阅读说明：本技术 一种基于降维星表的自主星图识别方法 (Autonomous star map identification method based on dimensionality reduction star catalogue ) 是由 踪华 李冰 翟雯婧 姬晓琴 于 2019-11-01 设计创作，主要内容包括：一种基于降维星表的自主星图识别方法,通过建立观测星特征向量,建立星表匹配星表,将观测星o的特征向量与导航星特征向量一一进行比较,特征向量中的元素匹配成功的数量最多且大于一定的门限的导航星特征即作为成功的匹配。若匹配失败,则选取距离观测星o次近邻星为星间几何角度计算基准,重新获得观测星的特征向量,再与星表中的特征向量匹配。(An autonomous star map identification method based on a dimensionality reduction star table comprises the steps of establishing observation star feature vectors, establishing a star table matching star table, comparing the feature vectors of observation star o with navigation star feature vectors one by one, and taking navigation star features with the largest number of successfully matched elements in the feature vectors and larger than a certain threshold as successful matching. If the matching fails, selecting the o-th nearest neighbor from the observation star as the inter-star geometric angle calculation reference, re-obtaining the feature vector of the observation star, and matching the feature vector with the feature vector in the star table.)

1. An autonomous star map identification method based on a dimensionality reduction star table is characterized by comprising the following steps:

1) establishing observation star characteristic vectors, selecting an observation star o closest to the center of a view field, obtaining the angular distance between each observation star and the observation star o and the geometric angle of the distance oa to form a group of vectors, and calculating the vector projection distance;

2) selecting navigation stars, namely selecting the navigation stars in the equal range which can be measured by the star sensor to form a navigation star set; calculating the angular distance between any two fixed stars in the navigation star set, removing one navigation star with equal height from two navigation stars with the distance less than a certain distance threshold xi, and forming a set by the remaining navigation stars to be used as a main star list, wherein the serial numbers of the navigation stars in the main star list are arranged according to the ascending sequence of the red meridians of the navigation stars;

3) matching with star table, for any navigation star o_iFirst, the navigation star within the field range when the optical axis points to it is calculated, and then o is calculated_iThe feature vector of (2);

4) and matching the observation star feature vector with the navigation star feature vector, comparing the feature vector of the observation star o with the navigation star feature vector one by one, wherein the navigation star feature with the maximum number of successfully matched elements in the feature vector and more than a certain threshold is used as the successful matching, and the element matching in the feature vector is determined according to a specific threshold value according to the measurement precision of a star sensor and the star equal range of a star catalogue by combining with an experiment.

2. The identification method according to claim 1, wherein the step 1) comprises the following specific steps: selecting an observation star o closest to the center of a view field and an adjacent star a closest to the observation star o, calculating the distance from other observation stars to the observation star o, taking the observation star oa as a starting edge, calculating a geometric angle between the star o as a vertex and other observation stars and the oa in the same rotation direction, obtaining the angular distance from each observation star to the observation star o and the angle of the distance oa to form a group of vectors, and calculating the vector projection distance.

3. Identification method according to claim 2, characterized in that said features are described by means of geometrical angles between the star point and the stars, in the case of b stars, characterized by a star point i₁And a geometric angle theta₁Geometric angle theta₁The calculation method is as follows:

and the number of the first and second electrodes,

wherein (x)₀,y₀)，(x₁,y₁) The coordinates of the star points of the stars o and b respectively,

(l₁,θ₁) Projected distance d on l ═ theta₁The calculation method comprises the following steps:

4. the identification method according to claim 1, wherein the step 3) comprises the following specific steps:

1) determining the optical axis direction as the navigation star o_iThe right ascension and declination of (1), wherein the right ascension (alpha)_i,α_i∈[0°360°]) Declination (. beta.) of declination_i,β_i∈[-90°,90°]) Range of the right ascension span RangeRa;

2) searching navigation stars in a visual field in a main star table, and storing navigation star right ascension and declination (alpha, beta) in the visual field meeting the conditions into a set Nsubi;

3) construction of navigation star o by using set Nsubi_iCalculating the vector projection distance.

5. The identification method according to claim 4, wherein the range of right ascension spans

Wherein: b_s＝2sin(FOV_x/2)；h_s＝2sin(FOV_y/2)*sin(β_i)；FOV_x,FOV_yIs the field size.

6. The identification method according to claim 4, wherein the right ascension angle α and the declination β satisfy the following condition:

a represents the range of right ascension and the navigation star alpha_iTo navigate star o_iThe red meridian of (1).

