CN117968669B - A method for determining heading based on the sky's significant light intensity area at the time of solar-lunar transition - Google Patents

Abstract

The invention provides a course determination method based on a sky significant light intensity region at alternate day and month, which belongs to the field of course determination and comprises the following steps: an optical sensor carrying a fisheye lens is adopted to obtain sky polarized light fields at alternate time of day and month, and filtering treatment is carried out on the light fields; selecting a significant light intensity region from the filtered light field information; considering the influence of the geometric characteristic and the pixels with larger light intensity of the area, and simultaneously, in order to avoid calculation errors caused by irregular geometric shapes and gray distribution, a square weighted gravity center method of gray is adopted to calculate the point on the celestial meridian, and the connecting line of the point and the center of the sky polarized light field is the celestial meridian; and combining the meridian position of the celestial body and the navigation solution model, and calculating to obtain the course angle of the horizontal carrier at the day-month alternation time. According to the invention, sky polarized light fields at alternate time of day and month are processed, and heading angle information of a celestial meridian and a horizontal carrier with high precision and strong robustness in the period is obtained.

Description

A method for determining heading based on the sky's significant light intensity area at the time of solar-lunar transition

Technical Field

The present invention belongs to the field of heading determination, and specifically relates to a heading determination method based on a significant light intensity area in the sky at the time of the transition between the sun and the moon. The method can realize high-precision and robust measurement of the celestial meridian based on sky light field information, thereby improving the heading angle calculation accuracy and robustness of the horizontal carrier at the time of the transition between the sun and the moon, and providing technical support for the all-day navigation application of a single optical sensor.

Background technique

Autonomous navigation technology is a core component to enhance the autonomous survival capability of moving vehicles and ensure the smooth implementation of missions. As a research frontier and important supplement in the field of autonomous navigation, autonomous navigation technology based on sky light field information measurement can effectively solve the problems of inertial navigation error accumulation over time and satellite navigation susceptibility to interference leading to signal loss, and is an effective way to achieve high-precision navigation under complex conditions.

Navigation by sensing the stable and orderly light field information in the sky is a bionic autonomous navigation technology. In nature, racing pigeons use the measurement of the sun's displacement and position to determine their current position angle change, thereby determining their position and flight direction. Insects such as moths rely on parallel light from stars or moonlight to fly in a straight line at a fixed angle.

Inspired by this, bionic navigation technology based on polarized light fields has developed rapidly and received widespread attention. Bionic autonomous navigation technology based on sky light field information has the characteristics of being passive, radiation-free, highly autonomous, and well concealed. Among them, navigation mechanisms based on celestial light fields and a variety of optical sensors have been extensively studied and well applied. Optical sensors such as sun/star sensors can obtain navigation information of spacecraft by sensing the light fields of celestial regions such as the sun. Polaris Corporation of the United States has designed SkyPASS, a polarization/star-sensitive combined navigation system that uses polarized light fields and celestial light fields. The system can be used for autonomous orientation in daytime satellite signal denial environments.

The transition between the sun and the moon mainly includes two time periods: dusk when the sun sets and the moon rises, and dawn when the moon sets and the sun rises. Compared with the daytime, the light field intensity in this time period is weaker and is more significantly affected by noise and weather interference. Compared with the night, the sky is affected by both the sun and the moon. The paper "Polarization transition between sunlit and moonlit skies with possible implications for animal orientation and viking navigation: anomalous celestial twilight polarization at partial moon" focuses on the analysis of the atmospheric light field changes in the two time periods of the transition between the sun and the moon at dusk and dawn. The study shows that the distribution of the atmospheric polarization light field is unstable during this period. Chinese patent CN115597586A (A heading angle extraction method based on the symmetry of the atmospheric polarization mode) proposes a method for calculating the heading of a carrier using the symmetric distribution law of the solar polarization light field. Chinese patent CN111595330A (A night polarization heading calculation method based on probability density function estimation) solves the heading angle according to the global light field statistical information of the moon, improving the heading angle accuracy of the horizontal carrier.

The above patents and papers have preliminarily explored the feasibility of navigation based on sky light field information. These studies perform navigation calculations based on daytime or nighttime light field information, or only raise the issue of unstable atmospheric light field information at the time of the sun and moon. Based on the above analysis, how to make full use of effective light field information for high-precision measurement and strong robust application at the time of the sun and moon is an important technical support for the all-day application of optical navigation equipment, especially at the time of the sun and moon, and is also an urgent problem to be solved.

