CN113446934A - Close-range photogrammetry rotatable code calibration equipment and calibration method - Google Patents
Close-range photogrammetry rotatable code calibration equipment and calibration method Download PDFInfo
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- CN113446934A CN113446934A CN202110619501.8A CN202110619501A CN113446934A CN 113446934 A CN113446934 A CN 113446934A CN 202110619501 A CN202110619501 A CN 202110619501A CN 113446934 A CN113446934 A CN 113446934A
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Abstract
The invention discloses a close-range photogrammetry rotatable code calibration device and a calibration method, wherein the calibration device comprises a code block, a detection tag, a first magnet and a target ball, the code block is adhered to one side of the detection tag, the other side of the detection tag is adsorbed on the target ball through the first magnet, and the detection tag can rotate in any direction on the spherical surface of the target ball by taking the spherical center of the target ball as the center; the coding block performs preset multi-posture rotation on the target ball through the detection tag, and a camera performs corresponding photographing of each posture to form a plurality of measured photographing pictures; the position of the coding point of the coding block in each measured shot picture is identified, and the target sphere center coordinate is calculated by a least square fitting method. The invention can solve the problems of limitation and insufficient flexibility of close-range photogrammetry influenced by the coding blocks, reduce the number of the coding blocks for photogrammetry and improve the measurement efficiency.
Description
Technical Field
The invention relates to the field of precision engineering measurement, in particular to a close-range photogrammetry rotatable code calibration device and a calibration method.
Background
When using close-range photogrammetry systems for precision measurements, fixed code blocks are used, as shown in fig. 1. The code blocks are typically 50mm by 1mm special reflective marker paper blocks which are attached in fixed positions by strong adhesive on the back. The coding blocks are fixed once being pasted to the preset positions in field use, and more coding blocks need to be arranged in order to guarantee the picture splicing requirement and meet the requirement of meeting the field measurement precision in multi-angle measurement. Particularly, when the measurement is carried out in a narrow space, the process of arranging the coding blocks is complicated and time-consuming, and the field measurement work is difficult.
Disclosure of Invention
The invention aims to provide a close-range photogrammetry rotatable code calibration device and a calibration method. The invention can solve the problems of limitation and insufficient flexibility of close-range photogrammetry caused by the influence of the coding block.
The invention relates to a close-range photogrammetry rotatable code calibration device which realizes one of the purposes of the invention, and is characterized in that: a close-range photogrammetry rotatable code calibration device is characterized in that: the detection device comprises a coding block, a detection tag, a first magnet and a target ball, wherein the coding block is adhered to one side of the detection tag (2), the other side of the detection tag is adsorbed on the target ball through the first magnet, and the detection tag can rotate in any direction on the spherical surface of the target ball by taking the spherical center of the target ball as the center;
the coding block performs preset multi-posture rotation on the target ball through the detection tag, and a camera performs corresponding photographing of each posture to form a plurality of measured photographing pictures;
the position of the coding point of the coding block in each measured shot picture is identified, and the target sphere center coordinate is calculated by a least square fitting method.
The calibration method for the close-range photogrammetry rotatable code, which realizes the second purpose of the invention, comprises the following steps:
step 1, a coding block performs preset multi-posture rotation on a target ball through a detection tag, and takes pictures of corresponding angles and postures through a camera to acquire a plurality of pictures;
the preset multi-posture rotation comprises a reference posture of the coding block with a horizontal angle of 0 degree and a vertical angle of 0 degree;
step 2, calculating the gradient value of each pixel point in each picture, and identifying the position information of the coding point on the coding block in each picture according to the gradient value of each pixel point;
and 4, calculating the center coordinates of the target ball by a ball fitting method for the circle center position coordinate information of each coding point of the coding blocks in all the pictures, thereby determining the position relationship between the circle center position of each coding point of the coding blocks in all the pictures and the center coordinates of the target ball to realize the calibration of the codes.
The invention can directly use the close-range photogrammetry method to accurately calibrate the relative relation between the coding block mark point and the target ball center, thereby rotating the detection label in any direction during field measurement, reducing the number of coding blocks used in photogrammetry and improving the measurement efficiency.
Drawings
FIG. 1 is a schematic diagram of a coding block according to the present invention;
FIG. 2 is a schematic diagram of a rotatable code calibration apparatus according to the present invention;
in the figure, 1 is a coding block, 2 is a detection label, 3 is a first magnet, 4 is a first clamping ring, 5 is a target ball, 6 is a second clamping ring, 7 is a second magnet, 8 is a sealing ring and 9 is a base;
FIG. 3 is a front view of a rotatable code calibration apparatus according to the present invention;
FIG. 4 is a left side view of the rotatable code calibration apparatus of the present invention;
FIG. 5 is a schematic view of a base of the rotatable code calibration apparatus of the present invention;
in the figure, 6-second clamping ring, 7-second magnet, 8-sealing ring, 9-base and 10-base protective cover;
FIG. 6 is a plane coordinate position of the image edge contour image calculated by the encoding points according to the present invention;
fig. 7 shows the coordinates of each encoded point recorded by IDPMS software and the calculated coordinates of the center of the target sphere.
