CN102840861B - Navigational star screening method for star sensors - Google Patents

Abstract

The invention relates to a navigational star screening method for star sensors, which includes the following steps: (1) according to the limiting magnitude of a star sensor, the stars of the original star catalogue of the whole celestial sphere are filtered and a star number threshold Nth is determined; (2) the number of the remaining stars of the star sensor in the field of view of the current sky area is set as N; if N is less than or equal to Nth, then all the remaining stars are chosen as navigational stars, and step 3 is executed; and if N is greater than Nth, then the navigational stars in the field of view of the current sky area are segmented and screened by a multi-scale image plane; (3) after the navigational stars in the field of view of the current sky area are screened, the star sensor turns to the next direction to repeat navigational star screening in step 2 until the whole celestial sphere is traversed. The multi-scale image plane segmentation and screening method adopted in the invention can be adapted to the variation in the star numbers of different sky areas to delete the redundant stars of sky areas with high star distribution density and keep all the stars of low-density sky areas, and moreover, the distribution of the screened navigational stars is even.

Description

A kind of method of the screening nautical star for star sensor

Technical field

The invention belongs to celestial navigation technical field, relate to a kind of method of the screening nautical star for star sensor.

Background technology

Star sensor passes through importance in star map recognition, the feature of comparative observation star group and navigation star group, identifies observation star, determines their coordinates in body coordinate system and inertial coodinate system, thus measure the attitude of satellite, be the satellite attitude measurement instrument that in modern space industry, a kind of precision is the highest.Importance in star map recognition is the core technology of star sensor, setting up guide star catalog is the important prerequisite identifying star chart, choose reasonable nautical star is for reduction navigation star stack features similitude, improve importance in star map recognition speed and importance in star map recognition success rate, strengthen the anti-pseudo-star interference performance of star sensor, improve attitude measurement accuracy significant.

When nautical star is evenly distributed on whole day ball, the star stack features redundancy of nautical star is little, importance in star map recognition stability is high, and usually with Distribution of guide stars Evaluation for Uniformity preferably (screening) algorithm, current nautical star preferably (screening) algorithm roughly can be divided into two large classes.

First kind algorithm is with nautical star being uniformly distributed as starting point at whole day ball.Unit celestial sphere projects in plane by the orthogonal grid method that the soughing of the wind in forest trees in 1998 etc. propose, and this projection plane of quadrature divide, is divided into much non-cross homalographic sky district by whole day ball, choosing a fixed star in district at each day is nautical star.Due to sky district length-width ratio along with latitude changes, nautical star density is also uneven.Samaan in 2004, the sphere Method of Partitioning (The Spherical Patches method) that Malak A etc. propose, fixed elevation spiral collimation method (The Fixed-Slope Spiral method) and charged particle method (The Charged Particles method) scheduling algorithm divide equally celestial sphere, the relation of each day district's length-width ratio and present position is little, the Distribution of guide stars obtained also evenly.Within 2004, be published in the nautical star optimization algorithm based on Boltzmann entropy on ELECTRONICS LETTERS the 40th volume the 2nd phase, from two selected nautical stars, choose other nautical stars one by one, make all Boltzmann entropies of nautical star that selected minimum, this algorithm effectively can delete redundant star, obtains uniform whole day ball Distribution of guide stars.The visual field of the less consideration star sensor of this type of algorithm and the number of nautical star in each Tian Qu visual field, be uniformly distributed although can realize nautical star, when visual field is very large, the nautical star that at every turn can observe still has redundancy.

Equations of The Second Kind algorithm, from the be uniformly distributed of nautical star on the celestial sphere of local, realizes being uniformly distributed on whole day ball.Li Lihong in 2000 etc. propose magnitude method of weighting, give different weights to every fixed star according to magnitude, the fixed star of low magnitude has high weight, the fixed star of high magnitude has low weights, nautical star is chosen according to weights, algorithm is better than orthogonal grid method, but the less consideration star place of this algorithm, Distribution of guide stars uniformity has much room for improvement.Texas A & M university Hye-Young Kim in 2002 etc. propose self-organizing nautical star Algorithms of Selecting, reach the prerequisite of certain navigation star number in the visual field meeting arbitrary axis sensing under, according to the position relationship of fixed star, select nautical star one by one, Distribution of guide stars is all more even on local and whole day ball.The Regression selection algorithm that Zheng Sheng in 2004 etc. propose is according to the fixed star number that can observe in visual field, based on the method for SVMs, generate Dynamic visual magnitude threshold, nautical star is obtained according to the observation star of this threshold value screening not on the same day in visual field, district, the method can obtain more uniform Distribution of guide stars, but for there being the star sensor of fixed limit magnitude, the Distribution of guide stars that Regression selection algorithm obtains is still even not.

