JP2010287074A - Camera calibration device, camera calibration method, camera calibration program and recording medium recording the program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce imaging work cost, and to perform camera calibration with high accuracy even when a camera and a reference object are apart from each other with simple work. <P>SOLUTION: The camera calibration device 1 calibrates internal parameters of an imaging device 5 and external parameters including an attitude and a position, and from an image acquired from the imaging device 5. The camera calibration device includes: a reference point detection means 4 detecting image coordinates of aligned reference points of the reference object 3 from the image; a reference object control means 6 reversely rotating the image around the origin of the image coordinates according to an optical axis rotation angle, and moving the position of the reference object 3; a geometric measurement means 7 measuring a distance L and an elevation angle Ψ between the imaging device 5 and a measurement device 10 by the measurement device 10; and a camera calibration means 8 calibrating the external parameters and the internal parameters of the imaging device 5 from the optical axis rotation angle Ψ, the distance L and the elevation angle between the imaging device 5 and the measurement device 10, and the image coordinates of the reference points detected after reference object control by use of relation of projective geometry between the imaging device 5 and the reference points A, B, O. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a camera calibration apparatus that can be used for calibration (determining camera parameters) of a security camera or a fixed camera installed for crime prevention purposes and suppresses the cost of camera calibration work.

  Camera calibration (camera calibration) is performed to obtain internal parameters such as a camera-specific focal length and image center, and external parameters such as posture and position information at the time of camera placement. As shown in FIG. 19, in the conventional method, a two-dimensional object in which a lattice pattern is drawn is photographed by a camera to be calibrated, and a camera is obtained from geometric information about the reference object and projection information on an image observed by the camera. Internal and external parameters (both are collectively referred to as camera parameters) are estimated (Non-Patent Document 1).

  Furthermore, as an example using a simpler reference object, as shown in FIG. 20, a method is also disclosed in which a one-dimensional object with a known length is used to shoot with the reference point A fixed and calibrate the camera from the image. (Non-Patent Document 2).

  In computer vision, there is a basic principle called Structure From Motion, and there is a method for restoring the three-dimensional shape and movement of a subject by moving the camera relative to a stationary subject (for moving subjects). On the other hand, the principle is the same even if the camera is stationary). Self-calibration (also called auto-calibration) is one of the methods based on this principle. It does not require the above-mentioned known reference object and uses a feature point observed from a static video scene. Estimate the parameters.

Z. Zhang, “A flexible new technology for camera calibration”, IEEE Trans. on Pattern Analysis and Machine Intelligence, Vol. 22, no. 11, pp. 1330-1334, 2000. Z. Zhang, “Camera calibration with one-dimensional objects”, IEEE Trans. on Pattern Analysis and Machine Intelligence, Vol. 26, no. 7, pp. 892-699, 2004.

  In conventional camera calibration methods, it is common practice to use a reference object, as represented by Non-Patent Documents 1 and 2. In FIG. 19, the two-dimensional coordinates of the reference point on the two-dimensional object are known (Non-Patent Document 1). In FIG. 20, the length L of the one-dimensional object, the distance from point A to point C, and the point B to point C It is a premise that the ratio of the distance to is known (Non-Patent Document 2).

  In the case of camera calibration using such a reference object, it is necessary to photograph a sufficient amount of reference points. In order to respond to this, a lot of time is taken for the work of photographing the reference object before the camera calibration. In a fixed-point camera such as a security camera, it is not always guaranteed to capture a sufficient amount of reference points for camera calibration, and there is not always enough time to capture them. Depending on the operational situation, camera calibration must be accepted from a small number of reference points.

  In the camera calibration in Non-Patent Document 1, a reference object (a two-dimensional plane pattern or the like) is used. However, if the distance from the camera is increased, the reference object appears smaller, so that the camera calibration is sufficiently accurate. I can't. In order to solve this, it is conceivable to prepare a two-dimensional plane pattern having a sufficiently large size even when taken from a distance, but it is not realistic to prepare a huge plane pattern.

