CN101916457B - Datum volume and point cloud synthesis method for 3D point cloud data acquisition - Google Patents

Abstract

The invention discloses a reference body for three-dimensional point cloud data acquisition, which includes a base, a support shaft perpendicular to the base is fixed in the center of the base, and at least two metal spheres placed up and down are arranged on the support shaft. The connection is fixed and welded by the connecting shaft; there is a sandblasting layer on the surface of the sphere; the invention also provides a method of using the above-mentioned reference body to determine the central rotation axis of the turntable, and splicing the local three-dimensional point cloud according to the calculated central rotation axis, and synthesizing it into a complete A method for 3D point cloud images. The invention obtains dense three-dimensional point cloud data through the reference body with little loss, has fast synthesis speed and high synthesis precision when synthesizing the three-dimensional point cloud, and the synthesized image is clear and complete without ghosting.

Description

Datum volume and point cloud synthesis method for 3D point cloud data acquisition

technical field

The invention relates to the technical field of computer vision three-dimensional scanning and detection, in particular to a reference body for acquiring three-dimensional point cloud data and a point cloud synthesis method.

Background technique

The acquisition of 3D point cloud data refers to obtaining the shape and structure of the object through 3D digital technology. High-precision point cloud data can better represent the 3D shape characteristics of the measured object. Development, rapid prototyping of antiques, handicrafts, sculptures, portrait products, etc., mechanical shape design, medical plastic surgery, human body shape production, human body shape measurement and plant shape acquisition and other fields have important applications.

The more conventional way to obtain point cloud data is to use a 3D laser scanner to obtain 3D point cloud data. Although this method is more flexible in obtaining data and can obtain the final point cloud while scanning, the defect of this technical solution is that when obtaining an object with a more complex shape, the acquisition speed is slow, the data is lost, the point cloud is sparse, and the acquired Point cloud data has no color, which is not conducive to post-processing such as synthesis of 3D point cloud data. Another acquisition method is the structured light method, that is, the light emitted by the projector passes through the optical system to form points, lines, coded patterns, etc. The parameters are calculated to obtain the depth image of the surface of the scene, and the three-dimensional coordinate value of the object surface is further calculated.

Ren Qing, Diao Changyu, Lu Dongming, and Liu Gang disclosed a 3D reconstruction system based on projection coded structured light in the document "3D Reconstruction of Cultural Relics Based on Structured Light" (Dunhuang Research, 2005, 93(5): 102-106). The principle is to reconstruct based on structured light, project a group of structured light into a three-dimensional scene, and extract the three-dimensional shape of the object by analyzing the projection changes of different coded structured lights on the object; the three-dimensional scanning system based on the principle of structured light generally consists of the following Partial composition: CNC turntable, high-precision 3D texture information acquisition terminal, 3D data processing computer, 3D information acquisition terminal, 3D information acquisition software. The method of synthesizing the 3D point cloud through this system is to place the object on the CNC turntable to obtain point cloud data from different angles, and then use the reference point method to stitch the point clouds from different angles to synthesize a complete 3D point cloud. Although the accuracy of the point cloud at a certain angle obtained by this method is very high each time, and the accuracy of the CNC turntable is also very high, its defect is that because a complete three-dimensional point cloud is synthesized by hand in the end, it is difficult to synthesize some complex objects. For objects such as living plants, the accuracy of the synthesized 3D point cloud is low.

Long Xi, Zhong Yuexian, Li Renju, and You Zhifu also published a paper "3D Mosaic Technology for Structured Light 3D Scanning Measurement" (Journal of Tsinghua University (Natural Science Edition), 2002, 42(4): 477-480). A new 3D stitching technology, which uses a stepping motor-driven rotary table to stitch data point clouds of different fields of view to provide complete 3D information on the surface of the part, but this paper does not provide the specific details of the rotary table shaft. However, in practice, the naked eye and the mouse are used to find and determine the reference points in the point cloud, and the resulting 3D point cloud has low precision and often has obvious ghosting.

