CN110246191B - Camera nonparametric model calibration method and calibration precision evaluation method - Google Patents
Camera nonparametric model calibration method and calibration precision evaluation method Download PDFInfo
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Abstract
The invention discloses a camera nonparametric model calibration method and a calibration precision evaluation method, which are carried out by using a camera, a point laser and a turntable, or by using the camera, the point laser, the turntable and a reflector, and comprise the following steps: adjusting the horizontal angle of the camera and/or the laser and/or the reflector, changing the coordinate position of the laser projection point in the image, rotating for m times at a rotation angle delta alpha every time to obtain m groups of coordinate data (u)i,vi) Then, the vertical angle of the camera and/or the laser and/or the reflector is adjusted, the coordinate position of the laser projection point in the image is changed, the laser projection point rotates for n times at a rotation angle delta beta every time, and n groups of coordinate data (u) are obtainedj,vj) (ii) a Fitting (u)i,vi)、(uj,vj) To obtain a straight line l1、l2Establishing an expression of an interpolation function corresponding to the horizontal rotation angle and the vertical rotation angle; to obtain a straight line l1、l2The method is suitable for non-parameter model calibration of the long-focus small-field-of-view camera, and has the advantages of small data acquisition amount and high efficiency.
Description
Technical Field
The invention relates to the technical field of camera calibration, in particular to a camera nonparametric model calibration method and a calibration precision evaluation method.
Background
In a vision measurement system, calibration is an important link, and plays an important role in the stability and the precision level of the whole measurement system. In the calibration process, a common camera model is a pinhole imaging model, an object point and an image point are obtained by perspective projection transformation, and a method for calibrating a camera by applying the imaging model is also called parametric calibration, and the method solves internal parameters of the camera by light beam adjustment and an optimization algorithm, wherein the internal parameters comprise a focal length, a principal point, an external parameter RT matrix and distortion parameters; the parameterized calibration method generally includes calibration methods such as zhang's calibration, self-calibration, active vision, etc., but these calibration methods exist: the parameters are correlated; most optimization algorithms need good initial values, but the initial values are difficult to obtain; every second optimized parameter has a slight difference, and meanwhile, precise targets need to be manufactured for parameter calibration, so that the cost is high.
The other camera calibration method is a nonparametric model calibration method: the corresponding relation between the azimuth angle information of the space incident light and the actual image point can be directly established through the assistance of an external precise angle measuring device, namely a precise rotary table, so that the camera becomes a precise angle measuring device, and the influence of the calibration error of the internal parameters on the measurement precision is eliminated; the common camera nonparametric calibration is that a turntable is used for collecting a series of angle-pixel coordinate point pairs, usually thousands of points are collected to establish an interpolation database, then a new angle value is interpolated according to a two-dimensional interpolation principle, the whole process is relatively complex, the data volume is large, the time consumption is long, for example, a laser collimator, a six-dimensional fine adjustment device, a precise subdivision turntable and a near infrared LED dot matrix are used in a photogrammetry method research based on a nonparametric measurement model published by Tianjin university, Qinghua university Longchang universe and the like, a data table consisting of a large number of angle-image lines is collected, when angles are measured again, a two-dimensional plane interpolation function is used for obtaining angle data, meanwhile, a laser collimator and the precise subdivision turntable are needed to be used for coinciding the intersection points of a camera main point and a laser beam, and the nonparametric calibration method can overcome the defects of the parametric calibration, however, the operation is time-consuming, the coincidence degree cannot be guaranteed, the whole calibration device is complex, and the calibration process is complicated.
Disclosure of Invention
In order to solve the problems, the invention provides a camera nonparametric model calibration method and a calibration precision evaluation method, which are suitable for calibrating a camera nonparametric model with a small field of view and small distortion.