  On the other hand, according to the self-calibration, the camera can be calibrated based on the feature points observed from the static video scene without requiring a known reference object. However, even in the camera calibration method, it is necessary to measure a sufficient amount of image coordinates of feature points from a time-series image. If a certain amount of error is mixed in the measurement of image coordinates of the feature points, the calibration accuracy is greatly deteriorated. The problem is pointed out.

  The present invention has been made in order to solve the above-described problems of the prior art, and reduces the photographing cost. Even when the camera and the reference object are separated from each other, the camera calibration can be performed with high accuracy with a simple operation. It is a solution issue to do.

  One aspect of the present invention is a camera calibration device that calibrates internal parameters of an imaging device and external parameters including posture and position from an image acquired from a single eye or a plurality of imaging devices, the shape of which is known from the image Reference point detecting means for detecting image coordinates of reference points arranged in a straight line in the reference object, and calculating an optical axis rotation angle between a line segment formed from the reference points and a reference axis on the image coordinates, A reference object that reversely rotates the image around the origin of the image coordinates according to the calculated optical axis rotation angle, and moves the position of the reference object so that one of the reference points coincides with the origin of the image coordinates The imaging means using a control means, a geometric measurement means for measuring an elevation angle and a distance between the imaging device and the measuring device by a measuring device provided on the reference object, and a projective geometry relationship between the reference point and the imaging device. Equipment and instrumentation Comprises elevation angle and the distance between the optical axis rotation angles, and the image coordinates of the reference points detected after a reference object control, and camera calibration means for calibrating the internal parameters and external parameters of the imaging apparatus.

  Another aspect of the present invention is a camera calibration method for calibrating external parameters including an internal parameter, an orientation, and a position of an imaging device from an image acquired using a single eye or a plurality of imaging devices. A reference point detecting step in which the output means detects image coordinates of reference points arranged in a straight line in a reference object having a known shape from the image; and a line segment and image coordinates formed from the reference point by the reference object control means The optical axis rotation angle between the upper reference axis is calculated, the image is rotated backward about the origin of the image coordinates according to the calculated optical axis rotation angle, and one of the reference points is the image coordinate. A reference object control step for moving the position of the reference object so as to coincide with the origin of the reference object, and a geometric measurement unit in which the geometric measurement means measures the elevation angle and distance between the imaging device and the measurement device by the measurement device provided on the reference object. And the camera calibration means detect the elevation angle and distance between the imaging device and the measuring device, the optical axis rotation angle, and the reference object control using the relationship of the projective geometry between the reference point and the imaging device. A camera calibration step of calibrating internal parameters and external parameters of the imaging device from the image coordinates of the reference point.

  In addition, this invention can be comprised as a program for functioning a computer as each means to calibrate the said camera calibration apparatus. This program can also be provided in a form stored in a recording medium.

  According to the present invention, it is possible to reduce the photographing work cost and perform camera calibration with high accuracy with a simple work even when the camera and the reference object are separated from each other.

It shows the camera and the reference point arrangement relationship (Y _w Z _w plane). It shows the camera and the reference point arrangement relationship (X _w Y _w plane). It shows the camera and the reference point arrangement relationship when the point A is projected on the image center (Y _w Z _W surface). It shows the camera and the reference point arrangement relationship when the point A is projected to the image center (X _w Y _w). Explanatory drawing of the image sample in which the point A was projected on the image center. 1 is a basic configuration diagram of a camera calibration device of the present invention. 3 is a flowchart showing the overall processing of the camera calibration device of the present invention. An overview of a reference object taken with a camera. The sample image when the reference object of FIG. 8 or FIG. 11 is imaged. The flowchart which shows the process of a reference object control part. Overview of reference object with background. The image which carried out rotation correction of the sample image of FIG. The flowchart which shows the detailed process of S25 (translational movement of a reference object) of FIG. An image in which the position of the reference object is controlled so that the point A is the image center. Explanatory drawing of the translation control of the reference object of FIG. 8 or FIG. The flowchart which shows the process of a geometric measurement control part and a camera calibration process part. The figure which shows the positional relationship of a measurement point and a reference point. 9 is a flowchart showing processing of a geometric measurement control unit and a camera calibration processing unit in the second embodiment. Explanatory drawing which shows the conventional camera calibration operation | work using a two-dimensional planar object as a reference object. Explanatory drawing which shows the conventional camera calibration operation | work which used the one-dimensional object as a reference object.