Contents of the invention

The invention provides a reference body for three-dimensional point cloud data acquisition, which is used to determine the central rotation axis of a rotary table, and solves the problem of low precision and incompleteness of three-dimensional point cloud synthesized by a reference point method in the prior art.

A reference body for three-dimensional point cloud data acquisition, including a base, a support shaft perpendicular to the base is fixed in the center of the base, and at least two metal spheres placed up and down are arranged on the support shaft, and the spheres pass through The connecting shaft is fixedly connected; the surface of the sphere has a sandblasting layer.

The spherical profile of the sphere is 0.05, and the surface roughness is 3.2-6.3.

The sphere material is selected from one of bearing steel, iron alloy and cast iron.

Preferably, the number of spheres is two or more than three.

The reference body in the present invention has no requirements on the internal structure of the sphere, generally a solid sphere can be used, but it has high requirements on the surface of the sphere, mainly including the two parameters of spherical profile and surface roughness, wherein the spherical profile It represents the processing accuracy of the sphere, and the surface roughness represents the surface treatment effect of the sphere, both of which are the main factors affecting the effect of 3D point cloud synthesis. Therefore, the present invention adopts a sandblasting process to carry out sandblasting treatment on the metal surface of the sphere, so that the treated sphere can not only maintain the original processing accuracy of the metal sphere, but also overcome the problem that the surface of the sphere is too smooth when the processing accuracy of the metal material is high. , which is not conducive to the technical defect of obtaining the spherical shape point cloud in the way of structured light. In the present invention, the surface of the sphere after sandblasting treatment has a spherical profile of 0.05 and a surface roughness of 3.2 to 6.3, so that the acquisition effect of the 3D point cloud data of the sphere shape is better, which is beneficial to the synthesis of the 3D point cloud.

The sand blasting process adopts the existing technology, that is, compressed air is used as the power to form a high-speed jet beam to spray the spray material (copper ore, quartz sand, corundum, iron sand, sea sand) to the surface of the workpiece to be treated at high speed, so that the surface of the workpiece The appearance or shape of the workpiece changes; due to the impact and cutting effect of the abrasive on the surface of the workpiece, the surface of the workpiece obtains a certain degree of cleanliness and different roughness, and the mechanical properties of the workpiece surface are improved, thus improving the fatigue resistance of the workpiece. Increase the adhesion between the workpiece and the coating, prolong the durability of the coating film, and also benefit the leveling and decoration of the coating.

The present invention also provides a method for using the reference body to determine the central axis of rotation of the turntable for three-dimensional point cloud synthesis, which solves the problems of slow point cloud synthesis, difficulty in finding reference points, and low synthesis accuracy in the prior art.

Due to the use of different spheres in the late stage three-dimensional point cloud synthesis processing, the point cloud synthesis algorithm of two spheres is different from the point cloud synthesis algorithm of three and more than three spheres, so the point cloud synthesis algorithm in the present invention is mainly The two-sphere reference body and the three-sphere reference body are described.

A point cloud synthesis method mainly includes the following steps:

(1) Place the reference body on a turntable that can precisely control the rotation angle, and scan the reference body with a three-dimensional structured light scanner;

(2) The turntable scans once every 90 degrees to obtain a point cloud at an angle of the spherical surface, that is, a local spherical point cloud. Four sets of local spherical point clouds located at the upper and lower two groups of squares with a total of 8 vertices are obtained by accumulative scanning four times, and calculated the central shaft of the turntable;

(3) Place the object to be tested on a turntable that can precisely control the rotation angle, and scan the object to be tested with a three-dimensional structured light scanner. The turntable scans once every time it rotates, and the rotation angle of the turntable can be adjusted according to different objects to be tested. Scan to get several 3D point cloud data;

(4) Using the central axis of rotation of the turntable calculated in step (2), the 3D point cloud data scanned in step (3) is used to splice the 3D point cloud data to synthesize a complete 3D point cloud.