A camera nonparametric model calibration method is characterized in that a camera, a point laser and a turntable are used for calibration, and the camera can acquire laser projection points of the point laser; the turntable is used for changing the coordinate position of the laser projection point in the camera image;
or, calibrating by using a camera, a point laser, a turntable and a reflector, wherein a projection point of the point laser is projected onto the reflector and then reflected into a field of view of the camera by the reflector; the camera is used for collecting images of the laser projection points; the turntable is used for adjusting the coordinate position of the laser projection point reflected by the reflector in the camera image;
the method comprises the following steps:
s1, adjusting the horizontal angle of a camera and/or a laser and/or a reflector, changing the coordinate position of a laser projection point in an image, and rotating an angle delta alpha every time to obtain a group of horizontal rotating angles and image coordinate data; rotating for m times to obtain m groups of one-to-one corresponding horizontal rotation angle and image coordinate data (u)i,vi)，i＝1,2,3……m；
Then, adjusting the vertical angle of the camera and/or the laser and/or the reflector, changing the coordinate position of the laser projection point in the image, and rotating the angle delta beta every time to obtain a group of vertical rotating angles and image coordinate data; rotating for n times to obtain n groups of vertical rotation angle and image coordinate data (u) in one-to-one correspondencej,vj),j＝1,2,3……n；
S2, respectively fitting the image coordinate data (u) by adopting a least square methodi,vi)、(uj,vj) To obtain a straight line l1、 l2Calculating a straight line l1、l2Angle theta to the x-axis of the image coordinate system1、θ2；
Straight line l1、l2Coordinate points (u 'in the constructed coordinate system'i,v'i)、(u'j,v'j) With a point (u) in the image coordinate systemi,vi)、(uj,vj) The relationship between them is as follows:
utilization point (u'i,v'i) U 'of'iCoordinates, and u'iEstablishing an expression of an interpolation function corresponding to the horizontal corner; utilization point (u'j,v'j) V 'of'jCoordinates, and v'jEstablishing an expression of an interpolation function corresponding to the vertical rotation angle;
obtaining a straight line l by using an expression of an interpolation function of a horizontal rotation angle and a vertical rotation angle1、l2And corresponding relation between any coordinate point in the constructed coordinate system and the horizontal corner and the vertical corner.
Further, step S1 is performed as follows:
the camera is fixed on the rotary table, and the rotary table comprises a transverse rotary shaft and a longitudinal rotary shaft and can drive the camera to rotate;
a point laser is fixedly placed in front of the camera, and laser emitted by the point laser is collected by the camera;
marking the initial position of the rotary table, and marking the transverse rotating shaft and the longitudinal rotating shaft at the initial position as an initial transverse rotating shaft and an initial longitudinal rotating shaft; recording a plane where the initial transverse rotating shaft is located and vertical to the initial longitudinal rotating shaft as an initial horizontal plane; recording a plane where the initial longitudinal rotating shaft is located and which is perpendicular to the initial transverse rotating shaft as an initial vertical plane;
s1, keeping an initial horizontal plane unchanged, rotating a rotary table around an initial longitudinal rotating shaft, rotating an angle delta alpha every time, emitting laser by a point laser, collecting a laser point by a camera, and calculating an image coordinate of the circle center of the laser point by a processor to obtain a group of horizontal rotating angles and image coordinate data;
rotating for m times to obtain m groups of one-to-one corresponding horizontal rotation angle and image coordinate data (u)i,vi),i＝1,2,3……m；
Keeping an initial vertical plane unchanged, rotating a turntable around an initial transverse rotating shaft, rotating an angle delta beta every time, emitting laser by a point laser, collecting a laser point by a camera, and calculating an image coordinate of the center of a circle of the laser point by a processor to obtain a group of vertical rotating angles and image coordinate data;
rotating for n times to obtain n groups of vertical rotation angle and image coordinate data (u) in one-to-one correspondencej,vj), j＝1,2,3……n。
Further, step S1 may also be implemented as follows:
the point laser and the camera are fixed on a turntable, the turntable comprises a transverse rotating shaft and a longitudinal rotating shaft, and the camera and the point laser can independently rotate or synchronously rotate;
a plane reflector is fixedly arranged in front of the camera and the point laser and can receive visible laser emitted by the point laser and reflect the laser to the camera;
or:
the method comprises the following steps of fixedly placing a point laser and a camera, placing a plane reflector in front of the camera and the point laser, and installing the plane reflector on a turntable, wherein the plane reflector is used for receiving visible laser emitted by the point laser and reflecting the laser to the camera;
