Polarization meridian plane-based three-dimensional real-time attitude determination method for polarization compassTechnical Field
The invention relates to the technical field of three-dimensional real-time attitude determination methods of polarization compasses, in particular to a three-dimensional real-time attitude determination method of a polarization compass based on a polarization meridian plane.
Background
As an autonomous navigation instrument applied to the earth atmosphere, the three-dimensional real-time attitude determination technology of the polarization compass is a key technology for continuously researching, exploring and seeking breakthrough in all countries of the world. The technology can solve the problem of real-time acquisition of the three-dimensional attitude information of the high-precision carrier under the condition of satellite navigation rejection or interference.
As a result of the analysis of paper "Limitation of Rayleigh sky model for bio-inspired polarized skylight navigation in three-dimensional attitude determination", polarization navigation is unable to achieve three-dimensional real-time pose determination when only a single solar vector is considered. In order to realize real-time attitude determination of the polarization compass, the existing autonomous navigation method of the polarization compass is mostly dependent on other devices such as a horizon, a magnetometer, a gravity pendulum, an inertial navigation system or an inclinometer to provide horizontal reference measurement information. Patent number CN110231025A is a dynamic orientation method and system based on strapdown polarized light compass, the pitch angle and roll angle of the polarized compass are obtained by strapdown inertial navigation, and then the course angle of the carrier is obtained by solving the polarized meridian. The patent number CN108917749A, a method for extracting solar meridian based on polarization imaging, obtains meridian in polarization compass imaging by a method for fitting and estimating the polarization meridian under the condition of horizontal placement, and further can calculate course angle. The article IntegratedPolarized Skylight Sensor andMIMUWith AMETRIC MAP forUrban GroundNavigation obtains the heading state of a polarization compass by means of a Miniature Inertial Measurement Unit (MIMU).
However, the introduction of an external horizontal reference instrument has the following effect on the polarization compass measurement system. Firstly, the error of a level measurement system of an external level measurement instrument (such as an inclinometer, inertial navigation and the like) becomes an important component for determining the polarization navigation precision, secondly, the installation calibration error of a level reference instrument and a polarization system is directly coupled in the polarization navigation system, and finally, the level reference instrument is realized based on an accelerometer, and is not suitable for a high-speed environment. Finally, the navigation accuracy and adaptability of the polarized navigation system are limited.
In view of the above, it is needed to break through the limitation of the external horizontal reference instrument on the autonomous navigation of the polarization compass, and realize the three-dimensional real-time autonomous attitude determination of the polarization compass independent of the external horizontal reference.
Disclosure of Invention
The invention aims to solve the problems that the realization of the existing polarization compass autonomous attitude determination technology needs to rely on an external instrument to provide horizontal reference information, and provides a polarization compass three-dimensional real-time attitude determination method based on a polarization meridian plane, which can realize high-precision polarization autonomous attitude determination under the condition of not relying on the external horizontal reference instrument.
The invention adopts the following technical scheme:
A three-dimensional real-time attitude determination method of a polarization compass based on a polarization meridian plane is characterized by comprising the following steps:
firstly, respectively extracting a sun polarization neutral point and a sun vector based on a sun polarization field imaging mode, and establishing a polarization meridian plane model;
Secondly, establishing a measurement model of the polarization meridian plane based on the conversion relation of the polarization meridian plane between a geographic coordinate system and a polarization coordinate system;
And thirdly, based on the polarization meridian plane measurement model, a simultaneous sun vector coordinate system conversion model is used for calculating real-time attitude information of the polarization compass, namely a course angle, a pitch angle and a roll angle.
