CN112022408A - Method for obtaining human dental arch curve based on binocular vision - Google Patents
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Abstract
The invention discloses a method for obtaining a human dental arch curve based on binocular vision, which belongs to the technical field of obtaining dental arch curves and comprises a binocular stereo camera and a laser point light source, wherein the binocular stereo camera comprises a left camera and a right camera; the dental arch curve obtained by the invention provides possibility for dynamically formulating the dental arch scanning track, and can be introduced into the software and hardware design of dental panoramic equipment.
Description
Technical Field
The invention relates to the technical field, in particular to a method for obtaining a human dental arch curve based on binocular vision.
Background
The dental panoramic imaging device is a medical device which scans a virtual dental arch curve through an X-ray beam and an X-ray detector to obtain a multi-frame image and generates a dental panoramic image by combining position and orientation information; the existing dental panoramic imaging device can preset dental arch curves for scanning and generating panoramic images. The patent of the pramipexole publication states that it can generate multiple tomographic layers and also construct and display dental arch images or partial images viewed from different directions. U.S. patent US 20150139524Al issued to vantech states that its dental panoramic imaging apparatus can automatically fuse multiple tomographic layers to produce the clearest panoramic image. This makes the preset arch curve different from the real arch curve even though the difference may affect the applicability in some cases, for example, the arches of adults and children are too different to share the same arch curve, and different arch curves need to be selected for scanning. The patent of the generation method of the dental arch line [ CN 106204688B ] [ CN 110211200A ] is published by Feisen science and Anke, and the method for acquiring the dental arch curve by using the dental CT three-dimensional tomography image is claimed, and a dental panoramic image is further generated. Although all the methods can obtain dental arch curves, the problems caused by individual differences of dental arches are solved. However, these methods bypass the dental panoramic imaging apparatus and also lose the advantages of the dental panoramic imaging apparatus: short imaging time, low radiation dose, no metal artifact and the like.
Disclosure of Invention
The invention aims to provide a method for obtaining a human dental arch curve based on binocular vision so as to solve the problems in the prior art.
In order to achieve the purpose, the invention provides the following technical scheme: a method for obtaining human dental arch curves based on binocular vision is characterized by comprising the following steps: the method comprises the following steps:
s100: setting a scanning reference position, scanning N points on the visible area of the anterior teeth to the left side and the right side of the position by using the laser point light source as a center, and marking the N points as a scanning point set N, wherein each point in the scanning point set forms a light spot;
s200: the binocular stereo camera collects a left image and a right image which take the reference position as the center, and identifies the positions of light spots in the two images;
s300: setting the middle point position of the connecting line of the optical centers of the two cameras as a coordinate origin, setting the vector direction of the optical center of the left camera pointing to the optical center of the right camera as the x-axis direction, setting the optical axis direction of the cameras as the z-axis direction, setting the gravity direction as the y-axis direction, constructing a three-dimensional space, and calculating the position of the light spot in the three-dimensional space through a triangulation algorithm;
s400: adopting parabolic curve fitting to obtain a dental arch curve;
a device for realizing the method for obtaining the human dental arch curve based on the binocular vision is characterized in that a binocular stereo camera consisting of two cameras and a laser point light source arranged in the middle of the binocular stereo camera are added on the basis of the existing dental panoramic imaging device, in the specific implementation process, the laser point light source scans N points which are symmetrically and uniformly distributed on the left and right of a visible area of anterior teeth (the visible area refers to a tooth area exposed as far as possible after a patient opens a mouth), wherein N is more than or equal to 5 and is an odd number, then the binocular stereo camera collects the left image and the right image which take the connecting line of the optical centers of the two cameras as the midpoint position, and transmits the left image and the right image to a microcomputer (such as a raspberry pie) through a network to automatically identify the positions of light spots generated by the laser point light sources in the two images, the position of the light spots in a three-dimensional space is obtained by a, the arch curve is obtained by curve fitting, (where the curve fitting may be a parabolic fitting).
In the step S100, the scanning point set N is a point where the reference positions are symmetrically and uniformly distributed around the center, the reference position is a middle incisor fixing position, and half of the scanning point set N is denoted as m, then
The floor function has the function of taking the maximum integer not greater than N/2;
the relationship between N and m is: n is 2 × m +1, N is not less than 5 and is an odd number;
the floor function is used to take the largest integer not greater than N/2, or rounded down, keeping N2 m +1 between the integers N and m, and the scan points can be labeled (-m, -m +1, -m +2, …,0, …, m-2, m-1, m);
and taking N scanning points, wherein N is more than or equal to 5, which is beneficial to the successful construction of the subsequent dental arch curve.