the rotary table comprises a transverse rotating shaft and a longitudinal rotating shaft and can drive the plane reflective mirror to rotate;
marking the initial position of the rotary table, and marking the transverse rotating shaft and the longitudinal rotating shaft at the initial position as an initial transverse rotating shaft and an initial longitudinal rotating shaft; recording a plane where the initial transverse rotating shaft is located and vertical to the initial longitudinal rotating shaft as an initial horizontal plane; recording a plane where the initial longitudinal rotating shaft is located and which is perpendicular to the initial transverse rotating shaft as an initial vertical plane;
s1, keeping an initial horizontal plane unchanged, rotating a rotary table around an initial longitudinal rotating shaft, rotating an angle delta alpha every time, emitting laser to a plane reflector by a point laser, collecting a laser point on the plane reflector by a camera, and calculating an image coordinate of the circle center of the laser point by a processor to obtain a group of horizontal rotating angles and image coordinate data;
rotating for m times to obtain m groups of one-to-one corresponding horizontal rotation angle and image coordinate data (u)i,vi),
i＝1,2,3……m；
Keeping an initial vertical plane unchanged, rotating a rotary table around an initial transverse rotating shaft, emitting laser to a plane reflector by a point laser at a rotation angle delta beta every time, collecting a laser point on the plane reflector by a camera, and calculating an image coordinate of the circle center of the laser point by a processor to obtain a group of vertical rotation angles and image coordinate data;
rotating for n times to obtain n groups of vertical rotation angle and image coordinate data (u) in one-to-one correspondencej,vj), j＝1,2,3……n。
Preferably, in the initial position, the laser emitted by the point laser is perpendicular to the plane mirror, and the laser point formed on the plane mirror is located at the geometric center of the plane mirror.
Preferably, the rotation of the turret about the initial longitudinal axis is: respectively rotating along the clockwise direction and the anticlockwise direction of the initial vertical plane, wherein the rotation angle delta alpha is less than or equal to 0.5 degrees each time;
the rotary table rotates around the initial transverse rotating shaft to: respectively rotate along the clockwise direction and the anticlockwise direction of the initial horizontal plane, and the rotation angle delta beta is less than or equal to 0.5 degree each time.
Further, the interpolation function comprises a cubic spline interpolation function, a piecewise linear interpolation function and a Lagrange interpolation function.
A precision evaluation method for the camera nonparametric model calibration method comprises the following steps:
(1) in the angle range calibrated by the camera, the rotation angle alpha of the turntable around the initial longitudinal rotating shaft is controlled, the rotation angle beta of the turntable around the initial transverse rotating shaft is controlled, the point laser emits laser, the camera acquires the image of the laser point at the moment, and the image coordinate of the circle center of the laser point is recorded as (u)c,vc) Calculating (u)c',vc')
Will uc' substitution of expression v of interpolation function corresponding to horizontal rotation anglecSubstituting the expression of the interpolation function corresponding to the vertical rotation angle to carry out interpolation calculation to obtain a coordinate point(uc',vc') corresponding angles alpha ' and beta ', and then calculating the angle alpha as followsl、βl:
αl＝α'
βl＝arctan(tan(β')cos(α'))
(2) Comparing the rotation angles alpha and beta with the calculated angle alphal、βlAnd evaluating the accuracy of the calculated camera rotation angle.
Or when the rotary table rotates around the initial horizontal rotating shaft by the angle beta1And then rotated by an angle alpha around the initial vertical axis1The method comprises the following steps:
a precision evaluation method for the camera nonparametric model calibration method comprises the following steps:
(1) controlling the rotation angle beta of the turntable around the initial transverse rotating shaft within the angle range calibrated by the camera1And then rotated by an angle alpha around the initial longitudinal axis1The point laser emits laser, the camera collects the laser point image at the moment, and the image coordinate of the circle center of the laser point is recorded as (u)c1,vc1) Calculating (u)c1',vc1')
Will uc1' substitution of expression v of interpolation function corresponding to horizontal rotation anglec1Substituting the expression of the interpolation function corresponding to the vertical rotation angle to perform interpolation calculation to obtain a coordinate point (u)c1',vc1') corresponding angle alpha1'、β1' then, the angle α is obtained by the following calculationl1、βl1:
αl1＝arctan(tan(α1')cos(β1'))
βl1＝β1'
(2) Contrast of rotation angle alpha1、β1And the calculated angle alphal1、βl1And evaluating the accuracy of the calculated camera rotation angle.
