CN109490251A - Underwater refractive index self-calibrating method based on light field multilayer refraction model - Google Patents
Underwater refractive index self-calibrating method based on light field multilayer refraction model Download PDFInfo
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- CN109490251A CN109490251A CN201811254277.1A CN201811254277A CN109490251A CN 109490251 A CN109490251 A CN 109490251A CN 201811254277 A CN201811254277 A CN 201811254277A CN 109490251 A CN109490251 A CN 109490251A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
Abstract
The present invention proposes a kind of underwater refractive index self-calibrating method based on light field multilayer refraction model.Under water in shooting environmental, imaging ray passes sequentially through these three media of water, glass, air.In known camera internal reference, in the case where the refractive index of air and glass, thickness and stereo visual system relative attitude, the present invention is by shooting one group of clearly scaling board picture in measurement sea area, according to object point P this constraint on the straight line that left and right two constraint plane of camera (plane that interface normal and incident ray determine) is intersected, to measure shooting sea area refraction index of sea water μ.Underwater refractive index self-calibrating method disclosed by the invention based on light field multilayer refraction model can be widely applied in High Precision Underwater ranging and underwater 3 D reconstruction.
Description
Technical field
The present invention relates to underwater calibration technique field more particularly to a kind of underwater refractions based on light field multilayer refraction model
Rate self-calibrating method.
Background technique
The refractive index of water is for undersea ranging, three-dimensional reconstruction important in inhibiting.Underwater refractive index with the raising of temperature and
Reduce, increases with the increase of salinity.It fathoms for one as the instrument of 2-3m, when variations in refractive index one thousandth, then
Error just reaches 3mm at 3m.Therefore, high-precision underwater refractive index calibration is an important scientific issues.
There are many kinds of the methods for measuring refractive index, and Song Shixia et al. " surveys the refraction of water with Michael's interferometer in its paper
2015 (21): the Shandong rate [J] industrial technology proposes a kind of index glass by measuring Michelson's interferometer in 255-255. "
The method of amount of movement and its corresponding interference fringe variation number and then measurement water refractive index in water；Li Qiang et al. is in its paper
" refractive index [J] optical precision engineering of capillary imaging method accurate measuring trace quantity liquid, 2012,20 (7): 1440-1446. "
In cylindrical lens are constituted with the capillary for being filled with transparency liquid, the image-forming principle based on Coaxial Spherical Optical System, to optical imagery
The magnifying power of system carries out the measurement of single parameter, and then calculates the refractive index of testing liquid.
Although it is above-mentioned these be used for measure refractive index method precision it is higher, its experimental provision build it is all more complicated,
Equipment is expensive, to the measurement that the professional tool of operator there are certain requirements and be only applicable under laboratory environment, is applying to
When underwater or even deep-marine-environment measures, actual operation is relatively low.
Summary of the invention
In view of the defects existing in the prior art, the purpose of the present invention is to provide a kind of based on light field multilayer refraction model
Underwater refractive index self-calibrating method.
For this purpose, the present invention adopts the following technical scheme:
Under water in shooting environmental, imaging ray passes sequentially through these three media of water, glass, air.In known camera
Ginseng, in the case where the refractive index of air and glass, thickness and stereo visual system relative attitude, by being shot in measurement sea area
One group of clearly scaling board picture, according to object point P, in left and right two constraint plane of camera, (interface normal and incident ray are determined
Plane) this constraint on the straight line that is intersected, to measure shooting sea area refraction index of sea water μ.