Summary of the invention

In order to solve the above problems and overcome the shortcomings of the prior art, the present invention proposes a method for determining a heading based on a significant light intensity area in the sky at the time of the transition between the sun and the moon, which mainly includes: using an optical sensor equipped with a fisheye lens to obtain the polarized light field of the sky at the time of the transition between the sun and the moon, and filtering the light field; in the filtered light field information, selecting a significant light intensity area without processing edge stray light interference; taking into account the geometric characteristics of the area and the influence of pixels with larger light intensity, and in order to avoid calculation errors caused by irregular geometric shapes and grayscale distribution, the square weighted centroid method of grayscale is used to obtain a point on the celestial meridian, and the line connecting the point and the center of the polarized light field in the sky is the celestial meridian; combining the position of the celestial meridian and the navigation solution model, the heading angle of the horizontal carrier at the time of the transition between the sun and the moon can be calculated.

In order to achieve the above object, the present invention adopts the following technical scheme:

A method for determining a heading based on a sky region with significant light intensity at the time of the sun and moon transition comprises the following steps:

Step 1: Use an optical sensor equipped with a fisheye lens to obtain the polarized light field of the sky at the time of the sun and moon, and filter the light field to remove interference such as noise;

Step 2: In the filtered light field information, select a significant light intensity area according to the global light field distribution characteristics;

Step 3: In the area of significant light intensity, use the grayscale square weighted centroid method to find the point on the celestial meridian. The line connecting this point and the center of the sky polarized light field is the celestial meridian.

Step 4: Calculate the heading angle of the horizontal carrier at the time of the sun-moon transition by combining the celestial meridian position and the navigation solution model.

Compared with the prior art, the present invention has the following beneficial effects:

The present invention solves the problem of autonomous navigation based on sky light field information at the time of the sun and moon alternation. The global sky light field information obtained by the optical sensor equipped with a fisheye lens is filtered to obtain a light field with orderly distribution; according to the characteristics of the filtered global light field, a significant light intensity area with strong energy distribution is selected; in this area, the square weighted centroid method of grayscale is used to obtain a high-precision point on the solar meridian, and the line connecting this point and the center of the light field is the meridian position of the sun; combined with the solar meridian position and the navigation calculation model, the high-precision heading angle of the horizontal carrier is derived, providing strong theoretical and technical support for all-day autonomous navigation based on the sky light field.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of a method for determining a heading based on a significant light intensity area in the sky at the time of the sun-moon transition of the present invention;

Figure 2 is a diagram of the global light field distribution of the sky.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

As shown in FIG1 , a method for determining a heading based on a sky region with significant light intensity at the time of the sun and moon transition of the present invention comprises the following steps:

Step 1: Use an optical sensor equipped with a fisheye lens to obtain the polarized light field of the sky at the time of the sun and moon, and filter the light field to remove interference such as noise;

Step 2: In the filtered light field information, select a significant light intensity area according to the global light field distribution characteristics;

Step 3: In the area of significant light intensity, use the grayscale square weighted centroid method to find the point on the celestial meridian. The line connecting this point and the center of the sky polarized light field is the celestial meridian.

Step 4: Calculate the heading angle of the horizontal carrier at the time of the sun-moon transition by combining the celestial meridian position and the navigation solution model.

Specifically, in step 1, an optical sensor equipped with a fisheye lens is used to collect light intensity images of polarizers at different angles at the time of the sun and moon. , the intensity image/> is the global light intensity field of the sky. In actual light intensity images, noise and other interference are usually included. Perform arithmetic mean linear filtering on the original image to obtain an image with Gaussian and other noise removed./> . For example, the image /> The gray value of the middle point ( i,j ) is/> :

(1)

in, Represents the filter window, whose size is/> ,/> Indicates the filter window/> All coordinate points within Display image/> The middle coordinate is/> The gray value at .

image Contains information on polarized light at four different angles at the same time. In each/> The pixel area contains the light intensity information of the 0°, 45°, 90° and 135° polarizers in the order of upper left, upper right, lower left and lower right pixels. Split into 、/> 、/> and/> Four images, corresponding to the pixel information obtained through 0°, 45°, 90° and 135° polarizers, each image is/> One quarter of the size. Convert to image/> Proceed to the next step

(2)

Specifically, in step 2, since the image It is obtained by an optical camera equipped with a fisheye lens, so it is / > The center is the center of the circle, and the radius is less than or equal to/> The circular area represents the effective area, which is larger than /> The area contains interference such as urban stray light, as shown in Figure 2. Therefore, the image /> Convert to an image containing only the valid area/>

(3)

in, Display image/> Middle/> Line No./> Grayscale value corresponding to the column coordinate, /> Display image/> Middle/> Line No./> Gray value corresponding to the column coordinate; /> Indicates the center of the circle, that is, the image/> Center point;

image The global light intensity field information in the sky is included. The photons emitted by celestial light sources are dispersed in the entire space with the speed of light. The farther away, the greater the dispersion, and the fewer photons per unit area. In fact, the light intensity field is affected by the intensity of the celestial light source, the distance from the light source, and the scattering and absorption of light by the atmosphere. In clear weather, the light intensity at a certain point in the sky can be simplified to be inversely proportional to the square of the distance from the light source.