Summary of the invention

The technical problem to be solved in the present invention is to provide a kind of method being suitable for evenly filtering out nautical star for star sensor.

Basic thought of the present invention is, Nei Tian district, visual field due to star sensor only occupies a very little part for whole day ball, so Nei Tian district, this visual field can regard plane domain as, if the image planes of the nautical star imaging arbitrarily in visual field are uniformly distributed, so nautical star also approaches uniformity distribution on whole day ball.Like this, according to the star image density screening nautical star in image planes, the distribution problem of nautical star on whole day ball can be converted to the distribution problem of its star image in image planes.

Under described basic thought, the invention provides a kind of method of the screening nautical star for star sensor, comprising:

Step one, limiting magnitude according to star sensor, make star filtration treatment to the original star catalogue of whole day ball, namely delete double star, variable and the magnitude fixed star higher than limiting magnitude; And according to star Pattern Recognition Algorithm determination star number threshold value N _th;

Step 2, described star sensor are set to N, if N≤N in the quantity when the residue star in visual field, district's day before yesterday _th, then described residue star all elects nautical star as, performs step 3;

If N > is N _th, then described when the nautical star in visual field, district's day before yesterday by multiple dimensioned image planes segmentation screening, its step is as follows:

Described residue star is imaged onto image planes by step (1), these image planes is divided into line number is p, columns is the orthogonal grid of q; Each grid in described orthogonal grid is a community;

Step (2) travels through each community successively, checks the quantity of residue star wherein, wherein, if the quantity of a community residue star has many, then retains a wherein the brightest star, deletes all the other stars; Judge the quantity now remaining star, if N≤N simultaneously _th, then set current residual star as nautical star, traversal terminates, and performs step 3; If N > is N _th, then traversal is continued; If after traveling through all communities, N is still greater than N _th, Ze Ba is used as pixel in community, if having star in community, then the gray value of this pixel is non-zero, if without star in community, then the gray value of this pixel is 0, the neighbor cell with residue star after traversal is divided into connected domain, calculates center-of-mass coordinate and the community number of each connected domain;

Step (3) chooses the maximum connected domain of its small area number, be located in this connected domain from the star that the center-of-mass coordinate of this connected domain is nearest be redundant star; If have many from the star that center-of-mass coordinate is nearest in this connected domain, then a wherein the darkest star is redundant star; If the connected domain that community number is maximum has multiple, then a star the darkest in these connected domains is selected to be redundant star; Delete described redundant star; Judge the quantity now remaining star, if N≤N _th, then set current residual star as nautical star, perform step 3; If N > is N _th, then this step (3) is repeated;

Step (4) is if after no longer including connected domain; N is still greater than N _th, then the value of described p and q all subtracts 1, repeats step (1) to (4); Until N≤N _th;

After the screening of step 3, the described nautical star when visual field, district's day before yesterday terminates, described star sensor forwards next orientation to and repeats step 2 to screen nautical star, until traversal whole day ball.

Further, described step (2) if described in one community residue star quantity have many, then retain a wherein the brightest star, the method for deleting all the other stars comprises: pre-defined three two-dimensional arrays Marray, Idarray and MAGarray in described orthogonal grid; If the community that in described orthogonal grid, m is capable, n arranges has and has a star at least, then Marray [m] [n]=1, otherwise be zero; If there are many stars in described community, then and with IDarray [m] [n] and MAGarray [m] [n] record asterisk and the magnitude of a brightest star respectively, and delete all the other stars.

Further, in order to calculate the center-of-mass coordinate of described connected domain fast, the center-of-mass coordinate computational methods in described step (3) are:

$x_c=\frac{\mathrm{\Σ}{x}_i}{k},$ $y_c=\frac{\mathrm{\Σ}{y}_i}{k},$

Wherein x _c, y _cfor the gray scale center-of-mass coordinate of each connected domain, x _i, y _irepresent the sequence number of the row and column at this place, connected domain ZhongiGe community, k represents the community sum in connected domain.

Further, in order to better split image planes; The ratio of the initial value of described p with q and the row, column size of described image planes are than identical.