7. The identification method according to claim 4, characterized in that said construction of a navigational star o_iThe characteristic vector steps are as follows: selecting a distance Star o_iNearest neighbor a_iCalculating other star-to-star o_iA distance of o_ia_iAs a starting edge, calculateStar o_iCalculating other star to o in the same rotation direction for the vertex_iIs connected to o_ia_iThe geometric angle between the star points obtains the star distance o of each star_iAnd an angular distance of_ia_iThe geometric angle between them, forming a set of vectors (l)₁,θ₁),(l₂,θ₂),…(l_n,θ_n) Then calculate (l)₁,θ₁),(l₂,θ₂),…(l_n,θ_n)

Projected distance d on l ═ theta₁,d₂,…d_nForm a star o_iThe feature vector of (2).

8. The identification method according to claim 1, wherein if the matching fails, the next nearest neighbor to the observation star is selected as the inter-star geometric angle calculation reference, the feature vector of the observation star is obtained again, and then the feature vector is matched with the feature vector in the star table.

Technical Field

The invention belongs to the technical field of astronomical navigation, and particularly relates to an autonomous star map identification method based on a dimension reduction star catalogue.

Background

The star sensor is a high-precision astronomical navigation device, has the advantages of high attitude determination precision, strong autonomy, high reliability and the like, and is widely applied to aerospace vehicles. The autonomous star map recognition is a key technology for realizing autonomous attitude determination by the star sensor, and after the star sensor appears, an autonomous star map recognition method is continuously researched.

The automatic star map identification is to identify a fixed star in an all-day star table by utilizing fixed star information shot by a star sensor and determine the position of the fixed star in an inertial system. Thus, recognition can be accomplished without any pose information. The comparative classical star map recognition algorithms include a triangle recognition method, a matching group algorithm, a grid algorithm, a pyramid algorithm and the like. The methods are researched and applied in a certain period, but a star map identification method with better performance is required to be explored in combination with the current application requirements.

In actual online application, more stars are expected to be identified, which is beneficial to improving the precision and the reliability; the recognition rate is high, and the continuous starlight attitude determination is facilitated; the calculation speed is high, and the improvement of the star light updating frequency is facilitated; the star watch has small capacity, and the cost of the information processor can be reduced.

In a word, the existing autonomous star map recognition algorithm has three main problems that ① is poor in robustness when measuring noise changes, ② navigation star library occupies a large storage space, ③ is complex in calculation, and the operation time is long.

Disclosure of Invention

Aiming at the requirements, the autonomous star map identification method based on the dimensionality reduction star catalogue can conveniently and flexibly identify the star in the field of view of the star sensor, and is high in identification rate, high in speed and small in star catalogue capacity.

The invention is realized by the following technical scheme:

1. establishing observation star feature vector

And selecting an observation star o closest to the center of the field of view and an adjacent star a closest to the observation star o. And calculating the distances from other observation stars to the observation star o, taking the observation star oa as an initial edge, and calculating the geometric angle (in the same rotation direction) between the connection line from the other observation stars to the star o and the oa by taking the star o as a vertex. Obtaining the angular distance between each observation star and the observation star o and the geometric angle of the distance oa to form a group of vectors (l)₁,θ₁),(l₂,θ₂),…(l_n,θ_n). Calculation of (l)₁,θ₁),(l₂,θ₂),…(l_n,θ_n) Projected distance d on l ═ theta₁,d₂,…d_n。

θ₁For example, the calculation method is as follows:

and the number of the first and second electrodes,

wherein (x)₀,y₀)，(x₁,y₁) The coordinates of the star points of the stars o, b, respectively.

(l₁,θ₁) Projected distance d on l ═ theta₁Is calculated by

2. Establishing a star catalogue

(1) Main star watch

① navigation star selection:

selecting navigation stars meeting certain conditions of star and the like to form a navigation star set, wherein the star and the like range of the navigation stars comprises the star and the like range which can be measured (or screened) by the star sensor.

② deleting double stars, namely calculating the angular distance between any two stars in the navigation star set, removing one star with equal height for two navigation stars with the distance less than a certain distance threshold xi (the distance is the same as the threshold value for deleting double stars of observation stars), and forming a set by the remaining navigation stars to be used as a main star list.

③ data structure of main star table

The main star table comprises the serial number of each navigation star in the main star table, the right ascension, the declination, the star and the like of each navigation star, wherein the serial numbers of the navigation stars in the main star table are arranged according to the ascending sequence of the right ascension of the navigation stars.

(2) Matching star watch

And (4) assuming that the optical axis of the star sensor points to the navigation stars in the main star list, and calculating the mode of each navigation star under the condition that the optical axis points to each navigation star, namely the mode of each navigation star. This process can be implemented in three steps. To any one navigation staro_iFirst, the navigation star within the field range when the optical axis points to it is calculated, and then o is calculated_iThe feature vector of (2).

Comparing the feature vector of the observation star o with the feature vector of the navigation star one by one, wherein the navigation star feature with the maximum number of successfully matched elements in the feature vector and more than a certain threshold is taken as the successful matching. If the matching fails, selecting the o-th nearest neighbor from the observation star as the inter-star geometric angle calculation reference, re-obtaining the feature vector of the observation star, and matching the feature vector with the feature vector in the star table.