Hereinafter, a camera calibration apparatus according to an embodiment of the present invention will be described. The projective geometry relationship between the three points on the straight line and the camera, which is the basic principle of this camera calibration device, will be described. First, in order to describe the projection relationship between the camera viewpoint and the three-dimensional point, a reference coordinate system is set. Although this coordinate system may be set arbitrarily, for convenience of explanation, as shown in FIGS. 1 and 2, a certain point on the ground or floor (or a point on an arbitrary plane) may be used. Assumes world coordinate system as origin. A three-dimensional point (reference point) in the space is expressed as coordinates in this world coordinate system, and the reference points to be observed for camera calibration are O = (0,0,0) and A = (0,0, h _1). ), B = (0, 0, h ₂ ).

Assume that the geometric projection by a camera can be modeled as a perspective projection according to a pinhole camera. If a three-dimensional point expressed in the world coordinate system is P _j = (X _j , Y _j , Z _j ) and the camera viewpoint position is (Tx, Ty, Tz), the point P _j is observed on the image. Two-dimensional coordinate values (image coordinates) p _j = (x _j , y _j ) are given by the following equations (1) and (2).

Here, f is a focal length in units of pixels, and R ₁₁ , R ₁₂ ,..., R ₃₃ correspond to elements of a 3 × 3 rotation matrix. Reference point A, B, because O is a point on the Z _w axis, rotation about the Y-axis of the camera may be set arbitrarily, providing each rotating element and the following (3) to (11) below.

  Φ and θ in the above equations (3) to (11) indicate rotation angles (tilt angle, optical axis rotation angle) around the X axis and Z axis in the camera coordinate system XYZ in FIGS.

The image coordinates observed on the image of the reference point O = (0, 0, 0), A = (0, 0, h ₁ ), B = (0, 0, h ₂ ) are respectively represented by p ₀ = (x ₀ , Y ₀ ), p ₁ = (x ₁ , y ₁ ), and p ₂ = (x ₂ , y ₂ ), the following equations (12) and (13) can be derived. However, the following formulas (14) and (15) are substituted.

  Therefore, the following equation (16) is obtained from the above equations (12) and (13).

The above equation (16) is a rotation around the camera Z axis if the image coordinates p ₁ , p ₂ , p _{0 of the} three reference points and the heights h ₁ , h ₂ on the Z axis of the reference points A, B are given. The angle θ (hereinafter referred to as the optical axis rotation angle) θ is obtained. Furthermore, since the relationship between the focal length f and the rotation angle (hereinafter referred to as the tilt angle) φ around the camera X axis is the above equation (13), if the tilt angle φ is obtained by some means, the above equation (13) The focal length f can be obtained using the relationship. Alternatively, if the focal length f is obtained by some means, the tilt angle φ can be obtained using the relationship of the above equation (13).

  The camera calibration device obtains the tilt angle φ around the camera X axis by some measuring device, and calculates the focal length f using the relationship of the above equation (13). However, in order to measure the tilt angle φ of the camera by laser measurement, it is necessary to have a special arrangement with the camera viewpoint position (Tx, Ty, Tz) and the measurement point of the measuring device. This will be described with reference to FIGS.

In FIG. 3, the measurement point of the measurement device is assumed to be the position of the reference point A. If the distance L to the object (the distance from A to the viewpoint in FIG. 3) and the tilt angle (elevation angle) Ψ are obtained by this distance measuring apparatus, the depth d ( = Lcos (Ψ)), and the height h (= Lsin (Ψ)) with respect to the reference point is obtained. However, by the measuring device, that these values can be measured is located on the measurement point and the camera viewpoint position (Tx, Ty, Tz) is Y _w axis of the measuring apparatus as shown in FIG. 4, illustration on the image As shown in FIG. 5, the image coordinate p ₁ of the reference point A is located at the center of the image, and the other reference points B and O are projected on the y-axis (vertical center axis) on the image coordinate. Is a condition. That is, it is necessary to change the positions of the reference points A, B, and O by another means so that the reference point A and the other reference points B and O can be observed in the state shown in FIG.