Compared with prior art, tool of the present invention has the following advantages: the method for the multiple dimensioned image planes segmentation of the employing in (1) the present invention screening can adapt to not the redundant star in the star number change deletion star distribution high density sky district in district on the same day, retain all stars in low-density sky district, and the Distribution of guide stars of screening is even; (2) the present invention is used as community as pixel, the gray value having star then this pixel in community is non-zero, be 0 without the gray value of star then this pixel in community, the neighbor cell with residue star after traversal is divided into connected domain, the center-of-mass coordinate of this connected domain can be calculated fast by the ranks of this connected domain, and effectively can be deleted the redundant star of high density area by this center-of-mass coordinate, make the distribution of residue star trend towards evenly, be i.e. the even nautical star of last acquisition; (3) completed the nautical star screening of whole day ball by star sensor, and the Distribution of guide stars of the whole day ball of screening is even too; (4) ratio of the initial value of described p with q makes the segmentation of community more reasonable with the row, column size of described image planes than identical, and what be convenient to p and q has successively decreased the segmentation of multiple dimensioned image planes.

Accompanying drawing explanation

In order to make content of the present invention be more likely to be clearly understood, below basis specific embodiment and by reference to the accompanying drawings, the present invention is further detailed explanation, wherein

Fig. 1 is the body coordinate system schematic diagram that the present invention is based upon in optical system;

Fig. 2 is the rotation relationship schematic diagram of inertial coodinate system and body coordinate system;

Fig. 3 is the flow chart of the method for screening nautical star of the present invention;

Fig. 4 is the original star chart provided of illustrating;

Fig. 5 is the distribution map according to fixed star in current field after 5 × 5 segmentation image planes;

Fig. 6 is the distribution map remaining star after deleting each community faint star in current field;

Fig. 7 deletes apart from the distribution map remaining star in current field after largest connected territory barycenter the most nearby star;

Fig. 8 is compared with the distribution map remaining star in current field after faint star in deletion 2 largest connected territories;

Fig. 9 is the distribution map of nautical star after fixed star in screening current field;

Figure 10 is according to the distribution map of fixed star in current field after 8 × 8 segmentation image planes;

Figure 11 is the distribution map remaining star after deleting each community faint star in current field;

Figure 12 deletes the distribution map apart from residue star in current field after connected domain barycenter the most nearby star;

Figure 13 is the distribution map according to residue star in current field after 7 × 7 segmentation image planes;

Figure 14 is the distribution map according to residue star in current field after 6 × 6 segmentation image planes;

Figure 15 is the distribution map according to residue star in current field after 5 × 5 segmentation image planes;

Figure 16 is the distribution map according to nautical star in current field after 5 × 5 segmentation image planes process;

Figure 17 is when limiting magnitude is 5.2 grade, the distribution map of nautical star after star filters, before screening;

Figure 18 is when limiting magnitude is 5.2 grades and visual field is 21.91 ° × 16.47 °, uses the present invention to screen the distribution map of rear nautical star on whole day ball;

Figure 19 is when limiting magnitude is 5.2 grades and visual field is 21.91 ° × 16.47 °, screens the probability distribution graph of nautical star star number in front visual field;

Figure 20 is when limiting magnitude is 5.2 grades and visual field is 21.91 ° × 16.47 °, the probability distribution graph of nautical star star number in the rear visual field of screening;

Figure 21 is the front cumulative probability distribution map with screening nautical star star number in rear visual field of screening when limiting magnitude is 5.2 grades and visual field is 21.91 ° × 16.47 °.

Detailed description of the invention

Below in conjunction with drawings and Examples, the present invention is described in detail:

Embodiment 1

Star image high density area has two features, and one is that to there is star image number in equal areas many, and two is that distance between star image is near.The present invention designs the method for the screening nautical star for star sensor according to these two features.

First, according to first feature, along the row, column direction, focal plane of image planes detector, image planes are divided into the rectangular area of multiple homalographic, form an orthogonal grid.Describe for simplifying, each rectangular area is called a community (each grid namely in described orthogonal grid is a community), and the decile interval in row, column direction is called yardstick.Select certain yardstick to split image planes (also claiming as plane), then in practical operation, the line number adopting setting to split image planes is p, columns is that q realizes; If star image high density area contains many stars, the feature large according to the probability be detected compared with bright star, star image signal to noise ratio is high, therefore retain a wherein the brightest star, process all communities by this method.

Then, according to second feature, the residue star of those close together must be in each other in neighborhood, and also namely the community at their places is communicated with, and form a connected domain, star density is higher, and connected domain scope is larger.If delete the star of the barycenter closest to largest connected territory, then connected domain can be made to split into multiple little connected domain, the star density in this region declines.And then from result, select next largest connected territory, according to similar approach reprocessing, until no longer include connected domain.