As a preferred technical scheme of the present invention, in the first step, based on a solar polarization field imaging mode, a solar polarization neutral point and a solar vector are respectively extracted, and a polarization meridian plane model is established, and the implementation steps are as follows:
(a1) Sunlight interacts with atmospheric molecules or aerosol particles in the earth atmosphere to generate polarization, and a polarization compass is utilized to image and analyze polarization of an atmosphere polarization field, so that polarization degrees and polarization vectors corresponding to different observation directions in the observation moment are obtained;
(a2) Calculating the polarization degree and the polarization direction corresponding to different coordinates in the polarization imaging based on a Stirling vector formula, so as to obtain a polarization degree image and a polarization direction image of polarization compass polarization detection;
(a3) Based on the polarization degree image, a neutral point region (minimum polarization degree region) is obtained by using a polarization degree threshold segmentation method, and then a polarization neutral point coordinate Ne (xNE,yNE) and a neutral point vector Ne under a polarization compass coordinate system are calculated by using a K-means clustering and a polarization degree gravity center method;
(a4) Based on the polarization direction image, a sun vector optimization solving model is established according to the principle that the polarization vector and the sun vector are mutually perpendicular to obtain an optimal sun vector (SB)＝[xb,yb,zb]＝argmin(SBTEETSB), wherein SB is the sun vector under a polarization compass coordinate system, E is the polarization E vector under the polarization compass coordinate system, and SBT and ET represent the transposition of the vectors;
(a5) Based on the neutral point vector Ne and the sun vector SB, a polarization meridian plane under a polarization compass coordinate system corresponding to the observation time, namely Y, is established
As a preferred technical scheme of the present invention, in the second step, a measurement model of the polarization meridian plane is established based on the conversion relation between the geographic coordinate system and the polarization coordinate system of the polarization meridian plane, and the implementation steps are as follows:
(b1) Based on the observation time t and the observation position information, calculating a reference solar vector SN of a solar vector under the east-north-heaven of a geographic coordinate system, namely an altitude angle hS and an azimuth angle of the solar vector SN, from solar ephemeris
(B2) In the geographical coordinate system, the N-system, the polarization meridian plane is expressed as
(B3) Polarization meridian plane based on B-system under polarization coordinate system obtained in the first stepEstablishing conversion models between an N-system and a B-system respectively: wherein R2、R1 and R3 are rotation matrices around Y-axis, X-axis and Z-axis respectively, pitch angle θX, roll angle θY and heading angle,Is a transformation matrix between a polarization compass coordinate system B-system and a geographic coordinate system N-system.
In the third step, based on the polarization meridian plane measurement model and the simultaneous solar vector coordinate system conversion model, the real-time attitude information of the polarization compass, namely the pitch angle thetaX, the roll angle thetaY and the heading angle phi, is calculated, and the implementation steps are as follows:
(c1) Based on the reference solar vector SN＝[xn,yn,zn in the second step and the observed solar vector SB＝[xb,yb,zb in the first step, a standard conversion model is established:
(c2) According to the measurement model of the polarization meridian plane obtained by solving in the second step, a simultaneous solar vector coordinate system conversion model is obtained:
(c3) And solving the above to obtain the three-axis attitude angles of the polarization compass, namely a pitch angle thetaX, a roll angle thetaY and a course angle phi.
Compared with the prior art, the invention has the advantages that:
(1) The defects of the prior art are mainly that the prior art relies on an external instrument to provide horizontal reference information, so that the navigation precision and adaptability of polarization autonomous attitude determination are limited. Firstly, the error of a horizontal measurement system of an external horizontal measurement instrument (such as an inclinometer and inertial navigation) becomes an important component for determining the polarization navigation precision, secondly, the installation calibration error of a horizontal reference instrument and a polarization system is directly coupled in the polarization navigation system, and finally, the horizontal reference instrument is mostly realized based on an accelerometer and is not suitable for a high-speed environment.
(2) Compared with the defects in the prior art, the method solves the problem that three-dimensional real-time attitude determination cannot be realized when only a single solar vector is considered in polarization navigation, and the realization of the method does not depend on an external instrument to provide horizontal reference information;
(3) Compared with the defects of the prior art, the method has the advantages that the requirement that the symmetrical characteristic of the orientation method based on the polarization meridian needs to be horizontally placed is overcome, and the method is also suitable in an inclined state;
(4) All the advantages of the invention are that the invention proposes to represent the propagation process of the incident polarized light by the polarized meridian plane, and expand the two-dimensional characteristic sun vector into the three-dimensional characteristic polarized meridian plane, thereby realizing the autonomous attitude determination of the polarized compass without an external horizontal reference instrument.
Drawings
FIG. 1 is a flow chart of a design of a three-dimensional real-time attitude determination method of a polarization compass based on a polarization meridian plane;
FIG. 2 is a polarization degree image of a polarization compass of the present invention;
FIG. 3 shows the neutral point region extraction results after K-means clustering and polarization degree gravity center method.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings and examples.