If the viewpoint position (Tx, Ty, Tz) of the camera and the measurement points of the measurement device are specially arranged as shown in FIGS. 3 to 5, the height h, the depth d, and the inclination angle φ are utilized using the measurement device. Therefore, the viewpoint position (Tx, Ty, Tz) is obtained as (0, d, h + h ₁ ) on the world coordinate system with the reference point O as the origin. Further, the inclination angle (elevation angle) [psi is seen in FIG. 3, the inclination angle of the camera φ (= Ψ-π / 2 ) is obtained the (phi is vertically downward direction (the direction of -Z _w axis) phi = 0, Y _w axis and a φ = -π / 2 when facing in the opposite direction, the inclination angle of the camera is the angle of rotation which is defined within this range (-π / 2 <φ <0 )). Since the tilt angle φ can be calculated with this, the focal length f is obtained using the relationship of the above equation (13). The above is the basic principle.

[Embodiment 1]
FIG. 6 shows a configuration example of the camera calibration apparatus 1 according to the first embodiment of the present invention. The camera calibration apparatus 1 according to the first embodiment includes an image input unit 2 that acquires an image used for camera calibration, a reference point detection unit 4 that detects a reference point of a reference object 3 from an image acquired by the image input unit 2, and A reference object control unit 6 for controlling the position of the reference object 3 by calculating the rotation angle of the image by calculating the optical axis rotation angle of the image pickup apparatus (hereinafter referred to as a camera) 5 using the reference point, and the control thereof. A geometric measurement control unit 7 that measures an elevation angle (hereinafter referred to as an inclination angle) and a distance between the camera 5 and the measurement device while controlling the orientation of the measurement device provided on the reference object 3 toward the camera 5; A camera calibration processing unit 8 that calibrates camera parameters using the geometric relationship between the geometric information obtained by the geometric measurement control unit 7 and the image coordinates of the reference point.

  Here, a mode in which the camera 5 to be calibrated is connected to the camera calibration apparatus 1 is shown, but the camera 5 to be calibrated does not necessarily have to be connected to the camera calibration apparatus 1 as a component, and a sample image necessary for calibration May be acquired via the image input unit 2. The image input unit 2 may be in a form using a recording medium such as a hard disk, a RAID device, a CD-ROM, or a form using remote data resources via a network. Furthermore, a method for acquiring an image in real time according to the necessity of processing is possible, and the present invention does not necessarily require a storage device. Further, the camera calibration device 1 has an image input unit 2, a reference point detection unit 4, and a reference object control as a result of cooperation between computer hardware resources (CPU, memory, hard disk drive device, communication interface, etc.) and software. Functions as a unit 6, a geometric measurement control unit 7, and a camera calibration processing unit 8.

FIGS. 8A and 8B are external views of the reference object 3 presented to the calibration target camera 5. As shown in FIG. 8A, A, B, and O are markers (reference points) that can be observed by the camera 5 and are arranged on one straight line (vertical bar 9). The marker (reference point) O is the origin of the world coordinate system, and the height from the marker O to the markers A and B is h ₁ and h ₂ , respectively. Further, a laser distance measuring unit 10 is provided as a measuring device at the top of the reference object 3.

  In the first embodiment, if the distance between the camera 5 and the reference object 3 is sufficiently large, the measurement point in the laser distance measurement unit 10 is assumed to be approximately the same position as the reference point A. The laser distance measuring unit 10 can freely control the posture according to the camera 5 to be calibrated, as shown in FIG. 8B.

  Hereinafter, the processing steps of the camera calibration apparatus 1 will be described with reference to the flowchart of FIG.

  S11: In the reference object control unit 6 shown in FIG. 6, the reference object 3 designed as shown in FIG. 8 is installed in front of the camera 5 as a photographing subject for camera calibration. In this initial state, the camera 5 is not ready to be calibrated.