Utilize this yardstick cannot determine can also delete which star on earth again, then increase and wait point interval, reduce isodisperse, namely the value of p and q all subtracts 1.

Principle of the present invention for convenience of description, now supposes that star sensor body coordinate system is based upon on optical system, as shown in Figure 1.Make optical system be equivalent to ideal image system, H and H ' is respectively its thing, image space principal point, and f is the focal length of optical system, the initial point of star sensor body coordinate system at image space principal point H ' place, X _baxle, Y _baxle, in image space interarea, is parallel to the row and column of image planes detector focal plane, Z respectively _baxle is along optical axis, and as shown in Figure 1, three axles form right-handed coordinate system to its forward.Fixed star S direction cosines vector is in the coordinate system V _b, at X _b, Y _bangle of visual field XFLD on direction, YFLD, the coordinate in image planes is (x _b, y _b).

Be located in inertial coodinate system, optical axis points to (α _c, δ _c), body coordinate system can be obtained by certain way rotatory inertia coordinate system.As shown in Figure 2, inertial coodinate system first around Z axis by+X axis+Y-axis rotation alpha _c, obtain X ' Y ' Z ' coordinate system, new coordinate system again around Y ' axle by+Z ' axially+X ' axle half-twist-δ _c, " coordinate system, this coordinate system is around Z " axle rotates φ to obtain X " Y " Z, obtains body coordinate system X _by _bz _b.

According to the conversion of the setting of above-mentioned star sensor and inertial coordinate and body coordinate, the method for the screening nautical star for star sensor of the present invention, comprising:

Step one, limiting magnitude according to star sensor, make star filtration treatment to the original star catalogue of whole day ball, namely delete double star, variable and the magnitude fixed star higher than limiting magnitude; And according to star Pattern Recognition Algorithm determination star number threshold value N _th;

Step 2, described star sensor are set to N, if N≤N in the quantity when the residue star in visual field, district's day before yesterday _th, then described residue star all elects nautical star as, performs step 3;

If N > is N _th, then described when the nautical star in visual field, district's day before yesterday by multiple dimensioned image planes segmentation screening, its step is as follows:

Described residue star is imaged onto image planes by step (1), these image planes is divided into line number is p, columns is the orthogonal grid of q; Each grid in described orthogonal grid is a community;

Step (2) travels through each community successively, checks the quantity of residue star wherein, wherein, if the quantity of a community residue star has many, then retains a wherein the brightest star, deletes all the other stars; Judge the quantity now remaining star, if N≤N simultaneously _th, then set current residual star as nautical star, traversal terminates, and performs step 3; If N > is N _th, then traversal is continued; If after traveling through all communities, N is still greater than N _th, Ze Ba is used as pixel in community, if having star in community, then the gray value of this pixel is non-zero, if without star in community, then the gray value of this pixel is 0, the neighbor cell with residue star after traversal is divided into connected domain, calculates center-of-mass coordinate and the community number of each connected domain;

Step (3) chooses the maximum connected domain of its small area number, be located in this connected domain from the star that the center-of-mass coordinate of this connected domain is nearest be redundant star; If have many from the star that center-of-mass coordinate is nearest in this connected domain, then a wherein the darkest star is redundant star; If the connected domain that community number is maximum has multiple, then a star the darkest in these connected domains is selected to be redundant star; Delete described redundant star; Judge the quantity now remaining star, if N≤N _th, then set current residual star as nautical star, perform step 3; If N > is N _th, then this step (3) is repeated;

Step (4) is if after no longer including connected domain; N is still greater than N _th, then the value of described p and q all subtracts 1, repeats step (1) to (4); Until N≤N _th;

After the screening of step 3, the described nautical star when visual field, district's day before yesterday terminates, described star sensor forwards next orientation to and repeats step 2 screening nautical star, until traversal whole day ball.

Center-of-mass coordinate computational methods in described step (3) are:

$x_c=\frac{\mathrm{\Σ}{x}_i}{k},$ $y_c=\frac{\mathrm{\Σ}{y}_i}{k},$

Wherein x _c, y _cfor the gray scale center-of-mass coordinate of each connected domain, x _i, y _irepresent the sequence number of the row and column at this place, connected domain ZhongiGe community, k represents the community sum in connected domain.

The ratio of the initial value of described p with q and the row, column size of described image planes are than identical.

Embodiment 2

The basis of embodiment 1 realizes the described method for the screening nautical star of star sensor, and its specific implementation process is as follows:

The first step, makes star filtration treatment to original star catalogue.Delete faint star according to limiting magnitude, delete variable, double star simultaneously, for convenience of subsequent treatment, residue sing data arranges with ascending order according to declination, and according to star Pattern Recognition Algorithm determination star number threshold value N _th, namely select corresponding star Pattern Recognition Algorithm to determine star number threshold value N according to actual needs _th, also can oneself set as required.