The invention is suitable for the non-parametric model calibration of the camera with small field distortion, the invention utilizes the turntable to drive the camera and the laser to rotate, the position of the reflector is kept unchanged, other precision measurement devices are not needed, and the requirement on the calibration device is simple; the measurement data volume is small, and the operation is simple;
because the angle and coordinate mapping relation coordinate system obtained by calibration is not an ideal orthogonal coordinate system, the method can more accurately obtain the relation between the coordinate points and the camera angle by establishing the relation between the image points in the image coordinate system and the coordinate points in the angle and coordinate mapping relation coordinate system.
Drawings
Fig. 1 is a schematic structural diagram of a detection system in embodiment 2.
Detailed Description
The technical solution of the present invention is described in detail below with reference to the accompanying drawings and examples.
Example 1
A camera nonparametric model calibration method is carried out by utilizing a camera, a point laser and a turntable, wherein the camera is fixed on the turntable, and the turntable drives the camera to rotate;
a point laser is fixedly placed in front of the camera, and laser emitted by the point laser is collected by the camera;
marking the initial position of the rotary table, and marking the transverse rotating shaft and the longitudinal rotating shaft at the initial position as an initial transverse rotating shaft and an initial longitudinal rotating shaft; recording a plane where the initial transverse rotating shaft is located and which is perpendicular to the initial longitudinal rotating shaft as an initial horizontal plane; recording a plane where the initial longitudinal rotating shaft is located and which is vertical to the initial transverse rotating shaft as an initial vertical plane;
the method comprises the following steps:
s1, keeping an initial horizontal plane unchanged, rotating a turntable around an initial longitudinal rotating shaft and respectively rotating the turntable along the clockwise direction and the anticlockwise direction of an initial vertical plane, wherein the rotation angle delta alpha is 0.3 degrees each time; the point laser emits laser, the camera collects laser points, and the processor calculates the image coordinates of the circle center of the laser points to obtain a group of horizontal rotation angle and image coordinate data;
rotating for m times to obtain m groups of one-to-one correspondenceHorizontal rotation angle of (d), image coordinate data (u)i,vi),
i is 1,2,3 … … m; the sum of the rotation angles mxDELTA alpha is the working range of the camera in the horizontal direction;
keeping an initial vertical plane unchanged, rotating a turntable around an initial transverse rotating shaft and respectively rotating the turntable along the clockwise direction and the anticlockwise direction of an initial horizontal plane, wherein the angle delta beta of each turn is 0.3 degrees, a point laser emits laser, a camera collects laser points, and a processor calculates the image coordinates of the circle center of the laser point to obtain a group of vertical turn and image coordinate data;
rotating for n times to obtain n groups of vertical rotation angle and image coordinate data (u) in one-to-one correspondencej,vj) J is 1,2,3 … … n, and the sum of the rotation angles n x Δ β is the working range of the camera in the vertical direction;
s2, respectively fitting image coordinate data (u) by adopting a least square methodi,vi)、(uj,vj) To obtain a straight line l1、l2Calculating a straight line l1、l2Angle theta to the x-axis of the image coordinate system1、θ2；
Straight line l1、l2Coordinate points (u 'in the constructed coordinate system'i,v'i)、(u'j,v'j) With a point (u) in the image coordinate systemi,vi)、(uj,vj) The relationship between them is as follows:
utilization point (u'i,v'i) U 'of'iCoordinates, and u'iEstablishing an expression of a cubic spline interpolation function corresponding to the horizontal corner; utilization point (u'j,v'j) V 'of'jCoordinates, and v'jThe coordinates correspond toEstablishing an expression of an interpolation function corresponding to the vertical corner; to obtain a straight line l1、l2And corresponding relation between any coordinate point in the constructed coordinate system and the horizontal corner and the vertical corner.