  Here, a sample image obtained by photographing the reference object 3 with the camera 5 is acquired via the image input unit 2. FIG. 9 shows an example of the sample image. In FIG. 9, the x-axis is set in the horizontal direction of the image plane, the y-axis is set in the vertical direction, and the image center is set as the center of the xy image coordinate system.

  Next, a pretreatment for camera calibration in FIG. 10 is performed on the sample image in the reference object control unit 6. Here, since the reference points A, B, and O are arranged along the vertical bar 9, the linear parameters of the reference bar (vertical bar 9) are detected by voting processing by Hough transformation on the sample image (S21). (S22).

S12: If the straight line parameter can be detected in S11, a reference point is detected. That is, the reference point detection unit 4 scans along the straight line, and detects the image coordinates of the reference points A, B, and O. If the reference points A, B, and O are painted with a color that is conspicuous even with the camera 5, the reference points A, B, and O can be easily detected by scanning on the vertical bar 9. Alternatively, as shown in FIG. 11, if the special background 12 is painted so that the reference points A, B, and O can be easily detected, the positions of the reference points A, B, and O can be easily detected in the same manner. Can do. In this way, in the reference point detection unit 4, the image coordinates corresponding to the reference points A, B, and O are set to p ₁ = (x ₁ , y ₁ ), p ₂ = (x ₂ , y ₂ ), and p _{0, respectively.} = (X ₀ , y ₀ )

S13: Returning to the flowchart shown in FIG. 10, the reference object control unit 6 executes the calculation and rotation correction of the optical axis rotation angle θ, that is, S23 and S24 in the processing process of FIG. Here, from the extracted image coordinates P ₁ , P ₂ , P _{0 of} the reference points A, B, O and the known h ₁ , h ₂ , the reference object control unit 6 uses the above-mentioned equations (14) and (15). Α and β are calculated according to the equation, and the optical axis rotation angle of the image (the line formed from the reference points A, B, and O and the y axis (reference axis) on the image coordinates) is calculated using the equation (16). The optical axis rotation angle between them is calculated (S23). Then, the reference object control unit 6 performs reverse rotation of the optical axis rotation angle θ about the image origin to obtain the image shown in FIG. 12 (S24).

S14: The translation control of the reference object 3 is performed by the reference object control unit 6, and the position of the reference object 3 is changed according to the processing flowchart of FIG. In this control, the position of the reference object 3 is changed until the image shown in FIG. 14 is obtained, that is, until the image coordinates P ₁ = (X ₁ , y ₁ ) of the reference point A coincides with the image origin (FIG. 10). S25). The position change of the reference object 3 will be described based on the flowchart of FIG.

As shown in FIG. 15, the reference object 3 is moved by ΔX along the _Xw axis set on the base 11 according to the command (S31). Since the image coordinates P ₁ , P ₂ , and P _{0 of the} reference points A, B, and O are sequentially obtained from the reference point detection unit 4, it is determined whether or not the image coordinates p ₁ of the reference point A matches the image center ( S35). If it is determined that a matching point is not found even when moving within the range that can move in the _Xw axis direction (S32), the reference object 3 is moved by ΔY along the _Yw axis direction (S33). The position of the reference object 3 in the _Xw- axis direction is restored (S34), and the reference object 3 is moved again by ΔX along the _Xw- axis direction (S31). In this manner, the reference object 3 is moved on the X _w Y _w plane until it is determined that the image coordinate p ₁ of the point A overlaps the image center (S35). When the control by the reference object control unit 6 is completed, the one-dimensional object composed of the reference points A, B, and O coincides with the y axis on the screen.

In a state where the processing in the reference object control unit 6 is completed, the reference point detection unit 4 measures the image coordinates P ₁ , P ₂ , P ₀ of the reference points A, B, O again. As shown in FIG. 14, since the vertical bar 9 of the target (reference object 3) coincides with the y axis by the reference object control unit 6, the image coordinates corresponding to the reference points A, B, and O are only y coordinates. Scan along a line that passes through the center of the image to obtain y coordinates y ₁ , y ₂ , y ₀ of image coordinates P ₁ , P ₂ , P ₀ , respectively.