Second step, star sensor optical axis points to coordinate (α on whole day ball _i, δ _i) position, α _ior δ _ieach change 1 °, traversal whole day ball.Extract the residue star in each sensing visual field, calculate residue star sum N.If N≤N _th, then described residue star all elects nautical star as; Star sensor optical axis forwards next orientation to, then judges, until star number is greater than threshold value, starts following steps.

The method extracting the residue star in visual field is, first picks out coordinate (α, δ) and meets

|δ-δ _c|≤w _m

Star, wherein w _mrepresent the angle of visual field that star sensor image planes detector diagonal is corresponding.

Above formula limits the upper and lower bound of residue star declination in current field.Because declination δ span is-90 °-90 °, work as δ _i-w _mwhen being less than-90 °, lower limit should being set and being-90 °, similarly, work as δ _i-w _mwhen being greater than 90 °, the upper limit should be set to 90 °, obtains

Residue sing data sorts, by dichotomy method determination declination value just greater than δ by declination _botthe position of star, then reads subsequent data, extracts residue star, until declination value is greater than δ _top.

Then, calculate the orientation of residue star in body coordinate system extracted, be the star of (α, δ) for right ascension and declination, have

$\left[\begin{array}{c}{V}_{\mathrm{bx}}\\ V_{\mathrm{by}}\\ V_{\mathrm{bz}}\end{array}\right]=\left[\begin{array}{ccc}\cos \mathrm{\φ}& \sin \mathrm{\φ}& 0\\ -\sin \mathrm{\φ}& \cos \mathrm{\φ}& 0\\ 0& 0& 1\end{array}\right]\left[\begin{array}{ccc}\cos (90-{\mathrm{\δ}}_i)& 0& -\sin (90-{\mathrm{\δ}}_i)\\ 0& 1& 0\\ \sin (90-{\mathrm{\δ}}_i)& 0& \cos (90-{\mathrm{\δ}}_i)\end{array}\right]\×$

$\left[\begin{array}{ccc}{\cos \mathrm{\α}}_i& \sin {\mathrm{\α}}_i& 0\\ -\sin {\mathrm{\α}}_i& {\cos \mathrm{\α}}_i& 0\\ 0& 0& 1\end{array}\right]\left[\begin{array}{c}\cos \mathrm{\α}\cos \mathrm{\δ}\\ \sin \mathrm{\α}\cos \mathrm{\δ}\\ \sin \mathrm{\δ}\end{array}\right]$

It is at X _b, Y _bangle of visual field XFLD on direction, YFLD are

$\mathrm{XFLD}=-{\mathrm{tg}}^{-1}\left(\frac{V_{\mathrm{bx}}}{V_{\mathrm{bz}}}\right),\mathrm{YFLD}=-{\mathrm{tg}}^{-1}\left(\frac{V_{\mathrm{by}}}{V_{\mathrm{bz}}}\right)$

If establish optical system at X _b, Y _bmaximum field of view angle on direction is W _aand W _b., only have satisfied

|XFLD|≤W _A/2、|YFLD|≤W _B/2

Fixed star just can be observed.Screened the residue star obtained in current field by above formula, also obtain their angle of visual field XFLD, YFLD simultaneously, and their total N.

All stars in visual field are imaged onto image planes, press by the 3rd step

x _b＝ftan(XFLD)，y _b＝ftan(YFLD)

Calculate and record the position of each star image.

4th step, along row, column direction, focal plane, segmentation image planes are the grid of p × q, set up and initialize two-dimensional array Marray, Idarray and MAGarray of three ps corresponding with grid capable q row, the ratio of p with q should be tried one's best with row, column direction, focal plane size than consistent, identical to ensure the yardstick of both direction.During beginning, p and q should get bigger value, to examine or check star distribution density in detail.Array Marray and Idarray is initialized as 0, MAGarray and is initialized as-99.99.

5th step, travels through each community to calculate the community at the star place of extracting.Be (x for coordinate _b, y _b) star image, it is in, and m in image planes is capable, n row community have star image, so

$n=\mathrm{floor}(\frac{p}{2f\tan \left(\frac{w_A}{2}\right)}{x}_b+\frac{p}{2}-1)$

$m=\mathrm{floor}(\frac{q}{2f\tan \left(\frac{w_B}{2}\right)}{y}_b+\frac{q}{2}-1)$

Wherein floor (x) expression gets a nearest integer less than x, Marray [m] [n]=1.If there is the star image of many stars this community, only retain ludcida, IDarray [m] [n] records the fixed star asterisk remained, and MAGarray [m] [n] records its magnitude, upgrade the star screening of residue star sum N, Ji Duoxing community in current field.

