纬恒润科技有限公司 一种车辆标定方法及系统
DE102019003906A1 (de) 2019-06-03 2020-01-02 Daimler Ag Verfahren zum Kalibrieren von zumindest zwei optischen Erfassungseinrichtungen eines Kraftfahrzeugs, sowie Kalibrierungssystem

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1120746A2 (fr) * 2000-01-27 2001-08-01 Matsushita Electric Industrial Co., Ltd. Système de calibration, appareil cible et méthode de calibration
DE10246067A1 (de) * 2002-10-02 2004-04-22 Robert Bosch Gmbh Verfahren und Vorrichtung zur Kalibrierung eines Bildsensorsystems in einem Kraftfahrzeug

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19536297C2 (de) * 1995-09-29 2003-10-02 Daimler Chrysler Ag Verfahren zur geometrischen Kalibrierung von optischen 3D-Sensoren zur dreidimensionalen Vermessung von Objekten und Vorrichtung hierzu
US5918192A (en) * 1997-01-23 1999-06-29 Intel Corporation Method for calibrating a digital camera to a PC monitor to enhance picture quality of a picture captured by the digital camera and displayed on the PC monitor
DE10115043A1 (de) * 2000-04-25 2002-04-04 Iteris Inc Verfahren und Vorrichtung zur Kalibrierung eines Kamerasystems, insbesondere eines auf einem Fahrzeug angeordneten Kamerasystems

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1120746A2 (fr) * 2000-01-27 2001-08-01 Matsushita Electric Industrial Co., Ltd. Système de calibration, appareil cible et méthode de calibration
DE10246067A1 (de) * 2002-10-02 2004-04-22 Robert Bosch Gmbh Verfahren und Vorrichtung zur Kalibrierung eines Bildsensorsystems in einem Kraftfahrzeug

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2009056050A1 (fr) * 2007-10-24 2009-05-07 Shenzhen Huawei Communication Technologies Co. , Ltd. Procédé et dispositif d'étalonnage de caméra vidéo
US8436904B2 (en) 2007-10-24 2013-05-07 Huawei Device Co., Ltd. Method and apparatus for calibrating video camera
WO2009089932A1 (fr) * 2008-01-15 2009-07-23 Robert Bosch Gmbh Procédé de réglage d'image destiné à une image vidéo
WO2014029720A1 (fr) * 2012-08-20 2014-02-27 Johnson Controls Gmbh Procédé d'étalonnage d'une caméra à temps de vol
CN104504680A (zh) * 2014-11-23 2015-04-08 北京联合大学 一种用于智能车的逆透视标定方法
CN111973134A (zh) * 2020-08-06 2020-11-24 江苏势通生物科技有限公司 基于视觉的测试体对准待测通道的方法、导航方法及系统

Also Published As

Publication number Publication date
DE112005001188A5 (de) 2008-06-19
DE102004033468A1 (de) 2005-12-22

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