As shown in fig. 1, 2 and 3, the invention discloses a three-dimensional real-time attitude determination method of a polarization compass based on a polarization meridian plane. The method characterizes the propagation process of incident polarized light rays by using a polarization meridian plane, and expands a two-dimensional characteristic solar vector into a three-dimensional characteristic polarization meridian plane.
Sunlight interacts with atmospheric molecules or aerosol particles in the earth atmosphere to generate polarization, and the polarization compass is utilized to image and analyze polarization of an atmosphere polarization field, so that the polarization degree DOP and the polarization direction AOP corresponding to different observation directions in the observation moment are obtained:
Wherein S0、S1 and S2 are known polarization directions, and are calculated from imaging gray values I (0 °), I (45 °), I (90 °) and I (135 °) corresponding to 0 °, 45 °, 90 ° and 135 °, respectively:
S1=I(0°)-I(90°)
S2=I(45°)-I(135°)
each 4 polarization-analysis-direction pixels constitute one polarization degree pixel, so that for a polarization image with a resolution of n×n, the polarization degree image thereof is dop=d (N/2 ), and then, a neutral point is obtained according to the polarization degree.
First, a polarization degree threshold value is set as DOPTH, and thus a polarization degree image is divided to obtain a neutral point region:
and classifying the polarization degree point diagram after threshold segmentation by using a K-means clustering method. For example, the polarization degree binary image is divided into 3 parts. Then, the most 2 clustering results are selected as neutral point region candidates, and the result is denoted as Ni (x, y). Where i is the number of cluster regions and (x, y) is the pixel coordinates.
The Euclidean distance between the center of the clustering area and each pixel is calculated, and secondary screening is carried out by 2/3 of the maximum Euclidean distance:
Where (xc,yc) is the cluster center of the ith neutral point cluster region.
Using the polarization degree gravity center method, the polarization neutral point coordinates Ne (xNE,yNE) are calculated from the neutral point region:
Where D (x, y) is the degree of polarization of the (x, y) pixel at the coordinates in the neutral point region.
In the polarization compass imaging coordinate system, the polarization neutral point vector Ne:
Ne=[xNE-x0,yNE-y0,-f]
where (x0,y0) is the principal point of the polarization compass imaging and f is the focal length.
Meanwhile, E-vector E sets of different observation directions under a polarized compass coordinate system can be obtained from the polarized directions AOP, and E= [ E1,e2,...,em ]. Based on the principle that the polarization vector and the sun vector are perpendicular to each other, a sun vector optimization solution model is established, and an optimal sun vector SB under a polarization compass coordinate system is obtained:
(SB)＝[xb,yb,zb]＝argmin(SBTEETSB)
Where SB is the sun vector in the polarized compass coordinate system, E is the polarized E vector in the polarized compass coordinate system, and SBT and ET represent the transpose of the vectors.
In the B-system under the polarization coordinate system, based on the neutral point vector Ne and the solar vector SB, a polarization meridian plane corresponding to the observation time is established, namely
In the N-system of the geographic coordinate system, the polarization meridian plane consists of a solar vector and a zenith direction, namely
Where SN is the direction vector of the solar vector under the N-system.
Based on the observation time t and the longitude and latitude of the observation position information, SN is obtained by solar ephemeris calculation:
Wherein hS is equal toThe altitude and azimuth of the solar vector SN, respectively.
From the N-system to the B-system, the polarization meridian plane coordinate system conversion can be expressed as:
wherein R2、R1 and R3 are rotation matrices around Y-axis, X-axis and Z-axis respectively, pitch angle θX, roll angle θY and heading angle,Is a transformation matrix between a polarization compass coordinate system B-system and a geographic coordinate system N-system.
The polarization meridian plane can be expressed by its normal vector, and thus has
Wherein FYB and FYN are respectively polarization meridian planesAnd (3) withIs a unit normal vector of (a).
On the other hand, in the polarization compass observation system, the coordinate system conversion relationship between the sun vector SB in the polarization observation coordinate system and the reference sun vector SN in the geographic coordinate system is observed as follows:
because the above formula lacks a measurement relation, the measurement model of the polarization meridian plane according to the present invention can complement the measurement relation, so that there are:
And obtaining the three-axis attitude angle of the polarization compass based on the above calculation, wherein the three-axis attitude angle is a pitch angle thetaX, a roll angle thetaY and a course angle phi.
What is not described in detail in the present specification belongs to the prior art known to those skilled in the art.