6th step, if N≤N _th, return second step, otherwise adopt pixel clustering algorithm (pixel clustering algorithm see author Yang Fan, " Digital Image Processing and analysis ", ISBN 978-7-5124-0188-4) connection field to calculate center-of-mass coordinate, and to screen further.Ji Ba is used as pixel in community, and the star number in community is used as gray value, adopts eight connectivity that image planes grid is divided into multiple connected domain, calculates center-of-mass coordinate and the community number of each connected domain.Choose that connected domain that community number is maximum, delete from the nearest star of center-of-mass coordinate.If many stars are all nearest from center-of-mass coordinate, delete wherein the darkest star.If the connected domain that community number is maximum has multiple, then delete star the darkest in these connected domains.Meanwhile, upgrade N, Marray, and the value of IDarray, MAGarray.If N > is N _th, repeat this step, then find the next maximum connected domain of scope.As N≤N _thtime, the nautical star screening in current field is complete.If N > is N _th, and the community at any two star places is all no longer communicated with (namely without connected domain), then perform next step.

7th step, p and q reduces 1, and increase and divide equally yardstick, the plot area of image planes has a small amount of increase, and distant several star images may can be communicated with again, then performs from the 4th step, until N≤N _th.

8th step, when whole day ball traversal is complete, nautical star screening terminates.

Above-mentioned steps is simplified to flow chart, as shown in Figure 3.

Embodiment 3

On the basis of embodiment 1 and embodiment 2, by the embodiment of two kinds of segmentations yardstick (i.e. the different values of q and p) with further illustrate content of the present invention compared with prior art.

Following embodiment is using SAO star catalogue as original star catalogue; SAO star catalogue (The Smithsonian Astrophysical Observatory Star Catalog/ Shi Misong astrophysics platform star catalogue) is a uranometry star catalogue, is published, comprise 258 altogether, 997 fixed stars in 1966 by Shi Misong astrophysics platform.This star catalogue is compiled by some star catalogues before and is formed, but only includes more than 9.0 grades and accurately measured fixed star voluntarily.Star names in SAO star catalogue starts then digital number by alphabetical SAO and represents, fixed star is with declination subregion, and every 10 Du Wei mono-districts, be divided into 18th district, the fixed star in each district sorts according to right ascension position.

Embodiment one

Choosing described SAO star catalogue is original star catalogue, limiting magnitude is 5.5 grades, the angle of visual field is 20 ° × 20 °, and after original star catalogue star filtration treatment, the star image of residue star in image planes that certain optical axis points in visual field distributes as shown in Figure 4, now have 18 residue stars, the distribution of these stars is even not.Get N _th=7, p and q initial value are all taken as 5, and image planes, by after 5 × 5 segmentations, as shown in Figure 5, have in multiple community and there are many stars, and each community obtains Fig. 6, remains 10 stars after deleting faint star, reservation ludcida.In Fig. 6, the 1 to 5 row, the 1st, 2 row, wherein form a connected domain by five communities, and comprise star image number maximum, this region star density is high.Delete the star closest to this connected domain barycenter, the star density in this region declines.The coordinate of these five stars is (1,1), (2,1), (3,2), (4,1), (5,1), their barycenter is (3,1.25), it is nearest to (3,2), so deletes (3,2) that star, obtains Fig. 7.Now, have 3 connected domains and all contain 2 communities, their connected domain scope is maximum.Wherein the star of the 2nd row the 1st row is the darkest, then delete it.Remaining 2 connected domains contain 2 communities, and scope is maximum, and the star that the 1st row the 3rd arranges is star the darkest in these 2 connected domains, then deletes it.Such residue star number is not more than threshold value N _th, the selection result obtains as shown in Figure 8 and Figure 9.

Embodiment two

Residue star screening in the visual field corresponding to such as Fig. 4, N _thstill be taken as 7, p and q initial value is all taken as 8, image planes, by after 8 × 8 segmentations, as shown in Figure 10, have in multiple community and there are many stars, each community deletes faint star, retain ludcida after, obtain Figure 11.