There is no celestial body information in the field of view, but the lens will record the celestial body light intensity information due to the distortion of the fisheye lens. There will be a crescent-shaped area of significant light intensity surrounded by a dotted line/> , the light intensity in this area is relatively large and has a tendency to gradually decrease from the outer edge to the inner edge. At the same time, this area and its grayscale distribution are symmetrically distributed about the line (meridian) connecting the image center to the celestial body. Therefore, the local area where the sun is located is selected as the image/> The significant light intensity area , as shown in Figure 2, the light intensity in this area is specified as follows:

(4)

in, Indicates the significant light intensity area / > Line No./> The grayscale value corresponding to the column coordinate, Indicates/> Medium light intensity maximum, /> For/> The pixel coordinate set at time .

Specifically, in step 3, the significant light intensity area is determined , considering/> The geometric characteristics of the pixels and the influence of the pixels with large light intensity, and in order to avoid the calculation errors caused by the irregular geometric shape and grayscale distribution, the grayscale square weighted centroid method is used to find the centroid of the significant light intensity area. :

(5)

as shown in picture 2, is a point on the solar meridian, /> Its extension line passes through the center of the sun, so the position of the solar meridian can be determined.

Specifically, in step 4, the carrier is in a horizontal condition, by determining the solar meridian , the azimuth of the solar meridian in the pixel coordinate system can be calculated/> . Through the transformation matrix between pixel coordinate system and image coordinate system/> , the azimuth of the solar meridian in the pixel coordinate system/> Can be converted into the azimuth of the solar meridian in the image coordinate system

(6)

By the intrinsic transformation matrix between the image coordinate system and the carrier coordinate system , the azimuth of the solar meridian in the image coordinate system/> Can be converted into the solar meridian azimuth in the carrier coordinate system/>

(7)

The solar meridian azimuth in the navigation coordinate system is calculated based on the astronomical calendar function combined with the time and position information of the carrier. , then the heading angle of the horizontal carrier in the navigation coordinate system/> Expressed as

(8)

The present invention uses two methods, simulation and field testing, to verify the effect of the embodiment.

(1) Simulation verification

In the simulation, it is assumed that the geographic coordinate system is consistent with the camera system posture, the simulation environment is a clear and cloudless time of the sun and the moon, the solar azimuth is fixed at 45°, and the sky light intensity field image is generated based on the law that the light intensity at a certain point in the sky can be simplified to be inversely proportional to the square of the distance from the light source. Additive noise and multiplicative noise are added to the image to verify the effectiveness of the algorithm. In this embodiment, the additive noise is Gaussian noise with a mean of 0 and a variance of 0.02, and the multiplicative noise is uniformly distributed random noise with a mean of 0 and a variance of 0.5. Compared with the traditional polarization orientation method, the solar azimuth accuracy of the present invention is: when the additive noise is used, the error is 0.08°, and when the multiplicative noise is used, the error is 0.18°; and the polarization orientation solar azimuth accuracy is: when the additive noise is used, the error is 0.23°, and when the multiplicative noise is used, the error is 0.36°. This shows that the present invention has a stronger ability to resist noise interference and can obtain higher accuracy.

(2) Field test verification

In this embodiment, the experimental environment is a clear and cloudless night condition with a 98.6% full moon. The astronomical data involved in the experiment comes from the weather forecast platform 7Timer, and the data of this platform is mainly extracted from the "Global Forecast System" (GlobaForecast System, GFS) numerical model of the National Oceanic and Atmospheric Administration/National Climate and Environmental Prediction Bureau (NOAA/NCEP). The experimental equipment uses the polarization camera PHX050S-PC of Lucid Vision Labs, with the fisheye lens FE185C057HA-1. In the experiment, the camera system is placed horizontally, and a dual-antenna GPS (HX-GPS500A/OEMR982) is used to measure the heading reference; Thinkpad X1 is used for data recording and solution, and GPS data is received as the heading reference.