The calculation method of the central rotating shaft of the turntable in the described step (2) is as follows:

1) According to the local spherical point cloud of each scan, the center of each sphere is calculated. Each scan can obtain the upper and lower two sphere centers, and four scans can obtain the upper and lower two sets of four sphere centers located at the four vertices of a square;

2) Connect the center of the upper sphere of the reference body located at the diagonal of the square to obtain two intersecting diagonal lines;

3) Connect the center of the lower sphere of the reference body located at the diagonal of the square to obtain two intersecting diagonal lines;

4) Calculate the intersection points A(x _a , y _a , z _a ) and B(x _b , y _b , z _b ) of the upper and lower pairs of intersecting diagonals;

5) Connect point A and point B to obtain the central axis of rotation of the turntable.

Similarly, when the three-sphere reference body is calculated according to the calculation method of the central rotation axis of the above-mentioned turntable, multiple points on the central rotation axis can be obtained. At this time, the calculation from multiple points to the rotation axis is equivalent to the straight line fitting calculation of points in a limited three-dimensional space. The algorithm can adopt the algorithm proposed by Xi Yang in the document "A Method for Spatial Straight Line Fitting" (Journal of Qiqihar University, 2009, 25(2): 64-67).

"Synthetic complete three-dimensional point cloud" of step (4) in the point cloud synthesis method of the present invention refers to the calculation of rotating around a fixed axis, and the algorithm can adopt Sun Jiaguang and Yang Changgui in the book "Computer Graphics" (Tsinghua University Press, 1995 Algorithm presented in May 2nd Edition, ISBN 7-302-01708-5/TP.746, P346-348).

The reference body used for acquiring 3D point cloud data provided by the present invention has high processing precision and the metal surface of the sphere is sandblasted, so that the 3D point cloud data acquired by the structured light method is dense and less lost, which is beneficial to the later 3D point cloud synthesis processing .

The present invention determines the central axis of rotation of the rotary table through the reference body, splices the local three-dimensional point cloud according to the calculated central axis, and synthesizes it into a complete image. When the method is used for point cloud synthesis, the synthesis speed is fast and the synthesis accuracy is high. The resulting image is sharp and full without ghosting.

Description of drawings

Fig. 1 is a schematic structural diagram of a reference body used for acquiring 3D point cloud data in the present invention.

Fig. 2 is another schematic structural diagram of the reference body used for acquiring 3D point cloud data in the present invention.

Fig. 3 is a schematic flow chart of the point cloud synthesis method in the present invention.

Figure 4 is a point cloud image of rapeseed without reference body synthesis.

Fig. 5 is a point cloud image of rapeseed synthesized by reference body.

Detailed ways

Example 1

As shown in Figure 1, a reference body for three-dimensional point cloud data acquisition includes a base 1, a support shaft 2 perpendicular to the base 1 is fixed in the center of the base 1, and two solid spheres 3 placed up and down are arranged on the support shaft 2 , the two spheres 3 are fixedly connected through the connecting shaft 4;

The surface of the sphere 3 has a sandblasting layer, and the spherical profile of the sphere 3 after the sandblasting treatment is 0.05, and the surface roughness is 3.2;

The material of the sphere 3 must be metal, so that the present invention can obtain a higher degree of spherical profile with a lower processing cost. In this embodiment, the material of the sphere 3 is selected from bearing steel, and other metals such as iron alloy and cast iron can also be selected according to actual needs. etc., as long as the processing accuracy of the shape of the ball 3 can be guaranteed; it is also possible to directly purchase high-precision bearing steel balls from the market, and then sandblast and weld them by yourself;

The diameter of the sphere 3 is related to the direct size of the object to be measured. Since the diameter of the object to be measured in the present invention ranges from 1 to 60 cm, the diameter of the sphere 3 of the reference body is 40 to 50 mm, so that the scanned three-dimensional point cloud data In , there are enough spherical points.