In step S200, the binocular stereo camera includes two cameras, the two cameras are symmetrically distributed, a distance between the two cameras, that is, a base line distance, is set to B, and a focal length of the cameras is set to f.
The step S300 includes the steps of:
s310: marking the points of the laser point light source scanning anterior tooth area as all integers from-m to m, and sequentially positioning the points to the sampling point p on the dental arch from left to rightiI is any integer value from-m to m;
s320: the method comprises the steps of collecting a left image and a right image by taking a reference position as a center through a left camera and a right camera in a binocular stereo camera, sampling the same point in a scanning point set N in the two images as a sampling point, and marking as Ileft、Iright；
S330: setting the midpoint position of the connecting line of the optical centers of the two cameras as a coordinate origin, setting the vector direction of the optical center of the left camera pointing to the optical center of the right camera as the x-axis direction, setting the gravity direction as the y-axis direction, constructing a two-dimensional coordinate system, and calculating the positions of the sampling points in the two images in the step S320 in the two-dimensional coordinate system, wherein the positions are (u) and (u) respectivelyleft,vleft) And (u)right,vright)；
S340: the light spot formed by the points is scanned by a triangulation method, and the position p of the light spot in the three-dimensional space is calculatedi(xi,yi,zi) The calculation formula is as follows:
the binocular vision triangulation algorithm may employ a three-dimensional measurement technique based on the parallax principle.
B is base line distance, f is focal length, D is parallax, D ═ uleft-urightV points on the head-up space due to two identical camerasleftAnd vrightAre theoretically equal, i.e. v ═ vleft＝vright；
The same point in the scanning point set N in the two images is taken as a sampling point for sampling, the position of the sampling point in the two-dimensional coordinate system is solved, and the position of the sampling point in the three-dimensional coordinate system is calculated, so that the position of the sampling point can be more accurately positioned.
In step S400, the dental arch is fitted to the parabolic curve, and the equation is expressed as:
z＝a*x2+b
z is the coordinate of the light spot position on the z axis, x is the coordinate of the light spot position on the x axis, b is a constant which is fixed and unchangeable, the constant can be obtained by pre-measurement, a is a parabolic model parameter, and the value of a is calculated by a least square method:
the dental arch curve obtained by the invention provides possibility for dynamically formulating a dental arch scanning track, and if the dental arch curve is introduced into the design of dental panoramic equipment software and hardware, the dental arch curve formula can possibly replace the existing static scanning mode of the preset dental arch.
In the step S300: y coordinate value y in three-dimensional coordinatesiThe constraint conditions of (1) are: and setting the standard deviation of the y-direction coordinates of all the light spots to be smaller than a preset value sigma:
u is the mean value of the y-direction coordinates of all the light spots;
z coordinate direction value z in three-dimensional coordinates0The constraint conditions of (1) are: z is a radical of0The difference from b satisfies less than a preset value τ:
|z0-b|≤τ
τ is a preset value constant, z0Is a z coordinate direction value;
the error value of the preset y-direction coordinate is smaller than the preset value sigma, and the error value of the z-direction numerical coordinate is smaller than the preset value tau, so that the accuracy is improved in the actual implementation process.
The device for obtaining the human dental arch curve based on the binocular vision is suitable for any one of claims 1 to 6, and is formed by adding a binocular stereo camera consisting of two cameras and a laser point light source on the basis of the existing dental panoramic imaging device;
the measurement device requires calibration of the binocular cameras prior to use, which includes calibration of the intrinsic parameters of each camera itself and calibration of the extrinsic parameters used to determine the positional relationship between the two cameras. In the field of machine vision, a Zhangyingyou calibration method can be adopted for camera calibration, and compared with most of intraoral equipment, the invention does not need to contact the teeth of a patient in the scanning imaging process, and can carry out non-contact measurement by belonging to intraoral equipment with dental panoramic imaging equipment; the measurement time is short, only N points on the dental arch curve need to be scanned and collected, and the whole image collection and processing time can be finished in the second level; in addition, the light spot formed by irradiating the dental arch with laser is also in a visible light wave band, and the optical signal which can be detected by the binocular camera is also in the wave band generally.
The laser point light source is positioned in the middle of the binocular vision measuring device.
Compared with the prior art, the invention has the beneficial effects that:
the method of the invention can improve the existing dental panoramic imaging device, and solves the problem that the difference between the preset dental arch curve and the real dental arch curve affects the applicability; the invention can obtain the information of the dental arch curve in advance before the scanning of the dental panoramic equipment is implemented, and can find out the dental arch curve which is the closest to the preset dental arch curve of the patient to be examined according to the information without the subjective judgment and manual selection of actual operators, thereby reducing the manual intervention as much as possible or providing at least one reference; the invention obtains the prior information of the dental arch curve and provides possibility for dynamically formulating the scanning track of the dental arch, and if the prior information is introduced into the design of software and hardware of dental panoramic equipment, the prior static scanning mode of the preset dental arch can be replaced.