  S15, S16: The geometric measurement control unit 7 controls the inclination of distance measurement and the measurement of geometric information. Here, the slope control of the distance measurement of S15 is performed by the processing processes of S41 to S45 in FIG. 16, and the geometric information of S16 is measured by the processing processes of S46 to S48. After the processing in the reference object control unit 6 is completed, the geometric measurement control unit 7 controls the attitude of the laser distance measurement unit 10 shown in FIG. 8 so that the laser of the laser distance measurement unit 10 faces the camera 5. To do.

  If it demonstrates based on FIG. 16, when a process is started first, the measurement attitude | position (swing angle Ω, inclination angle (elevation angle) Ψ) of the laser distance measurement part 10 will be initialized (swing angle Ω and Means an angle in the horizontal direction orthogonal to the tilt angle (elevation angle) Ψ, and the laser distance measuring unit 10 is directed toward the target camera 5 by rotation control of these two angles. Here, the initial value of the tilt angle (elevation angle) Ψ representing the vertical angle is set to 0 degrees indicating the horizontal direction, and the center position is set to the initial value of the swing angle Ω representing the horizontal angle. It is assumed that the posture is changed symmetrically from the center position (S41).

  Next, the minute rotation angle Δω is increased to the swing angle Ω (S42), and the minute rotation angle Δψ is increased to the tilt angle (elevation angle) Ψ (S43). As a result of the processing in steps S42 and S43, if the value of the tilt angle (elevation angle) Ψ is within the range (below the upper limit value) (S44), distance measurement is performed in this posture (S46).

  That is, in laser distance measurement, a semiconductor laser is usually used frequently, and a red point shines at the laser destination. The distance L from the measurement position (or measurement point) to the camera 5 is measured by pinpoint measurement using the reflection of the laser.

  An image is acquired in synchronization with the measurement of the distance L (S47). If a red pattern indicating that the laser has been irradiated in this image is observed on the image, it means that the direction of the laser distance measuring unit 10 is directed toward the camera 5. In this way, the presence or absence of laser light detection is determined (S48). If there is no change in the image due to the laser irradiation, the process returns to S43, and the minute rotation angle Δψ is further increased to the tilt angle (elevation angle) ψ, and the presence or absence of similar laser light detection is determined in that posture. If the value of the tilt angle (elevation angle) ψ is out of the range (above the upper limit) as a result of increasing the minute angle Δψ (S44), the tilt angle (elevation angle) ψ is initialized (S45). Further, the minute rotation angle Δω is increased to the swing angle Ω (S42), and the same determination processing as before is continued. When it is determined in S48 that the laser beam is detected, the distance L and the tilt angle (elevation angle) Ψ at that time are temporarily secured, and the next camera calibration processing unit 7 (S17 in FIG. 6, S17 in FIG. 16). Proceed to S49).

S17: The camera calibration processing unit 8 executes camera calibration processing, that is, S49 to S51 in the processing process of FIG. First, from the geometric information (distance L and tilt angle (elevation angle) Ψ) obtained by the laser measurement, the camera tilt angle φ (= Ψ−π / 2) and the depth d = Lcos (φ) shown in FIG. Heights h = Lsin (φ) with respect to point A are calculated (S49). Next, y coordinates: y ₁ , y ₂ , y _{0 of} the image coordinates p ₁ , p ₂ , p ₀ (image coordinates measured in S14) corresponding to the reference points A, B, O, the geometrical information of the camera 5 Since the tilt angle φ (the tilt angle φ obtained in S49) has been obtained, the focal length f of the camera 5 is obtained using the relationship of the equations (13) and (15) (S50). Finally, as shown in FIG. 3, the camera viewpoint position (Tx, Ty, Tz) = (0, h + h) using the reference point O as the origin of the world coordinate system from the known h ₁ and h and d obtained in S49. ₁ , d) is calculated (S51).

  As described above, the target (reference object 3) designed in FIG. 8 or FIG. 11 is used as a photographic subject for calibration, and processing is performed according to the basic configuration diagram of FIG. The camera viewpoint position (Tx, Ty, Tz), the camera optical axis rotation angle θ, the tilt angle φ, and the focal length f of the camera 5 can be obtained.