As in Figure 11, the 1 to 4 row, the 1st, 2 row, wherein form a connected domain by four communities, and comprise star image number maximum, this region star density is high.Delete the star closest to the barycenter of this connected domain, the star density in this region declines.The coordinate of these four stars is (1,1), (2,2), (3,1), (4,1), their barycenter is (2.5,1.25), and it is to (3,1) nearest, so deletes that star of (3,1).Then from result, largest connected territory is selected again, according to similar approach reprocessing, until the community at any two residue star places is all no longer communicated with.Result after process Figure 11 as shown in figure 12, remains star and distributes more even in this yardstick.

Utilize this yardstick cannot determine can also delete which star on earth again, then increase and wait point interval, reduce isodisperse.Image planes are divided into 7 × 7 totally 49 homalographic regions, obtain Figure 13, do similar process according to the method for a upper yardstick.As Figure 14 increases yardstick again, image planes are divided into 6 × 6 process, obtain Figure 15 and 16, the distribution of visible residue star is very even, and namely these remaining stars can be used as nautical star.

Embodiment three

For the method for screening nautical star of the present invention and orthogonal grid method and Boltzmann entropy algorithm are made comparisons, table 1 provides when visual field gets 11.5 ° × 11.5 °, 14 ° × 14 ° respectively, when limiting magnitude gets 6 and 7.5 etc. respectively, the data of screening nautical star result compare.The data of orthogonal grid method and Boltzmann entropy algorithm derive from respectively and are published in paper " A General Method of the automatically selection of guide star " in Proceedings of ICSP ' 98 meeting and 2004 Published in China Pharmacies at " ELECTRONICS LETTERS " the 40th paper " Boltzmann entropy-based guide star selection algorithm for star tracker " of volume the 2nd phase.Adopt the present invention, star number threshold value N _thbe taken as 6, row, column direction isodisperse p and q initial value are all taken as 8, and the guide star catalog Boltzmann entropy set up thus is minimum, and whole day ball uniformity is best.From local celestial sphere uniformity, the nautical star star number maximum that orthogonal grid method and Boltzmann entropy algorithm obtain is comparatively large, and minimum of a value is less, and uniformity is also slightly poor.

Comparing of table 1 the present invention and orthogonal grid method and Boltzmann entropy algorithm

For with Regression selection algorithm, magnitude weighting algorithm and self-organized algorithm compare, and are 8 ° × 8 ° when getting visual field, limiting magnitude between getting 6.5 to 7.9 totally 7 values time, use the present invention to screen the result after nautical star as shown in table 2.Regression selection algorithm, magnitude weighting algorithm and self-organized algorithm data derive from Zheng Sheng in 2004 etc. respectively and are published in " aerospace journal " the 25th " a kind of new nautical star Algorithms of Selecting research " of volume the 1st phase, Li Lihong in 2000 etc. are published in " optical technology " the 26th " autonomous triangle star map recognizer of whole day of a kind of improvement " of volume the 4th phase, Hye-Young Kim in 2002 etc. are published in the paper " Self-organizing Guide Star Selection Algorithm for Star Trackers:Thinning Method " in IEEE on aerospace conference proceedings meeting.

Table 2 shows, the present invention effectively can reduce the star number in high density sky district, and very micro-on the impact of low-density sky district star number, and 95% to navigate star number between 5 to 12 in visual field, district of going up to the sky.Time limiting magnitude is lower, nautical star number is slightly more, and mainly now star number is less than N in some Tian Qu visual field _theven if around there is redundant star in sky district, can not delete.

When limiting magnitude is 6.5 and 7.3, Regression selection algorithm deletes too much star in part sky district, and the sky district navigation star number more than 10% is less than 5, when limiting magnitude is greater than 7.5 grade, the guide star catalog that this algorithm is set up, still have star number in a lot of Tian Qu visual field too many, star number maximum is larger.Use magnitude weighting algorithm and self-organized algorithm screening nautical star, the large percentage in low-density sky district.Along with limiting magnitude increases, use the guide star catalog that self-organized algorithm is set up, redundancy is increasing.The standard deviation of the guide star catalog that the present invention obtains is minimum, and distribution is the most even, is better than magnitude weighting algorithm, self-organized algorithm and regression algorithm.

Nautical star filtering algorithm contrast during 8 °, table 2 × 8 ° of visual fields

Embodiment four

Getting SAO star catalogue is original star catalogue, and limiting magnitude is 5.2 etc., and star sensor detector length-width ratio is 4:3, and visual field is 21.91 ° × 16.47 °, and the initial value of row, column direction isodisperse p and q gets 12 and 9, chooses star number threshold value N _thbe 6.When using the present invention to set up guide star catalog, delete 529 stars altogether, remain 1078 stars.Distribution before Figure 17 and Figure 18 is respectively nautical star screening and after screening on whole day ball, Boltzmann entropy drops to 1.3643 × 10 by original 0.0119 ^-4, Distribution of guide stars evenly.