Drawings
FIG. 1 is a schematic view of a measurement procedure for obtaining human arch curves based on binocular vision according to the present invention;
FIG. 2 is a schematic structural diagram of a measurement method for obtaining human dental arch curves based on binocular vision according to the present invention;
FIG. 3 is a schematic view of a geometrical position relationship structure between a point to be observed and a binocular stereoscopic vision system for obtaining a human dental arch curve based on binocular vision.
Reference numbers in the figures: 1. a right camera; 2. a left camera; 3. a laser point light source; 4. a dental arch curve to be measured; 5. laser spot location.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The first embodiment is as follows: as shown in fig. 1-2, a method for obtaining human dental arch curve based on binocular vision is characterized in that:
assuming that there is no measurement error, i.e., the focal lengths f of the left and right cameras are 2 and the base line distance B is 6 in an ideal case, the length and width of the image in the image plane are both 10, and the intersection point of the optical axis and the image plane is at the midpoint of the two-dimensional image, i.e., (u)0,v0) Set the base point position P as (5,5)0The coordinate is (0, 0, 10), then the two-dimensional coordinate of the base point in the left image is (u) according to the geometric relationshipleft,vleft)＝(5.65), the base point is two-dimensional coordinate (u) in the right imageright,vright) The three-dimensional coordinates can be calculated by substituting the formula (4.4,5), wherein the parallax D is uleft-uright＝1.2，v＝(vleft+vright)/2＝5, x0＝(uleft-u0)*B/D-B/2＝0，
z0Where the constant B of the parameter in the parabolic model is the z component value at the base point position in this example, i.e. B is 10, it is assumed that 7 points on the dental arch curve need to be measured by the binocular vision system, i.e. N is 7, and N is 3, where it is assumed that when the value of a is 0.1, the parabolic model is substituted to obtain the theoretical three-dimensional coordinates of the 7 points as:
when i is-3, x is-2, y is 0, and z is 10.4;
when i is-2, x is-1.3333, y is 0, and z is 10.1778;
when i is-1, x is-0.6667, y is 0, and z is 10.0444;
when i is 0, x is 0, y is 0, and z is 10;
when i is 1, x is 0.6667, y is 0, and z is 10.0444;
when i is 2, x is 1.3333, y is 0, and z is 10.1778;
when i is 3, x is 2, y is 0, and z is 10.4;
in this case, without measurement error, a-0.1 can be calculated.
Example two:
in the case of errors, noise is added to simulate the measurement error, and assuming that the measurement error is a random number uniformly distributed over x, y, z from-0.05 to 0.05, the coordinates of seven points can be generated as:
when i is-3, x is-1.9898, y is-0.0271, and z is 10.3943;
when i is-2, x is-1.3570, y is 0.0413, and z is 10.1384;
when i is-1, x is-0.6513, y is-0.0348, and z is 10.0906;
when i is 0, x is 0.0189, y is 0.0326, and z is 9.9505;
when i is 1, x is 0.6915, y is 0.0038, and z is 10.0719;
when i is 2, x is 1.3284, y is 0.0496, and z is 10.2095;
when i is 3, x is 1.9584, y is 0.0422, and z is 10.4369;
a can be calculated to be 0.1055.