  In the first embodiment, since camera calibration is performed using a small number of reference points, a sufficient amount of reference points for calibration is not required unlike conventional camera calibration (Non-Patent Documents 1 and 2). In the first embodiment, the special reference object 3 is used to smoothly measure the coordinate values of the reference points A, B, and O on the image, thereby simplifying the camera calibration operation and shortening the processing time. Can be planned. Further, if a plurality of cameras 5 are arranged so as to surround the reference object 3, the plurality of cameras 5 can be calibrated at the same time, so that seamless 3D video generation or arbitrary viewpoint video generation using a multi-viewpoint camera is possible. Contribute.

[Embodiment 2]
Before describing the second embodiment, the technical problems of the second embodiment will be supplemented. In the first embodiment, when the distance between the camera 5 and the reference object 3 is sufficiently large, it is assumed that the measurement point approximately coincides with the point A (the measurement point at the time of laser distance measurement is the reference point A). When the distance between the camera 5 and the reference object 3 is short, the approximation used in the first embodiment is not valid.

  However, it is difficult to observe the measurement points of the laser distance measuring device 10 on the image. Therefore, in the second embodiment, as shown in FIG. 17, when the difference Δh between the reference point A and the measurement point in the laser measurement cannot be ignored, the inclination angle (elevation angle) Ψ obtained by the geometric measurement control unit 7, The camera parameters are corrected and calculated using the depth d and height h calculated by the camera calibration processing unit 8.

  In FIG. 17, the following equations (17) and (18) are established from the geometric relationship.

  When the addition theorem is used in the above equation (18) and expanded and arranged using the above equation (17), the following equation (19) is obtained.

  From the relationship between the above formula (18) and the above formula (19), the following formula (20) is derived.

  Therefore, if the difference Δh in height between the reference point A and the laser measurement point is given, the difference in tilt angle (hereinafter referred to as a correction angle) ΔΨ in FIG. 17 can be calculated by the following equation (21).

  In the second embodiment, the correction angle ΔΨ according to the above equation (21) is calculated from the geometric information obtained by the laser distance measuring unit 10, and the camera parameter is corrected using the correction angle ΔΨ.

Although the basic configuration of the second embodiment is the same as that of the first embodiment, the calculation in the camera calibration processing unit 8 is slightly different, and a flowchart showing the processing is shown in FIG. Assume that the image of FIG. 14 is obtained through the control of the reference object control unit 6 as in the first embodiment. Since the vertical bar 9 of the reference object 3 coincides with the y axis, the reference point detection unit 4 uses y ₁ , y ₂ , y as y coordinates on the image coordinates corresponding to the reference points A, B, O, respectively. _{Get 0} . Further, the geometric measurement control unit 7 measures the distance L and the tilt angle (elevation angle) Ψ between the laser distance measuring device 10 and the camera 5 by laser measurement.

Next, the camera calibration processing unit 8 obtains the depth d, the camera tilt angle φ, and the height h from the relationship of the trigonometric functions. It is assumed that Δh is acquired in advance by another surveying means. In the second embodiment, the correction angle ΔΨ according to the above equation (21) is calculated from the geometric information obtained by the laser distance measuring unit 10, and the tilt angle Ψ + ΔΨ when viewed from the reference point A is obtained (S52). The camera tilt angle φ = (Ψ + ΔΨ−π / 2) corrected from the tilt angle Ψ + ΔΨ is calculated (S53). The y coordinates on the image coordinates (p ₁ , p ₂ , p ₀ ) corresponding to the reference points A, B, and O are y ₁ , y ₂ , and y ₀ , respectively, and the corrected camera tilt angle φ = (Ψ + ΔΨ -Π / 2) is substituted into the equations (13) and (15) to obtain the focal length f of the camera 5 (S54). Further, as shown in FIG. 17, the camera viewpoint position (Tx, Ty, Tz) = (0, h + h ₁ + Δh, d) is output so that the reference point O is the origin of the world coordinate system (S55). .