As shown in Figure 3, a method for point cloud synthesis using a double-sphere reference body mainly includes the following steps:

(1) Place the double-sphere reference body on a turntable that can precisely control the rotation angle. The accuracy of the turntable is 0.000125 degrees, and scan the reference body with a three-dimensional structured light scanner;

(2) The turntable scans once every 90 degrees to obtain a point cloud at an angle of the spherical surface, that is, a local spherical point cloud. Four sets of local spherical point clouds located at the upper and lower two groups of squares with a total of 8 vertices are obtained by accumulative scanning four times, and calculated the central shaft of the turntable;

(3) Place the object to be tested on a turntable that can precisely control the rotation angle, and scan the object to be tested with a three-dimensional structured light scanner. The turntable scans once every time it rotates, and the rotation angle of the turntable can be adjusted according to different objects to be tested. Scan to get several 3D point cloud data;

(4) Using the central axis of rotation of the turntable calculated in step (2), the three-dimensional point cloud data scanned in step (3) is spliced to synthesize a complete three-dimensional point cloud;

Wherein, the calculation method of the central rotating shaft of the turntable in step (2) is as follows:

1) According to the local spherical point cloud of each scan, the center of each sphere is calculated. Each scan can obtain the upper and lower two sphere centers, and four scans can obtain the upper and lower two sets of four sphere centers located at the four vertices of a square;

2) Connect the center of the upper sphere of the reference body located at the diagonal of the square to obtain two intersecting diagonal lines;

3) Connect the center of the lower sphere of the reference body located at the diagonal of the square to obtain two intersecting diagonal lines;

4) Calculate the intersection points A(x _a , y _a , z _a ) and B(x _b , y _b , z _b ) of the upper and lower pairs of intersecting diagonals;

5) Connect point A and point B to obtain the central axis of rotation of the turntable.

Among them, the "synthesis of a complete three-dimensional point cloud" in step (4) refers to the calculation of pointing rotation around a fixed axis. The algorithm can be used in the book "Computer Graphics" by Sun Jiaguang and Yang Changgui (Tsinghua University Press, second edition in May 1995) , ISBN 7-302-01708-5/TP.746, the algorithm proposed in P346-348), as follows:

Let the axis coordinates be AB, A(x _a , y _a , z _a ), B(x _b , y _b , z _b );

Point cloud synthesis is the calculation of point rotation around a fixed axis. Assume that P ₁ is the result of the first scan, and P ₂ is the point cloud rotated by θ°. If you want to synthesize the point cloud of P ₂ into the coordinate system where P ₁ is located, it is equivalent to turning P ₂ (x _p , y _p , z _p ) around the axis AB by -θ° to P ₂ ^* (x _p ^* , y _p ^* , z _p ^* ), ie

[x _p ^* y _p ^* z _p ^* 1]＝[x _p y _p z _p 1]×R _ab

According to the difference between the coordinates of any two points in space is the direction number of the straight line connecting these two points, then the direction number of AB is: (a, b, c); where a=x _b -x _a , b=y _b -y _a , c=z _b -z _a ;

make: $v=\sqrt{a^2+b^2},$

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ <span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}& <span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}& <span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ {\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}& {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}& {\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]$

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; v</span>}& \mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; v</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; v</span>}& \mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; v</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; v</span>}& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; v</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; v</span>}& \mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; v</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]$

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; v</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; a</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; a</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; v</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; v</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; a</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; a</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; v</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; ;</span>$

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}& \mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; ;</span>$

but $R_{\mathrm{ab}}=T_A{R}_x{R}_{\mathrm{the\; y}}{R}_z{R}_{\mathrm{the\; y}}^{-1}{R}_x^{-1}{T}_A^{-1}.$

Example 2

In addition to the structure of the double-sphere reference body described in Embodiment 1, the reference body used for acquiring 3D point cloud data in the present invention can also be another structural device.