And then, carrying out precision evaluation on the camera nonparametric model calibration method by utilizing the following steps:
(1) in the angle range calibrated by the camera, the rotation angle alpha of the turntable around the initial longitudinal rotating shaft is controlled, the rotation angle beta of the turntable around the initial transverse rotating shaft is controlled, the point laser emits laser, the camera acquires the image of the laser point at the moment, and the image coordinate of the circle center of the laser point is recorded as (u)c,vc) Calculating (u)c',vc')
Will uc' substitution of expression v of interpolation function corresponding to horizontal rotation anglecSubstituting the expression of the interpolation function corresponding to the vertical rotation angle to carry out interpolation calculation to obtain a coordinate point (u)c',vc') corresponding angles alpha ' and beta ', and then calculating the angle alpha as followsl、βl:
αl＝α'
βl＝arctan(tan(β')cos(α'))
(2) Comparing the rotation angles alpha and beta with the calculated angle alphal、βlAnd evaluating the accuracy of the calculated camera rotation angle.
Example 2
As shown in fig. 1, in this embodiment, another method is adopted to change the coordinate position of a laser projection point in an image, and a camera nonparametric model calibration method is performed by using a camera 1, a point laser 2, a turntable 3 and a reflector 4, the point laser and the camera are both fixed on the turntable 3, the turntable 3 comprises a transverse rotating shaft and a longitudinal rotating shaft, and the camera and the point laser are driven to synchronously rotate, or the turntable only drives the camera to rotate, the position of the point laser is unchanged, or the turntable only drives the point laser to rotate, and the position of the camera is unchanged;
a plane reflector 4 is fixedly arranged in front of the camera and the point laser, and can receive visible laser emitted by the point laser and reflect the laser to the camera; in the initial position, the laser emitted by the point laser is perpendicular to the plane reflector, and the laser point formed on the plane reflector is positioned at the geometric center of the plane reflector.
Marking the initial position of the rotary table, and marking the transverse rotating shaft and the longitudinal rotating shaft at the initial position as an initial transverse rotating shaft and an initial longitudinal rotating shaft; recording a plane where the initial transverse rotating shaft is located and which is perpendicular to the initial longitudinal rotating shaft as an initial horizontal plane; recording a plane where the initial longitudinal rotating shaft is located and which is vertical to the initial transverse rotating shaft as an initial vertical plane;
the method comprises the following steps:
s1, keeping an initial horizontal plane unchanged, rotating a rotary table around an initial longitudinal rotating shaft, rotating an angle delta alpha every time, emitting laser to a plane reflector by a point laser, collecting a laser point on the plane reflector by a camera, and calculating an image coordinate of the circle center of the laser point by a processor to obtain a group of horizontal rotating angles and image coordinate data;
rotating for m times to obtain m groups of one-to-one corresponding horizontal rotation angle and image coordinate data (u)i,vi),
i＝1,2,3……m；
Keeping an initial vertical plane unchanged, rotating a rotary table around an initial transverse rotating shaft, emitting laser to a plane reflector by a point laser at a rotation angle delta beta every time, collecting a laser point on the plane reflector by a camera, and calculating an image coordinate of the circle center of the laser point by a processor to obtain a group of vertical rotation angles and image coordinate data;
rotating for n times to obtain n groups of vertical rotation angle and image coordinate data (u) in one-to-one correspondencej,vj), j＝1,2,3……n。
S2, respectively fitting image coordinate data (u) by adopting a least square methodi,vi)、(uj,vj) To obtain a straight line l1、l2Calculating a straight line l1、l2Angle theta to the x-axis of the image coordinate system1、θ2；
Straight line l1、l2Coordinate points (u 'in the constructed coordinate system'i,v'i)、(u'j,v'j) With a point (u) in the image coordinate systemi,vi)、(uj,vj) The relationship between them is as follows:
utilization point (u'i,v'i) U 'of'iCoordinates, and u'iEstablishing an expression of a cubic spline interpolation function corresponding to the horizontal corner; utilization point (u'j,v'j) V 'of'jCoordinates, and v'jEstablishing an expression of an interpolation function corresponding to the vertical corner; to obtain a straight line l1、l2And corresponding relation between any coordinate point in the constructed coordinate system and the horizontal corner and the vertical corner.