The working principle is as follows: firstly, calibrating a binocular stereo camera, including calibrating internal parameters and external parameters, adjusting the head position of a person before carrying out dental panoramic scanning, keeping a dental arch curve of the human body to be positioned on a horizontal plane as much as possible, keeping an auditory orbit line on the horizontal plane in the specific implementation process, and fixing middle incisors at the same position through a fixed fulcrum on a middle incisor occlusal jaw support, wherein the position is also the reference position of a laser point light source scanning tooth or the position of 0 mark; the scanning positions of N points in the anterior dental area of the dental arch curve are determined to be uniformly distributed as much as possible, the fixed positions of the central incisors are symmetrically distributed, for the formation and fitting of a subsequent curve, in the specific implementation process, the initial scanning position may only need to be manually determined, the scanning positions are ensured to be within the visual field ranges of a left camera and a right camera in a binocular stereo camera, two images are collected by the left camera and the right camera in the binocular stereo camera in the horizontal plane, namely the plane where the dental arch curve is located, the sampling points are sequentially positioned from left to right on the dental arch, then the sampling points are positioned by a triangular positioning method, the coordinates of each sampling point in a three-dimensional space are calculated, and finally, a parabolic curve fitting is adopted according to the three-dimensional coordinates of the N points to obtain the dental arch curve.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Claims (8)
1. A method for obtaining human dental arch curves based on binocular vision is characterized by comprising the following steps: the method comprises the following steps:
s100: setting a scanning reference position, scanning N points on the visible area of the anterior teeth to the left side and the right side of the position by using the laser point light source as a center, and marking the N points as a scanning point set N, wherein each point in the scanning point set forms a light spot;
s200: the binocular stereo camera collects a left image and a right image which take the reference position as the center, and identifies the positions of light spots in the two images;
s300: setting the middle point position of the connecting line of the optical centers of the two cameras as a coordinate origin, setting the vector direction of the optical center of the left camera pointing to the optical center of the right camera as the x-axis direction, setting the optical axis direction of the cameras as the z-axis direction, setting the gravity direction as the y-axis direction, constructing a three-dimensional space, and calculating the position of the light spot in the three-dimensional space through a triangulation algorithm;
s400: and (5) obtaining an arch curve by adopting parabolic curve fitting.
2. The method for obtaining human arch curves based on binocular vision according to claim 1, wherein: in the step S100, the scanning point set N is a point where the reference positions are symmetrically and uniformly distributed around the center, the reference position is a middle incisor fixing position, and half of the scanning point set N is denoted as m, then
The effect of the floor function is to take the largest integer no greater than N/2.
3. The method for obtaining human arch curves based on binocular vision according to claim 2, wherein: in step S200, the binocular stereo camera includes two cameras, the two cameras are symmetrically distributed, a distance between the two cameras, that is, a base line distance, is set to B, and a focal length of the cameras is set to f.
4. The method for obtaining human arch curves based on binocular vision according to claim 1, wherein: the step S300 includes the steps of:
s310: marking the points of the laser point light source scanning anterior tooth area as all integers from-m to m, and sequentially positioning the points to the sampling point p on the dental arch from left to rightiI is any integer value from-m to m;
s320: the method comprises the steps of collecting a left image and a right image by taking a reference position as a center through a left camera and a right camera in a binocular stereo camera, sampling the same point in a scanning point set N in the two images as a sampling point, and marking as Ileft、Iright；
S330: setting the midpoint position of the connecting line of the optical centers of the two cameras as a coordinate origin, setting the vector direction of the optical center of the left camera pointing to the optical center of the right camera as the x-axis direction, setting the gravity direction as the y-axis direction, constructing a two-dimensional coordinate system, and calculating the positions of the sampling points in the two images in the step S320 in the two-dimensional coordinate system, wherein the positions are (u) and (u) respectivelyleft，vleft) And (u)right，vright)；
S340: the light spot formed by the points is scanned by a triangulation method, and the position p of the light spot in the three-dimensional space is calculatedi(xi，yi，zi) The calculation formula is as follows:
b is base line distance, f is focal length, D is parallax, D ═ uleft-urightV points on the head-up space due to two identical camerasleftAnd vrightAre theoretically equal, i.e. v ═ vleft＝vright。
5. The method for obtaining human arch curves based on binocular vision according to claim 4, wherein: in step S400, the dental arch is fitted to the parabolic curve, and the equation is expressed as:
z＝a*x2+b
z is the coordinate of the light spot position on the z axis, x is the coordinate of the light spot position on the x axis, b is a constant which is fixed and unchangeable, the constant can be obtained by pre-measurement, a is a parabolic model parameter, and the value of a is calculated by a least square method:
6. The method for obtaining human arch curves based on binocular vision according to claim 1, wherein: in the step S300:
y coordinate value y in three-dimensional coordinatesiThe constraint conditions of (1) are: and setting the standard deviation of the y-direction coordinates of all the light spots to be smaller than a preset value sigma:
z coordinate in three-dimensional coordinates
Direction value z0The constraint conditions of (1) are: z is a radical of0The difference from b satisfies less than a preset value τ:
|z0-b|≤τ
τ is a preset value constant, z0Is the z coordinate direction value of the base point.
7. The binocular vision-based apparatus for obtaining human arch curves of the claim 1, wherein: the device adds a binocular stereo camera consisting of two cameras and a laser point light source on the basis of the existing dental panoramic imaging device, and executes the method for obtaining the human dental arch curve based on binocular vision as claimed in any one of claims 1 to 6.
8. The binocular vision-based apparatus for obtaining human arch curves of the claim 7, wherein: the laser point light source is positioned in the middle of the binocular vision measuring device.
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