Traveled through by whole day ball, the nautical star star number distribution before statistics screening and after screening, result as illustrated in figures 19 and 20.In visual field, nautical star star number maximum is by original 47, be reduced to 18, and minimum is 2 to remain unchanged, the star number standard deviation calculated is reduced to 1.87 by original 6.15, average star number is reduced to 9.37 by 13.75, and the uniformity of nautical star on the celestial sphere of local improves.Figure 21 is the cumulative probability distribution of nautical star star number in visual field, when star number is less than 4, two curve co-insides before and after nautical star screening, in visual field, the probability of appearance more than 4 nautical stars is all 99.94%, show that the present invention effectively can reduce the star number amount in star distribution high density sky district, reduce nautical star feature redundancy.

Obviously, above-described embodiment is only for example of the present invention is clearly described, and is not the restriction to embodiments of the present invention.For those of ordinary skill in the field, can also make other changes in different forms on the basis of the above description.Here exhaustive without the need to also giving all embodiments.And these belong to spirit institute's apparent change of extending out of the present invention or change and are still among protection scope of the present invention.

Claims (3)

1., for a method for the screening nautical star of star sensor, comprising:

Step one, limiting magnitude according to star sensor, make star filtration treatment to the original star catalogue of whole day ball, namely delete double star, variable and the magnitude fixed star higher than limiting magnitude; And according to star Pattern Recognition Algorithm determination star number threshold value N _th;

Step 2, star sensor optical axis point to coordinate (α on whole day ball _i, δ _i) position, α _ior δ _ieach change 1 °, traversal whole day ball; Described star sensor is set to N, if N≤N in the quantity when the residue star in visual field, district's day before yesterday _th, then described residue star all elects nautical star as, performs step 3;

If N > is N _th, then described when the nautical star in visual field, district's day before yesterday by multiple dimensioned image planes segmentation screening, its step is as follows:

Described residue star is imaged onto image planes by step (1), and concrete grammar is: all stars in visual field are imaged onto image planes, press

x _b＝f tan(XFLD)，y _b＝f tan(YFLD)

Calculate and record the position of each star image;

These image planes are divided into line number is p, columns is the orthogonal grid of q; Each grid in described orthogonal grid is a community;

Step (2) travels through each community successively, checks the quantity of residue star wherein, wherein, if the quantity of a community residue star has many, then retains a wherein the brightest star, deletes all the other stars; Judge the quantity now remaining star, if N≤N simultaneously _th, then set current residual star as nautical star, traversal terminates, and performs step 3; If N > is N _th, then traversal is continued; If after traveling through all communities, N is still greater than N _th, Ze Ba is used as pixel in community, if having star in community, then the gray value of this pixel is non-zero, if without star in community, then the gray value of this pixel is 0, the neighbor cell with residue star after traversal is divided into connected domain, calculates center-of-mass coordinate and the community number of each connected domain;

Step (3) chooses the maximum connected domain of its small area number, be located in this connected domain from the star that the center-of-mass coordinate of this connected domain is nearest be redundant star; If have many from the star that center-of-mass coordinate is nearest in this connected domain, then a wherein the darkest star is redundant star; If the connected domain that community number is maximum has multiple, then a star the darkest in these connected domains is selected to be redundant star; Delete described redundant star; Judge the quantity now remaining star, if N≤N _th, then set current residual star as nautical star, perform step 3; If N > is N _th, then this step (3) is repeated;

Step (4) is if after no longer including connected domain; N is still greater than N _th, then the value of described p and q all subtracts 1, repeats step (1) to (4); Until N≤N _th;

After the screening of step 3, the described nautical star when visual field, district's day before yesterday terminates, described star sensor forwards next orientation to and repeats step 2 to screen nautical star, until traversal whole day ball.

2. the method for screening nautical star according to claim 1, is characterized in that: the center-of-mass coordinate computational methods in described step (3) are:

$x_c=\frac{\mathrm{\Σ}{x}_i}{k},y_c=\frac{\mathrm{\Σ}{y}_i}{k}$

Wherein x _c, y _cfor the gray scale center-of-mass coordinate of each connected domain, x _i, y _irepresent the sequence number of the row and column at this place, connected domain ZhongiGe community, k represents the community sum in connected domain.

3. the method for screening nautical star according to claim 1 and 2, is characterized in that: the ratio of the initial value of described p with q and the row, column size of described image planes are than identical.