Detailed Description
The following detailed description is provided for the purpose of explaining the claimed embodiments of the present invention so that those skilled in the art can understand the claims. Details not described in this specification are within the skill of the art that are well known to those skilled in the art. The scope of the invention is not limited to the following specific implementation configurations. It is intended that the scope of the invention be determined by those skilled in the art from the following detailed description, which includes claims that are directed to this invention.
In operation, the sectional view of the close-range photogrammetry rotatable code calibration apparatus is shown in fig. 2 and 4, and the front view and the left view are respectively shown in fig. 3 and 4, which comprises: the detection device comprises a coding block 1, a detection tag 2, a first magnet 3 and a target ball 5, wherein the coding block 1 is adhered to one side of the detection tag 2, the other side of the detection tag 2 is adsorbed on the target ball 5 through the first magnet 3, and the detection tag 2 can rotate on the spherical surface of the target ball 5 in any direction by taking the sphere center of the target ball 5 as the center;
the encoding block 1 performs preset multi-posture rotation on the target ball 5 through the detection tag 2, and takes pictures of corresponding postures through a camera to form a plurality of measured shot pictures;
and (3) calculating to obtain the center coordinates of the target sphere by identifying the position of the coding point of the coding block 1 in each measured and shot picture and by a least square fitting method.
In this embodiment, the coding blocks 1 are specially-made reflective mark paper blocks of 50mm by 0.5mm, the coding points on the coding blocks 1 are point-like coding marks, and the point-like coding marks form digital codes according to different distributions of the points on a plane, as shown in fig. 1.
The setting rule of the coding points on the coding block 1 is as follows:
the code point arrangement on the coding block has uniqueness, namely different code point arrangements correspond to unique codes, so that the same codes cannot be generated.
In this embodiment, the target ball 5 is a finish-machined target ball with a diameter of 38.1mm, and a tool made of a stainless steel 440C material has a machining error of better than 5 micrometers and is used as a reference for detecting the rotation of the label.
The close-range photogrammetry rotatable code calibration equipment further comprises: second magnet 7, base 9 and base visor 10, target ball 5 passes through second magnet 7 and adsorbs in base 9, and base visor 10 covers in the whole surface of base 9.
The close-range photogrammetry rotatable code calibration equipment further comprises: the magnetic detection tag further comprises a first clamping ring 4 and a second clamping ring 6, wherein the first clamping ring 4 is arranged in a clamping groove in the detection tag 2 and used for fixing the first magnet 3, and the second clamping ring 6 is arranged in a clamping groove in the base 9 and used for fixing the second magnet 7.
A sealing ring 8 is arranged between the second magnet 7 and the base 9 and is used for filling a gap between the base protective cover 10 and the base 9 when the base protective cover is installed on the base 9.
The calibration method for the close-range photogrammetry rotatable code comprises the following steps:
step 1, a coding block 1 performs preset multi-posture rotation on a target ball 5 through a detection tag 2, and takes pictures of corresponding angles and postures through a camera to form a plurality of pictures;
the shooting postures of the coding block in the embodiment are shown in the following table 1, and 15 postures are provided.
TABLE 1
| Serial number | Posture | Horizontal angle | Vertical angle |
| 1 | A | 0° | 0° |
| 2 | II | 45° | 0° |
| 3 | III | 90° | 0° |
| 4 | Fourthly | 135° | 0° |
| 5 | Five of them | 180° | 0° |
| 6 | Six ingredients | 225° | 0° |
| 7 | Seven-piece | 270° | 0° |
| 8 | Eight-part | 315° | 0° |
| 9 | Nine- |
0° | 45° |
| 10 | Ten pieces of cloth | 60° | 45° |
| 11 | Eleven points of the design | 120° | 45° |
| 12 | Twelve aspects | 180° | 45° |
| 13 | Thirteen-layer rubber | 240° | 45° |
| 14 | Fourteen-layer | 300° | 45° |
| 15 | Fifteen items of |
0° | 90° |
Note:
1. the horizontal angle of 0 degrees is the horizontal angle of the normal line of the plane of the coding block at the first direction of the horizontal rotation of the target ball, which is defined as 0 degrees, and the other horizontal angles are the angles of the normal line of the plane of the coding block which rotates clockwise from the horizontal direction of 0 degrees.