A kind of underwater refractive index self-calibrating method based on light field multilayer refraction three-dimensional model, operating procedure are as follows:
Step 1: on the clear scaling board picture that left and right camera is clapped, extraction obtains corresponding one group of picture point, left
Picture point ml, right picture point mr；
Step 2: it according to the light field representation method of light, calculates separately and left and right camera picture point is passed by multilayer interface
The incident ray in water is reached after broadcasting and reflectingAnd it is converted into light field vectorql,qr；
Step 3: vector sum point under right camera coordinates system is transformed into left camera coordinates system:qr'=
Rl_r×qr+tl_r, the z-axis of right multilayer refraction coordinate system is similarly obtained: zr'=Rl_r×zr, or'=tl_r；
Step 4: it is constrained according to plane normal and point, finds out left and right camera constraint plane π respectivelyl、πr；Left camera constraint
Plane is expressed as: plane normalA point o in planel=[0 0 0]；Right camera constraint plane indicates are as follows: planar process
LineA point o in planer'=tl_r；
Step 5: two constraint planes intersect at straight line, are known by the law of refraction, and object point P is on this line；
Step 6: estimating the refractive index of seawater between 1.3 to 1.5, is determined and is rolled within this range using search method
Penetrate rate；Take the interior a certain refractive index μ in index regioni, the light after the corresponding the last layer medium refraction of left and right camera picture point at this time
Straight line in line and step 5 intersects at two o'clock respectively, and when this distance between two points minimum, corresponding μ is the folding of seawater
Penetrate rate.
Compared with prior art, the present invention have following obvious prominent substantive distinguishing features and significant technology into
Step:
1, stated accuracy is high, is carried out using the underwater stereoscopic vision system calibration method based on multilayer refraction model to camera
Calibration, it is more much higher than traditional national forest park in Xiaokeng stated accuracy, systematic error is not present.
2, easy to operate, it is not required to carry out the multiposition calibration in viewing field of camera under water, it only need to be in measurement waters shooting one
Secondary scaling board can determine measurement waters refractive index.
3, imaging process is described using the method that light field converts.Light field is not only wrapped compared to traditional light vector
It also include location information containing directional information.The propagation of light field is directly indicated with the mode of linear transformation with refraction so that light
The process of propagation is more intuitive.
Detailed description of the invention
Fig. 1 is that light field provided in an embodiment of the present invention describes schematic diagram.
Fig. 2 is the light field multilayer plane of refraction system model that the embodiment of the present invention is used.
Fig. 3 is that the embodiment of the present invention demarcates underwater refractive index flow chart.
Specific embodiment
The present invention is described in detail with reference to the accompanying drawings and examples.
As shown in Figure 1, carrying out related description to light field first.Light pass through two parallel planes, hand over respectively two planes in
Point o and od.The distance between two parallel planes are d=1, and oo' is perpendicular to two planes.Point o in first plane is indicated
For [u, v]T, vector o'odIt is expressed as [s, t]T, so light oodPropagate in space can with four-dimensional light field function [u, v, s,
t]TIt indicates.The location information (u, v) for first plane record light that light passes throughT, the direction of second plane record light
Information (s, t)T。
As shown in Fig. 2, being based on light field representation method, multilayer refraction three-dimensional model is established, demarcates the refraction ginseng of two cameras
Number, operating procedure are as follows:
Step 1: carrying out one camera calibration to left camera and right camera in air respectively, obtains the intrinsic parameter of one camera
Camera matrix cameraMatrixL, cameraMatrixR and distortion factor distortionL, distortionR.Table 1 provides
Calibration result.
Camera calibration parameter in 1 air of table
Step 2: using " the underwater stereoscopic view based on multilayer refraction model in Chinese patent CN201710702222.1
Feel system calibrating method " camera is demarcated in pond, obtain the refraction parameter (n of two camerasL, dL, miuL)、(nR,
dR, miuR) and vertical extracorporeal parameter tl_r, Rl_r；
Camera is demarcated under water using light field multilayer refraction model in above-mentioned steps two, comprising the following steps:
Step is 1.: the gridiron pattern scaling board in shooting pond.Arbitrarily selected 8 positions shoot picture between 1m -2m,
Picture is located substantially at middle position in two viewing field of camera, and scaling board tilt angle can not be too big, it is ensured that the picture clapped
Angle point is clear.
Step is 2.: extracting the gridiron pattern picture angle point taken using Harris corner detection approach, uses what is demarcated in advance
One camera calibrating parameters cameraMatrixL, cameraMatrixR, distrotionL, distortionR angle steel joint coordinate is gone
Except distortion.