There is no effective celestial body imaging in the field of view in the short period after sunset and before sunrise, and the global light field of the sky is collected in the time period after sunrise (18:00-18:40 h) and the time period before sunrise (6:00-6:40), respectively. Compared with the polarization orientation method, the average heading angle error in the two time periods after sunset and before sunrise is improved by 0.3433° and 0.8971°, respectively, which further verifies that the method of the present invention can obtain higher-precision heading angle information.

Claims (5)

1. A method for determining a heading based on a significant light intensity area in the sky at the time of the sun and moon transition, characterized in that it comprises the following steps: Step 1: Use an optical sensor equipped with a fisheye lens to obtain the polarized light field of the sky at the time of the sun and moon, and filter the light field to remove noise interference; Step 2: In the filtered light field information, select a significant light intensity area according to the global light field distribution characteristics; Step 3: In the area of significant light intensity, use the grayscale square weighted centroid method to find the point on the celestial meridian. The line connecting this point and the center of the sky polarized light field is the celestial meridian. Step 3.1: Determine the area of significant light intensity , the grayscale square weighted centroid method is used to find the centroid of the significant light intensity area/> : (4) Step 3.2: Find After the point coordinates, /> That is the meridian of the sun, and its extension passes through the center of the sun; Step 4: Calculate the heading angle of the horizontal carrier at the time of the sun-moon transition by combining the celestial meridian position and the navigation solution model; Step 4.1: The carrier is in horizontal condition, by determining the solar meridian , calculate the azimuth of the solar meridian in the pixel coordinate system/> ; Step 4.2: Transformation matrix between pixel coordinate system and image coordinate system , the azimuth of the solar meridian in the pixel coordinate system/> Convert to the azimuth of the solar meridian in the image coordinate system/> : (5) Step 4.3: Use the intrinsic transformation matrix of the image coordinate system and the carrier coordinate system , the azimuth of the solar meridian in the image coordinate system/> Convert to the solar meridian azimuth in the carrier coordinate system/> : (6) Step 4.4: Calculate the solar meridian azimuth in the navigation coordinate system based on the astronomical almanac function combined with the time and position information of the carrier. , then the heading angle of the horizontal carrier in the navigation coordinate system/> Expressed as (7). 2. The method for determining the heading based on the significant light intensity area in the sky at the time of the transition between the sun and the moon according to claim 1, characterized in that step 1 comprises: Step 1.1: Use an optical sensor equipped with a fisheye lens to collect light intensity images of polarizers at different angles at the time of the sun and moon. , the light intensity image is the global light intensity field of the sky; Step 1.2: Light intensity image Perform arithmetic mean linear filtering to obtain an image without noise interference/> ; Step 1.3: Image Contains information on polarized light at four different angles at the same time,/> In each/> The upper left, upper right, lower left and lower right pixels in the pixel area are the light intensity information of the polarizers at 0°, 45°, 90° and 135° respectively; Split into /> , 、/> and/> Four images, corresponding to the pixel information obtained through 0°, 45°, 90° and 135° polarizers respectively; Convert to image/> Proceed to the next step, where (1). 3. The method for determining the heading based on the significant light intensity area in the sky at the time of the transition between the sun and the moon according to claim 2, characterized in that step 2 comprises: Step 2.1: Due to the image It is obtained by an optical camera equipped with a fisheye lens, so the image is Center/> is the center of the circle, and the radius is less than or equal to/> The circular area represents the effective area, which is larger than /> The area contains urban stray light interference; therefore, the image /> Convert to an image containing only the valid area/> ; (2) in, Display image/> Middle/> Line No./> Grayscale value corresponding to the column coordinate, /> Display image/> Middle/> Line No./> Grayscale value corresponding to the column coordinate; /> Indicates the center of the circle, that is, the image/> center; Step 2.2: Image contains the global light intensity field information in the sky. At the time of the sun-moon transition, the light intensity information of the sun and the moon exist in the sky at the same time. The light intensity of the local area where the sun is located is greater than the light intensity of the local area where the moon is located. Therefore, the local area where the sun is located is selected as the image. The significant light intensity area in/> , the light intensity in this area is specified as follows: (3) in, Indicates the significant light intensity area / > Line No./> The grayscale value corresponding to the column coordinate, Indicates/> Medium light intensity maximum, significant light intensity area/> for The pixel coordinate set at time . 4. A non-volatile storage medium, characterized in that the non-volatile storage medium includes a stored program, wherein when the program is executed, the device where the non-volatile storage medium is located is controlled to execute the method according to any one of claims 1 to 3. 5. An electronic device for determining heading for autonomous navigation, characterized in that it comprises a processor and a memory; the memory stores computer-readable instructions, and the processor is used to run the computer-readable instructions, wherein the computer-readable instructions, when running, execute the method described in any one of claims 1 to 3.