2. The vertical direction angle is the included angle between the normal line of the target ball coding block plane and the horizontal plane, and the included angle is positive upwards and negative downwards.
3. The encoded block data of multiple postures can be obtained by measuring according to the postures of the encoded balls in the table 1, and the data is used for calculating the center of the encoded ball relative to the encoded block, so that a high-precision measurement result can be obtained.
The preset multi-posture rotation comprises a reference posture of the coding block 1 with a horizontal angle of 0 degree and a vertical angle of 0 degree;
step 2, calculating the gradient value of each pixel point in each picture, and identifying the position information of the coding point on the coding block 1 in each picture according to the gradient value of each pixel point;
in the step, a canny operator is used for calculating the gradient value of each pixel point in each picture, and the position information of the coding point on the corresponding coding block 1 is identified according to the gradient value of each pixel point.
Detecting the point positions of the coding blocks by adopting Canny operators of a convolution template of 3 multiplied by 3 at the coding points on the coding blocks, and calculating the gradient Gx in the x direction and the gradient Gy in the y direction of the horizontal and vertical coordinates (i and j) of the pixel points;
i.e. the gradient components are:
wherein f (i-1, j +1) represents the pixel value corresponding to the coordinate (i-1, j + 1);
the gradient amplitude is:
the gradient direction is as follows:
α(x,y)＝atan(Gy/Gx)。
in this embodiment, pixel points with gradient values greater than 50 and less than 150 calculated according to the canny operator are considered as pixel points of the edge contour of the coding point on each coding block 1.
although the encoding point is a circular mark, the image of the encoding point on the image plane is a plane ellipse, so the position of the center of the encoding point can be determined by performing ellipse least square fitting on the extracted edge points. The general equation for a planar ellipse is:
x2+2Bxy+Cy2+2Dx+2Ey+F＝0
the ellipse fitting can find the 5 parameters B, C, D, E and F of the ellipse equation shown above (B, C, D, E and F are coefficients of any ellipse equation, x and y are coordinates of points on the ellipse curve, the general equation contains the rotation and translation transformation of the standard ellipse), and the ellipse center coordinate calculation formula is as follows:
the coordinates of the center of the ellipse are the coordinates of the center point of the code, and the coordinates of the center position of each code point in the code block 1 can be calculated according to the formula.
And 4, calculating the center position coordinates of the coded points of each coded point of the coding block 1 in all the pictures by a least square ball fitting method to obtain the center coordinates of the target ball 5, thereby determining the position relationship between the center position coordinate information of each coded point in the coding block 1 in all the pictures and the center coordinates of the target ball 5 to realize the calibration of the codes.
The coded sphere is rotated for 15 postures, a camera is used for shooting a coded block, namely 15 groups of points are shot, and the coordinates O1 of the center of the target sphere can be calculated by a method of least square fitting the sphere by the 15 groups of points. Therefore, the relative attitude relation data of the target ball center on the coding block on the surface of the detection label can be obtained through the rotation calculation of the coding block.
Based on the obtained coordinates of the center of the target ball 5 and the coordinate information of the photographed reference attitude, a data template including coordinates of coded points NUGGET1_3 to NUGGET1_ D on the code blocks and coordinates of the center of the target ball O1 as reference data for calculating the center of the target ball at the time of field measurement is generated using the photogrammetry software IDPMS image scanning adjustment calculation function, as shown in fig. 7.
When the coordinate transformation device is used on site, the coordinate transformation is needed to be carried out according to the template data in order to obtain the coordinates of the central point of the target ball under the site measurement coordinate system. The conversion method is to convert the sphere center coordinate under the template coordinate system into the coordinate under the field measurement coordinate system by using a common point conversion method. In the conversion process, the relationship between the common point (encoding block point) and the coordinate system (template coordinate system) where the common point is located is fixed. Two different coordinate systems exist for two groups of common points (encoding block points) under a field measurement coordinate system and a module coordinate system, so that three translation parameters and three rotation parameters exist between the two coordinate systems, and the three translation parameters and the three rotation parameters are recorded as t ═ X0,Y0,Z0,εx,εy,εz) Wherein X is0、Y0、Z0As a translation parameter,. epsilonx、εy、εzIs a coordinate system rotation angle parameter. Let the coordinates of the common point (encoding block point) in the template coordinate system be (X, Y, Z), and the coordinates in the field measurement coordinate system be (X ', Y ', Z '), the transformation relationship is:
for the parameters of the rotation matrix in the following formula, see above, therefore, for the ith common point (x)i',yi',zi') the following fitting equation can be listed:
in the above formula (X)i,Yi,Zi) The coordinates of the ith common point in the template coordinate system. Theoretically, if there are more than 3 common points, the coordinate system transformation parameter X can be obtained0、Y0、Z0、εx、εy、εz. The transformation parameters of the coordinate system can be calculated from the common points (coding block points). And calculating the coordinates of the target ball center in the field measurement coordinate system through a conversion relation formula according to the conversion parameters and the coordinates of the target ball center in the template coordinate system.