As shown in Figure 2, a reference body for three-dimensional point cloud data acquisition includes a base 1, a support shaft 2 perpendicular to the base 1 is fixed in the center of the base 1, and three solid spheres 3 placed up and down are arranged on the support shaft 2 , the sphere 3 and the sphere 3 are fixedly connected by the connecting shaft 4; according to actual needs, the number of the sphere 3 can be three or more than three;

The spherical profile, surface roughness, diameter and the selected material of the sphere 3 are all the same as in Embodiment 1.

As shown in Figure 3, the method for point cloud synthesis using a three-sphere reference body is the same as in Example 1; the difference is that the algorithm involved in Example 2 is different from Example 1:

① When using the three-sphere reference body for point cloud synthesis, by calculating the central axis of rotation of the turntable in step (2), multiple points on the central axis of rotation can be obtained. At this time, the calculation from multiple points to the axis of rotation is equivalent to a straight line of points in a limited three-dimensional space Fitting calculation, the algorithm can adopt the algorithm proposed by Xi Yang in the document "A method for fitting straight lines in space" (Journal of Qiqihar University, 2009, 25 (2): 64-67), and the specific algorithm is as follows:

For a series of spatial points: P _i (x _i , y _i , z _i ), i=1, . . . , m; solve the following equations:

FF'A=FX,

FF'B=FY,

in:

$\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; =</span>\begin{array}{cccc}{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}& {\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}& <span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span>& {\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}\\ \mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}& <span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span>& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}<span\; class="notranslate">\; ;</span>$

A=[a b]'; X=[x ₁ ... x _m ]';

B=[c d]'; Y=[y ₁ ...y _m ]'

According to m sets of data points, the values of a, b, c, and d can be obtained by solving the equations. When a, b, c, d are obtained, the linear equation of the space is obtained:

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; az</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; b</span>}\\ \mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; cz</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; d</span>}\end{array}\right.$

② The three-sphere reference body performs the calculation of "synthesizing a complete 3D point cloud" in step (4), and the specific algorithm is as follows:

Take any two points A'B' on the straight line obtained in the previous step, where A'(x' _a , y' _a , z' _a ), B'(x' _b , y' _b , z' _b ) ;

Point cloud synthesis is the calculation of point rotation around a fixed axis. Assume that P ₁ is the result of the first scan, and P ₂ is the point cloud rotated by θ°. If you want to synthesize the point cloud of P ₂ into the coordinate system where P ₁ is located, it is equivalent to turning P ₂ (x _p , y _p , z _p ) around the axis AB by -θ° to P ₂ ^* (x _p ^* , y _p ^* , z _p ^* ), ie

[x _p ^* y _p ^* z _p ^* 1]＝[x _p y _p z _p 1]×R _ab

According to the difference between the coordinates of any two points in space is the direction number of the straight line connecting the two points, then the direction number of AB is: (a', b', c'); where a'=x' _b -x' _a , b'=y' _b -y' _a , c'=z' _b -z'_a;

make: $v^{,}=\sqrt{a^{\&prime;2}+b^{\&prime;2}},$

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ <span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& <span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& <span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ {\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& {\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]$

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& {\mathrm{<span\; class="notranslate">\; c</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; v</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& {\mathrm{<span\; class="notranslate">\; b</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; v</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& <span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; b</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; v</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& {\mathrm{<span\; class="notranslate">\; c</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; v</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& {\mathrm{<span\; class="notranslate">\; c</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; v</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& <span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; b</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; v</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& {\mathrm{<span\; class="notranslate">\; b</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; v</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& {\mathrm{<span\; class="notranslate">\; c</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; v</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]$

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}{\mathrm{<span\; class="notranslate">\; v</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; a</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ <span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& {\mathrm{<span\; class="notranslate">\; v</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; ;</span>$ ${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}{\mathrm{<span\; class="notranslate">\; v</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& <span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ {\mathrm{<span\; class="notranslate">\; a</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& {\mathrm{<span\; class="notranslate">\; v</span>}}^{<span\; class="notranslate">\; \&prime;</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; ;</span>$