  As described above, even in the situation shown in FIG. 17, according to the second embodiment, the camera viewpoint position (Tx, Ty, Tz), the camera optical axis rotation angle θ, the tilt angle φ, and the focal length f of the camera. Can be requested. As a result, the second embodiment has the same effects as the first embodiment.

  Further, according to the second embodiment, it is possible to perform camera calibration even when the distance between the camera 5 and the reference object 3 is short.

<Programs>
The present invention can also be configured as a program for causing a computer to function as a part or all of each means of the camera calibration apparatus 1. In this case, the computer is caused to execute all or some of steps S12 to S17, S21 to S25, S31 to S35, S41 to S51, and S52 to S55.

  This program can be provided through a network such as a website or e-mail. The program can be recorded on a recording medium such as a CD-ROM, DVD-ROM, CD-R, CD-RW, MO, HDD, Blu-ray Disk (registered trademark), and stored and distributed. is there. This recording medium is read using a recording medium driving device, and the program code itself executes the processing of the above-described embodiment, so that the recording medium also constitutes the present invention.

DESCRIPTION OF SYMBOLS 1 ... Camera calibration apparatus 3 ... Reference object 4 ... Reference point detection part 5 ... Camera (imaging apparatus)
6 ... Reference object control unit 7 ... Geometric measurement control unit 8 ... Camera calibration processing unit θ ... Optical axis rotation angle Ψ ... Elevation angle L ... Distance A, B, O ... Reference point

Claims (6)

A camera calibration device that calibrates external parameters including the internal parameters and orientation and position of an imaging device from an image acquired from a single eye or a plurality of imaging devices,
Reference point detection means for detecting image coordinates of reference points arranged in a straight line in a reference object having a known shape from the image;
Calculates the optical axis rotation angle between the line segment formed from the reference point and the reference axis on the image coordinates, and reversely rotates the image around the origin of the image coordinates according to the calculated optical axis rotation angle And reference object control means for moving the position of the reference object so that one of the reference points coincides with the origin of the image coordinates;
Geometric measurement means for measuring an elevation angle and a distance between the imaging device and the measurement device by a measurement device provided on the reference object;
Using the projective geometric relationship between the reference point and the imaging device, imaging is performed from the elevation angle and distance between the imaging device and the distance measuring device, the optical axis rotation angle, and the image coordinates of the reference point detected after the reference object control. Camera calibration means for calibrating the internal and external parameters of the device;
A camera calibration device comprising: The camera calibration means includes
An elevation angle between the imaging device and the measurement device is corrected to an elevation angle between the imaging device and one of the reference points, and internal parameters and external parameters of the imaging device are calibrated based on the corrected elevation angle. The camera calibration device according to claim 1. A camera calibration method for calibrating external parameters including an internal parameter and orientation and position of an imaging device from an image acquired using a single eye or a plurality of imaging devices,
A reference point detecting step in which a reference point detecting means detects image coordinates of a reference point arranged in a straight line in a reference object having a known shape from the image;
A reference object control unit calculates an optical axis rotation angle between a line segment formed from the reference point and a reference axis on the image coordinates, and the image is converted into image coordinates according to the calculated optical axis rotation angle. A reference object control step that reversely rotates around the origin and moves the position of the reference object so that one of the reference points coincides with the origin of the image coordinates;
A geometric measurement step in which a geometric measurement means measures an elevation angle and a distance between the imaging device and the measurement device by a measurement device provided on the reference object;
An image of the reference point detected by the camera calibration means after the control of the elevation angle and distance between the imaging device and the measuring device, the optical axis rotation angle, and the reference object, using the projective geometry relationship between the reference point and the imaging device. A camera calibration step for calibrating the internal and external parameters of the imaging device from the coordinates;
A camera calibration method characterized by comprising: The camera calibration step includes
An elevation angle between the imaging device and the measurement device is corrected to an elevation angle between the imaging device and one of the reference points, and internal parameters and external parameters of the imaging device are calibrated based on the corrected elevation angle. The camera calibration method according to claim 3.   A camera calibration program for causing a computer to function as the camera calibration device according to claim 1.   6. A recording medium on which the camera calibration program according to claim 5 is recorded.

Images