The autonomous star map identification method based on the dimensionality reduction star catalogue improves the star map identification rate and reduces the star catalogue capacity.

The method utilizes the star angular distance and the star geometric angle information to construct the star model, and adopts the dimension reduction method to reduce the capacity of the star catalogue.

Drawings

FIG. 1 is a schematic view of an inter-satellite geometric angle;

FIG. 2 is a method for dimension reduction of star eigenvectors.

Detailed Description

1. Establishing observation star feature vector

And selecting an observation star o closest to the center of the field of view and an adjacent star a closest to the observation star o. And calculating the distances from other observation stars to the observation star o, taking the observation star oa as an initial edge, and calculating the geometric angles (in the same rotation direction) between the other observation stars and the oa by taking the star o as a vertex. Obtaining the angular distance between each observation star and the observation star o and the angle of the distance oa to form a group of vectors (l)₁,θ₁),(l₂,θ₂),…(l_n,θ_n). Calculation of (l)₁,θ₁),(l₂,θ₂),…(l_n,θ_n) Projected distance d on l ═ theta₁,d₂,…d_n。

At a star angular distance of l₁And theta₁For example, the calculation method is as follows:

and the number of the first and second electrodes,

(l₁,θ₁) Projected distance d on l ═ theta₁Is calculated by

2. Establishing a star catalogue

(1) Main star watch

① navigation star selection:

selecting navigation stars meeting certain conditions of star and the like to form a navigation star set, wherein the star and the like range of the navigation stars comprises the star and the like range which can be measured (or screened) by the star sensor.

② deleting double stars, namely calculating the angular distance between any two stars in the navigation star set, removing one star with equal height for two navigation stars with the distance less than a certain distance threshold xi (the distance is the same as the threshold value for deleting double stars of observation stars), and forming a set by the remaining navigation stars to be used as a main star list.

③ data structure of main star table

The main star table comprises the serial number of each navigation star in the main star table, the right ascension, the declination, the star and the like of each navigation star, wherein the serial numbers of the navigation stars in the main star table are arranged according to the ascending sequence of the right ascension of the navigation stars.

(2) Matching star watch

And (4) assuming that the optical axis of the star sensor points to the navigation stars in the main star list, and calculating the mode of each navigation star under the condition that the optical axis points to each navigation star, namely the mode of each navigation star. This process can be implemented in three steps. To any one navigation star o_iFirst, the navigation star within the field of view when the optical axis points to it is calculated, and thenCalculating o_iThe feature vector of (2).

The following is to calculate any one navigation star o_iThe calculation of the pattern is an example, and the process is explained in detail.

① calculating the optical axis pointing direction of star sensor to the navigation star o_iAnd (3) navigation star set in the view field range of the hour star sensor:

I. determining optical axis pointing

The optical axis direction is the navigation star o_iThe right ascension and declination; wherein the Chijing (alpha)_i,α_i∈[0° 360°]) Declination (. beta.) of declination_i,β_i∈[-90°,90°])。

Calculating the Chijing span Range

Wherein: b_s＝2sin(FOV_x/2)；h_s＝2sin(FOV_y/2)*sin(β_i)；

FOV_x,FOV_yIs the field size.

Searching for navigational stars within the field of view in the Master Star Table

The right ascension and declination (α, β) of the navigation star in the field of view need to satisfy the following condition and are stored as a set Nsubi.

② construction of navigation Star o Using set Nsubi_iFeature vector of

The calculation method is similar to the calculation method of the feature vector of the observation star. Selecting a distance Star o_iThe nearest neighbor a. Calculating other Observation Star to Star o_iA distance of o_ia_iAs the starting edge, calculate the star o_iAs the vertex, other stars and o_ia_iThe geometric angle therebetween (in the same rotational direction). Obtaining the distance star o of each observation star_iAngular distance and distance o_ia_iForm a set of vectors (l)₁,θ₁),(l₂,θ₂),…(l_n,θ_n). Then calculate (l)₁,θ₁),(l₂,θ₂),…(l_n,θ_n) Projected distance d on l ═ theta₁,d₂,…d_nConstitute a star N_iThe feature vector of (2). By using the method, the characteristic vectors of all the navigation stars are obtained, and the characteristic vectors are arranged according to the ascending sequence of the characteristic elements, so that a navigation star characteristic star table is formed.

Comparing the feature vector of the observation star o with the feature vector of the navigation star one by one, wherein the navigation star feature with the maximum number of successfully matched elements in the feature vector and more than a certain threshold is taken as the successful matching. If the matching fails, selecting the o-th nearest neighbor from the observation star as the inter-star geometric angle calculation reference, re-obtaining the feature vector of the observation star, and matching the feature vector with the feature vector in the star table.