And then, carrying out precision evaluation on the camera nonparametric model calibration method by utilizing the following steps:
(1) controlling the rotation angle beta of the turntable around the initial transverse rotating shaft within the angle range calibrated by the camera1And then rotated by an angle alpha around the initial longitudinal axis1The point laser emits laser, the camera collects the laser point image at the moment, and the image coordinate of the circle center of the laser point is recorded as (u)c1,vc1) Calculating (u)c1',vc1')
Will uc1' substitution of expression v of interpolation function corresponding to horizontal rotation anglec1' substitution into interpolation function corresponding to vertical rotation angleThe expression of the number, and the interpolation calculation is carried out to obtain a coordinate point (u)c1',vc1') corresponding angle alpha1'、β1' then, the angle α is obtained by the following calculationl1、βl1:
αl1＝arctan(tan(α1')cos(β1'))
βl1＝β1'
(2) Contrast of rotation angle alpha1、β1And the calculated angle alphal1、βl1And evaluating the accuracy of the calculated camera rotation angle.
Example 3
Compared with the embodiment 2, the embodiment adopts another mode, the coordinate position of the laser projection point in the image is changed, the camera nonparametric model calibration method is carried out by utilizing the camera, the point laser, the rotary table and the reflector, the point laser and the camera are fixedly placed, the plane reflector is placed in front of the camera and the point laser and is arranged on the rotary table, and the plane reflector is used for receiving the visible laser emitted by the point laser and reflecting the laser to the camera;
keeping the initial horizontal plane unchanged, the turntable drives the plane reflector to rotate around the initial longitudinal rotating shaft, the angle delta alpha is rotated each time, the point laser emits laser to the plane reflector, the camera collects the laser point on the plane reflector, and the laser point is rotated m times to obtain m groups of one-to-one corresponding horizontal rotating angle and image coordinate data (u and u are respectively obtainedi,vi),
Keeping the initial vertical plane unchanged, driving the plane reflector to rotate around the initial transverse rotating shaft by the turntable at an angle delta beta each time, emitting laser to the plane reflector by the point laser, collecting laser points on the plane reflector by the camera, and rotating for n times to obtain n groups of vertical rotating angles and image coordinate data (u) in one-to-one correspondencej,vj)；
S2, respectively fitting image coordinate data (u) by adopting a least square methodi,vi)、(uj,vj) To obtain a straight line l1、l2Calculating a straight line l1、l2From the x-axis of the image coordinate systemIncluded angle theta1、θ2；
Straight line l1、l2Coordinate points (u 'in the constructed coordinate system'i,v'i)、(u'j,v'j) With a point (u) in the image coordinate systemi,vi)、(uj,vj) The relationship between them is as follows:
utilization point (u'i,v'i) U 'of'iCoordinates, and u'iEstablishing an expression of a cubic spline interpolation function corresponding to the horizontal corner; utilization point (u'j,v'j) V 'of'jCoordinates, and v'jEstablishing an expression of an interpolation function corresponding to the vertical corner; to obtain a straight line l1、l2And corresponding relation between any coordinate point in the constructed coordinate system and the horizontal corner and the vertical corner.
For convenience in explanation and accurate definition in the appended claims, the terms "upper", "lower", "left" and "right" are used to describe exemplary embodiments of feature locations.
Claims (9)
1. A camera nonparametric model calibration method is characterized in that a camera, a point laser and a turntable are used for calibration, and the camera can acquire laser projection points of the point laser; the turntable is used for changing the coordinate position of the laser projection point in the camera image;
or, calibrating by using a camera, a point laser, a turntable and a reflector, wherein a projection point of the point laser is projected onto the reflector and then reflected into a field of view of the camera by the reflector; the camera is used for acquiring an image of the laser projection point; the turntable is used for adjusting the coordinate position of the laser projection point reflected by the reflector in the camera image;
the method is characterized by comprising the following steps:
s1, adjusting the horizontal angle of a camera and/or a laser and/or a reflector, changing the coordinate position of a laser projection point in an image, and rotating an angle delta alpha every time to obtain a group of horizontal rotating angles and image coordinate data; rotating for m times to obtain m groups of one-to-one corresponding horizontal rotation angle and image coordinate data (u)i,vi)，i＝1,2,3……m；
Then, adjusting the vertical angle of the camera and/or the laser and/or the reflector, changing the coordinate position of the laser projection point in the image, and rotating the angle delta beta every time to obtain a group of vertical rotating angles and image coordinate data; rotating for n times to obtain n groups of vertical rotation angle and image coordinate data (u) in one-to-one correspondencej,vj),j＝1,2,3……n；
S2, respectively fitting the image coordinate data (u) by adopting a least square methodi,vi)、(uj,vj) To obtain a straight line l1、l2Calculating a straight line l1、l2Angle theta to the x-axis of the image coordinate system1、θ2；
Straight line l1、l2Coordinate points (u 'in the constructed coordinate system'i,v'i)、(u'j,v'j) With a point (u) in the image coordinate systemi,vi)、(uj,vj) The relationship between them is as follows:
utilization point (u'i,v'i) U 'of'iCoordinates, and u'iEstablishing an expression of an interpolation function corresponding to the horizontal rotation angle; utilization point (u'j,v'j) V 'of'jCoordinates, and v'jEstablishing an expression of an interpolation function corresponding to the vertical corner;
obtaining a straight line l by using an expression of an interpolation function of a horizontal rotation angle and a vertical rotation angle1、l2And corresponding relation between any coordinate point in the constructed coordinate system and the horizontal corner and the vertical corner.