Step is 3.: selecting the initial value of parameter to be calibrated, follows the example of line initial value n=[0 0 1] and refractive index initial value miu=
[11.51.33] (refractive index for respectively representing air, glass and water), iterates to calculate out the refraction parameter (n of two camerasL, dL,
miuL)、(nR, dR, miuR) and outer parameter Rl_r, tl_r.Table 2 give calibration refraction parameter and vertical extracorporeal parameter.
2 underwater stereoscopic vision calibration parameter of table
As shown in figure 3, measurement shoots sea area refraction index of sea water μ on the basis of above-mentioned steps, operating procedure is as follows:
Step 1: on the clear scaling board picture that left and right camera is clapped, extraction obtains corresponding one group of picture point, left
Picture point ml, right picture point mr；
Step 2: it according to the light field representation method of light, calculates separately and left and right camera picture point is passed by multilayer interface
The incident ray in water is reached after broadcasting and reflectingAnd it is converted into light field vectorql,qr；
Step 3: vector sum point under right camera coordinates system is transformed into left camera coordinates system:qr'=
Rl_r×qr+tl_r, the z-axis of right multilayer refraction coordinate system is similarly obtained: zr'=Rl_r×zr, or'=tl_r；
Step 4: it is constrained according to plane normal and point, finds out left and right camera constraint plane π respectivelyl、πr；Left camera constraint
Plane is expressed as: plane normalA point o in planel=[0 0 0]；Right camera constraint plane indicates are as follows: plane
NormalA point o in planer'=tl_r；
Step 5: two constraint planes intersect at straight line, are known by the law of refraction, and object point P is on this line；
Step 6: estimating the refractive index of seawater between 1.3 to 1.5, is determined and is rolled within this range using search method
Penetrate rate；Take the interior a certain refractive index μ in index regioni, the light after the corresponding the last layer medium refraction of left and right camera picture point at this time
Straight line in line and step 5 intersects at two o'clock respectively, and when this distance between two points minimum, corresponding μ is the folding of seawater
Penetrate rate.
In long 4m, wide 2m takes the photograph one group of clear picture for having target, the refraction of measurement shooting waters water in the pond of high 1.2m
Rate is μ=1.3337.
Claims (1)
1. a kind of underwater refractive index self-calibrating method based on light field multilayer refraction model, in known camera internal reference, air and glass
It is clear by shooting one group in measurement sea area in the case where the refractive index of glass, thickness and stereo visual system relative attitude
Scaling board picture, according to object point P this constraint on the straight line that left and right two constraint plane of camera is intersected, to measure bat
Take the photograph sea area refraction index of sea water μ；Characterized by comprising the following steps:
Step 1: on the clear scaling board picture that left and right camera is clapped, extraction obtains corresponding one group of picture point, left picture point
ml, right picture point mr；
Step 2: according to the light field representation method of light, calculate separately for left and right camera picture point by multilayer interface propagate and
The incident ray in water is reached after refractionAnd it is converted into light field vectorql,qr；
Step 3: vector sum point under right camera coordinates system is transformed into left camera coordinates system:qr'=Rl_r×qr
+tl_r, the z-axis of right multilayer refraction coordinate system is similarly obtained: zr'=Rl_r×zr, or'=tl_r；
Step 4: it is constrained according to plane normal and point, finds out left and right camera constraint plane π respectivelyl、πr；Left camera constraint plane
It indicates are as follows: plane normalA point o in planel=[000]；Right camera constraint plane indicates are as follows: plane normalA point o in planer'=tl_r；
Step 5: two constraint planes intersect at straight line, are known by the law of refraction, and object point P is on this line；
Step 6: estimating the refractive index of seawater between 1.3 to 1.5, determines refractive index within this range using search method；
Take the interior a certain refractive index μ in index regioni, at this time the light after the corresponding the last layer medium refraction of left and right camera picture point with
Straight line in step 5 intersects at two o'clock respectively, and when this distance between two points minimum, corresponding μ is the refraction of seawater
Rate.
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| CN111750836A (en) * | 2020-06-10 | 2020-10-09 | 南京林业大学 | Multi-optical medium close-range photogrammetry method |
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