Claims (8)
1. A close-range photogrammetry rotatable code calibration device is characterized in that: the detection device comprises a coding block (1), a detection tag (2), a first magnet (3) and a target ball (5), wherein the coding block (1) is adhered to one side of the detection tag (2), the other side of the detection tag (2) is adsorbed on the target ball (5) through the first magnet (3), and the detection tag (2) can rotate in any direction on the spherical surface of the target ball (5) by taking the spherical center of the target ball (5) as the center;
the encoding block (1) performs preset multi-posture rotation on the target ball (5) through the detection tag (2), and takes pictures of corresponding postures through a camera to form a plurality of measured shot pictures;
the position of the coding point of the coding block (1) in each measured shot picture is identified, and the center coordinates of the target ball are obtained through calculation.
2. The close-up photogrammetry rotatable code calibration apparatus of claim 1, wherein: the setting rule of the coding points on the coding block (1) is as follows:
the code point arrangement on the coding block has uniqueness, namely different code point arrangements correspond to unique codes, so that the same codes cannot be generated.
3. The close-up photogrammetry rotatable code calibration apparatus of claim 1, wherein: it still includes second magnet (7), base (9) and base visor (10), target ball (5) adsorb in base (9) through second magnet (7), and base visor (10) cover is on the whole surface of base (9).
4. The close-up photogrammetry rotatable code calibration apparatus as claimed in claim 1 or 2, wherein: the magnetic detection tag further comprises a first clamping ring (4) and a second clamping ring (6), wherein the first clamping ring (4) is arranged in a clamping groove in the detection tag (2) and used for fixing the first magnet (3), and the second clamping ring (6) is arranged in a clamping groove in the base (9) and used for fixing the second magnet (7).
5. The close-up photogrammetry rotatable code calibration apparatus of claim 5, wherein: a sealing ring (8) is arranged between the second magnet (7) and the base (9), and the sealing ring (8) is used for filling a gap between the base protective cover (10) and the base (9) when the base protective cover is installed on the base (9).
6. A calibration method of a close-range photogrammetry rotatable code is characterized by comprising the following steps:
step 1, a coding block (1) performs preset multi-posture rotation on a target ball (5) through a detection tag (2), and takes pictures of corresponding angles and postures through a camera to form a plurality of pictures;
step 2, calculating the gradient value of each pixel point in each picture, and identifying the position information of the coding point on the coding block (1) in each picture according to the gradient value of each pixel point;
step 3, performing ellipse least square fitting on the extracted position information of the coding points, thereby determining the circle center position information of each coding point in the coding block (1) of each picture;
and 4, calculating the center coordinates of the target ball (5) according to the circle center position information of each coding point of the coding block (1) in all the pictures by a least square ball fitting method, thereby determining the position relationship between the circle center position of each coding point of the coding block (1) in all the pictures and the center coordinates of the target ball (5) to realize the calibration of the codes.
7. The method for calibrating a close-up photogrammetry rotatable code as claimed in claim 6, wherein: in the step 2, the canny operator is used for calculating the gradient value of each pixel point in each picture, and the position information of the coding point on the corresponding coding block (1) is identified according to the gradient value of each pixel point.
8. The method for calibrating a close-up photogrammetry rotatable code as claimed in claim 7, wherein: in the step 2, the coding points on the coding block adopt Canny operators of a convolution template of 3 x 3 to detect the positions of the coding block points, and the x-direction gradient Gx and the y-direction gradient Gy of the horizontal and vertical coordinates (i and j) of the pixel points are calculated;
i.e. the gradient components are:
Gx＝{[f(i-1,j+1)-f(i-1,j-1)]+[f(i,j+1)-f(i,j-1)]+[f(i+1,j+1)-f(i+1,j-1)]}/3
Gy＝{[f(i-1,j-1)-f(i+1,j-1)]+[f(i-1,j)-f(i+1,j)]+[f(i-1,j+1)-f(i+1,j+1)]}/3
wherein f (i-1, j +1) represents the pixel value corresponding to the coordinate (i-1, j + 1);
the gradient amplitude is:
the gradient direction is as follows:
α(x,y)＝atan(Gy/Gx)。
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