2. The calibration method of the nonparametric model of the camera as claimed in claim 1, wherein the step S1 adopts the following method:
the camera is fixed on a rotary table, and the rotary table comprises a transverse rotating shaft and a longitudinal rotating shaft and can drive the camera to rotate;
a point laser is fixedly placed in front of the camera, and laser emitted by the point laser is collected by the camera;
marking the initial position of the rotary table, and marking the transverse rotating shaft and the longitudinal rotating shaft at the initial position as an initial transverse rotating shaft and an initial longitudinal rotating shaft; recording a plane where the initial transverse rotating shaft is located and which is vertical to the initial longitudinal rotating shaft as an initial horizontal plane; recording a plane where the initial longitudinal rotating shaft is located and which is perpendicular to the initial transverse rotating shaft as an initial vertical plane;
s1, keeping an initial horizontal plane unchanged, rotating a turntable around an initial longitudinal rotating shaft, rotating an angle delta alpha every time, emitting laser by a point laser, collecting a laser spot by a camera, and calculating an image coordinate of the circle center of the laser spot by a processor to obtain a group of horizontal rotating angles and image coordinate data;
rotating for m times to obtain m groups of one-to-one corresponding horizontal rotation angle and image coordinate data (u)i,vi),i＝1,2,3……m；
Keeping an initial vertical plane unchanged, rotating a turntable around an initial transverse rotating shaft, rotating an angle delta beta every time, emitting laser by a point laser, collecting a laser point by a camera, and calculating an image coordinate of the center of a circle of the laser point by a processor to obtain a group of vertical rotating angles and image coordinate data;
rotating for n times to obtain n groups of vertical rotation angle and image coordinate data (u) in one-to-one correspondencej,vj),j＝1,2,3……n。
3. The calibration method of the nonparametric model of the camera as claimed in claim 1, wherein the step S1 adopts the following method:
the point laser and the camera are fixed on a turntable, the turntable comprises a transverse rotating shaft and a longitudinal rotating shaft, and the camera and the point laser can independently rotate or synchronously rotate;
a plane reflector is fixedly arranged in front of the camera and the point laser and can receive visible laser emitted by the point laser and reflect the laser to the camera;
or:
the method comprises the following steps of fixedly placing a point laser and a camera, placing a plane reflector in front of the camera and the point laser, and installing the plane reflector on a turntable, wherein the plane reflector is used for receiving visible laser emitted by the point laser and reflecting the laser to the camera;
the rotary table comprises a transverse rotating shaft and a longitudinal rotating shaft and can drive the plane reflective mirror to rotate;
marking the initial position of the rotary table, and marking the transverse rotating shaft and the longitudinal rotating shaft at the initial position as an initial transverse rotating shaft and an initial longitudinal rotating shaft; recording a plane where the initial transverse rotating shaft is located and which is vertical to the initial longitudinal rotating shaft as an initial horizontal plane; recording a plane where the initial longitudinal rotating shaft is located and which is perpendicular to the initial transverse rotating shaft as an initial vertical plane;
s1, keeping an initial horizontal plane unchanged, rotating a rotary table around an initial longitudinal rotating shaft, rotating an angle delta alpha every time, emitting laser to a plane reflector by a point laser, collecting a laser point on the plane reflector by a camera, and calculating an image coordinate of the circle center of the laser point by a processor to obtain a group of horizontal rotating angles and image coordinate data;
rotating for m times to obtain m groups of one-to-one corresponding horizontal rotation angle and image coordinate data (u)i,vi),
i＝1,2,3……m；
Keeping an initial vertical plane unchanged, rotating a rotary table around an initial transverse rotating shaft, and rotating an angle delta beta every time, wherein a point laser emits laser to a plane reflector, a camera collects a laser point on the plane reflector, and a processor calculates an image coordinate of the circle center of the laser point to obtain a group of vertical rotation angles and image coordinate data;
rotating for n times to obtain n groups of vertical rotation angle and image coordinate data (u) in one-to-one correspondencej,vj),j＝1,2,3……n。
4. The calibration method for the nonparametric model of the camera as defined in claim 3, wherein in the initial position, the laser emitted by the point laser is perpendicular to the plane mirror, and the laser point formed on the plane mirror is located at the geometric center of the plane mirror.