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}& \mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; ;</span>$

but $R_{\mathrm{ab}}=T_A{R}_x{R}_{\mathrm{the\; y}}{R}_z{R}_{\mathrm{the\; y}}^{-1}{R}_x^{-1}{T}_A^{-1}.$

Combining Embodiment 1 and Embodiment 2, the following is a comparison of the image effects of point cloud synthesis without using a reference body and using a reference body:

As shown in Figure 4, when the reference body is not used, the reference point is only selected with the naked eye and the mouse operation, and then the image synthesis of the rapeseed point cloud is performed; in the figure, it can be clearly seen that some interrupted petioles due to splicing errors, etc. .

As shown in Figure 5, when the reference body is used, and the data obtained from the rapeseed point cloud in Figure 4 are the same set of data, then the image synthesis of the rapeseed point cloud is performed; The petioles are relatively smooth, consistent and complete.

Conclusion: When the reference point method is used for point cloud synthesis in Figure 4, the synthesis time is about half an hour, and the result of manual selection of reference points is very unstable, and repeated debugging is required according to the synthesis results, similar to the trial and error method; Figure 5 uses this The invented method uses the reference body to measure the center rotation axis and then synthesizes the point cloud. The synthesis speed is as fast as 2 minutes, and the synthesized image is clear and complete without ghosting.

Claims (6)

1. A reference body for three-dimensional point cloud data acquisition, comprising a base, characterized in that, the center of the base is fixed with a support shaft perpendicular to the base, and the support shaft is provided with at least two metal spheres placed up and down, The spheres are fixedly connected by a connecting shaft; the surface of the spheres has a sandblasting layer; the spherical profile of the spheres is 0.05, and the surface roughness is 3.2-6.3. 2. The reference body for acquiring 3D point cloud data according to claim 1, wherein the material of the sphere is selected from one of bearing steel, iron alloy, and cast iron. 3. The reference body for acquiring three-dimensional point cloud data according to claim 1, wherein the number of said spheres is two. 4. The reference body for acquiring 3D point cloud data according to claim 1, wherein the number of said spheres is three or more. 5. A point cloud synthesis method, is characterized in that, comprises the steps: (1) Place the reference body as described in claim 3 on a turntable that can precisely control the rotation angle, and scan the reference body with a three-dimensional structured light scanner; (2) The turntable scans once every 90 degrees to obtain a point cloud at an angle of the spherical surface, that is, a local spherical point cloud. Four sets of local spherical point clouds located at the upper and lower two groups of squares with a total of 8 vertices are obtained by accumulative scanning four times, and calculated the central shaft of the turntable; (3) Place the object to be tested on a turntable that can precisely control the rotation angle, and scan the object to be tested with a three-dimensional structured light scanner. The turntable scans once every time it rotates, and the rotation angle of the turntable can be adjusted according to different objects to be tested. Scan to get several 3D point cloud data; (4) Using the central axis of rotation of the turntable calculated in step (2), the 3D point cloud data scanned in step (3) is used to splice the 3D point cloud data to synthesize a complete 3D point cloud. 6. point cloud synthesis method according to claim 5, is characterized in that, the central axis of rotation calculation method of turntable in described step (2) is as follows: 1) According to the local spherical point cloud of each scan, the center of each sphere is calculated. Each scan can obtain the upper and lower two sphere centers, and four scans can obtain the upper and lower two sets of four sphere centers located at the four vertices of a square; 2) Connect the center of the upper sphere of the reference body located at the diagonal of the square to obtain two intersecting diagonal lines; 3) Connect the center of the lower sphere of the reference body located at the diagonal of the square to obtain two intersecting diagonal lines; 4) Calculate the intersection points A(x _a , y _a , z _a ) and B(x _b , y _b , z _b ) of the upper and lower pairs of intersecting diagonals; 5) Connect point A and point B to obtain the central axis of rotation of the turntable.

Images