5. The method for calibrating a non-parametric model of a camera as claimed in claim 2, wherein the rotation of the turntable about the initial longitudinal axis is: respectively rotating along the clockwise direction and the anticlockwise direction of the initial vertical plane, wherein the rotation angle delta alpha is less than or equal to 0.5 degrees each time;
the rotary table rotates around the initial transverse rotating shaft to: the rotation is respectively along the clockwise direction and the anticlockwise direction of the initial horizontal plane, and the rotation angle delta beta is less than or equal to 0.5 degrees every time.
6. A method for calibrating a non-parametric model of a camera as defined in claim 3, wherein the rotation of the turntable about the initial longitudinal axis is: respectively rotating along the clockwise direction and the anticlockwise direction of the initial vertical plane, wherein the rotation angle delta alpha is less than or equal to 0.5 degrees each time;
the rotary table rotates around the initial transverse rotating shaft to: the rotation is respectively along the clockwise direction and the anticlockwise direction of the initial horizontal plane, and the rotation angle delta beta is less than or equal to 0.5 degrees every time.
7. The method for calibrating a nonparametric model of a camera as claimed in claim 1, characterized in that said interpolation function comprises a cubic spline interpolation function, a piecewise linear interpolation function, a lagrange interpolation function.
8. A precision evaluation method for the camera nonparametric model calibration method according to any one of claims 1 to 7 is characterized by comprising the following steps:
(1) in the angle range calibrated by the camera, the rotation angle alpha of the turntable around the initial longitudinal rotating shaft is controlled, the rotation angle beta of the turntable around the initial transverse rotating shaft is controlled, the point laser emits laser, the camera acquires the image of the laser point at the moment, and the image coordinate of the circle center of the laser point is recorded as (u)c,vc) Calculating (u)c',vc')
Will uc' substitution of expression v of interpolation function corresponding to horizontal rotation anglecSubstituting the expression of the interpolation function corresponding to the vertical rotation angle to carry out interpolation calculation to obtain a coordinate point (u)c',vc') corresponding angles alpha ' and beta ', and then calculating the angle alpha as followsl、βl:
αl＝α'
βl＝arctan(tan(β')cos(α'))
(2) Comparing the rotation angles alpha and beta with the calculated angle alphal、βlAnd evaluating the accuracy of the calculated camera rotation angle.
9. A precision evaluation method for the camera nonparametric model calibration method according to any one of claims 1 to 7 is characterized by comprising the following steps:
(1) controlling the rotation angle beta of the turntable around the initial transverse rotating shaft within the angle range calibrated by the camera1And then rotated by an angle alpha around the initial longitudinal axis1The point laser emits laser, the camera collects the laser point image at the moment, and the image coordinate of the circle center of the laser point is recorded as (u)c1,vc1) Calculating (u)c1',vc1')
Will uc1' substitution of expression v of interpolation function corresponding to horizontal rotation anglec1Substituting the expression of the interpolation function corresponding to the vertical rotation angle to carry out interpolation calculation to obtain a coordinate point (u)c1',vc1') corresponding angle alpha1'、β1' the angle α is obtained by the following calculationl1、βl1:
αl1＝arctan(tan(α1')cos(β1'))
βl1＝β1'
(2) Contrast of rotation angle alpha1、β1And the calculated angle alphal1、βl1And evaluating the accuracy of the calculated camera rotation angle.
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