CN100342213C - Method for recognising star map based on triangle character - Google Patents

Abstract

The present invention belongs to the spaceflight technical field, which relates to the improvement of a star map identifying method. The method of the present invention comprises the following steps: 1. making and storing star pair databank corresponding to angular distance; 2. selecting an observing triangle; 3. identifying the triangle; 4. verification. The present invention has the advantages of storing space saving, no accurate luminance information need, strong fault tolerance ability and quick searching and identifying speed.

Description

A kind of method for recognising star map based on triangle character

Technical field

The invention belongs to the spationautics field, relate to improvement method for recognising star map.

Background technology

Star sensor is a kind of high precision that extensively adopts in the current aerospacecraft, the attitude measurement parts of high reliability, its principle of work is: CCD (perhaps CMOS) imageing sensor is taken the starry sky image in the current field range, image is through signal Processing, extract position (and brightness) information of celestial body in the observation visual field, and in navigational star table, find the correspondence coupling of observation star by star Pattern Recognition Algorithm, utilize these coupling stars to calculating the three-axis attitude of star sensor at last.Star Pattern Recognition Algorithm is a core in the star sensor.In existing numerous star Pattern Recognition Algorithm, the triangle algorithm is the most general a kind of method for recognising star map of using from now on, it obtains extensive studies and the application of many reality is arranged, as the Oersted moonlet of Denmark, the miniature star tracker of DIGISTAR I of the U.S. etc.Triangle is to be recognition feature with three triangles that star is constituted, if observation trigonometric sum navigation triangle can mate, then must satisfy simultaneously

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$|d(j,k)-{\mathrm{<figure-callout\; id="23"\; label="d\; m"\; filenames="C20041010258500112.png"\; state="\{\{state\}\}">d</figure-callout>}}_m^{}|\&le;\mathrm{\&epsiv;}$

$|d(i,k)-{\mathrm{<figure-callout\; id="13"\; label="d\; m"\; filenames="C20041010258500111.png"\; state="\{\{state\}\}">d</figure-callout>}}_m^{}|\&le;\mathrm{\&epsiv;}$

As shown in Figure 1, d _m ¹², d _m ²³And d _m ¹³Be respectively the angular distance of observation three sides of a triangle correspondence, d (i, j), d (j, k) and d (i k) is respectively the angular distance of three limit correspondences of navigational triangle.Liebe diabolo algorithm the earliest studies, and he stores the navigational triangle that nautical star can constitute for search matched.The triangle algorithm of its proposition is picked out 1000 stars and is made up the navigation triangle from 8000 nautical stars, required memory capacity still needs 1MByte, and the navigation triangle of being stored is 185000.The high energy of this recognition methods obtains 94.6% discrimination, and be 10s the averaging time of whole day identification.

Because all possible navigational triangle of storage, therefore traditional triangle algorithm generally needs bigger storage space, because too much navigational triangle comprises a large amount of redundant informations, makes that the recognition time of algorithm is long simultaneously, and discrimination is not high yet.People such as Quine and Heide proposes improved triangle algorithm respectively on the basis of Liebe triangle algorithm, its basic thought is roughly the same, and promptly utilizing monochrome information is that every star is determined a specific triangle.Adopt such method, every star is only used triangle of storage, thereby makes the capacity of navigational triangle database significantly reduce, and discrimination and recognition time also increase than traditional triangle algorithm.But because the accurate monochrome information of this method utilization needs the conversion between the apparent magnitude and the instrument magnitude.Because imaging system is often very limited to the resolving power of brightness, makes these methods be subjected to certain limitation in application.

Summary of the invention

The objective of the invention is: can bring memory capacity huge at all navigational triangles of direct storage, many and the Quine of redundant coupling and Heide select triangle like that to the requirement of monochrome information problem such as relative harshness again, diabolo algorithm of the present invention improves, a kind of method that adopts the storage star form of angular distance to be realized the triangle coupling is proposed, to significantly reduce memory capacity, simultaneously, accelerate recognition speed.

Technical scheme of the present invention is: a kind of method for recognising star map based on triangle character, it is characterized in that,

1.1, structure and the storage star corresponding with angular distance be to database, scanning screening navigational star table, if the angular distance that has two stars is less than d, then store this angular distance and the right sequence number of this star, d be the visual field to angular distance, when the visual field is 12 ° * 12 °, get d=12  °, store the right sequence number of the right angular distance of all stars and this star and constitute the star corresponding with angular moment to database, the right storage of star is arranged according to the big or small ascending order of angular distance;

1.2, select the observation triangle, from the observation star chart, pick out 6 the brightest stars, with any three stars wherein form the observation triangle to be selected that might form, if 6 of observation star number order less thaies, then utilize all observation stars to form observation triangle to be selected, then, from observation triangle to be selected, select an observation triangle, choose and observe leg-of-mutton principle be:

1. the preferential observation triangle of selecting the brightest star to constitute, establishing the brightness that constitutes leg-of-mutton three stars is M ₁, M ₂And M ₃, brightness is weighed with the gray-scale value of asterism, definition M=M ₁M ₂M ₃, the triangle that preferential selection has minimum M value;

2. preferentially select the less observation triangle of angular distance value, under the roughly suitable situation of M value, preferentially select the less triangle of angular distance value, promptly preferentially be chosen in the triangle of longest edge angular distance value minimum in three limits; According to above principle, observation triangle to be selected is sorted, the forward triangle that sorts will be used for discerning successively,, if discern correct result, the triangle that then comes the back will be skipped over; Otherwise, select remaining triangle in order successively and discern;

1.3, leg-of-mutton identification,

1.3.1, to seek the star that mates with leg-of-mutton three angular distances of observation right, establishes d _m ¹², d _m ²³And d _m ¹³Be i.e. three angular distances of observation three sides of a triangle, find its coupling star right at star respectively in to database, establish d according to these three angular distances _m ¹², d _m ²³And d _m ¹³Coupling star pair set be respectively C (d _m ¹²), C ( _m ²³) and C (d _m ¹³), its star that comprises is n (d to number _m ¹²), n (d _m ²³) and n (d _m ¹³);

1.3.2, carry out triangle coupling, the definition of triangle coupling is: it is right to seek three stars $p_{}$ ${}_1\&Element;C\left(d_m^{12}\right),$ ${\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="C20041010258500111.png,C20041010258500112.png"\; state="\{\{state\}\}">p</figure-callout>}}_2\&Element;C\left(d_m^{23}\right),$ ${\mathrm{<figure-callout\; id="3"\; label="p"\; filenames="C20041010258500122.png,C20041010258500131.png"\; state="\{\{state\}\}">p</figure-callout>}}_3\&Element;C\left(d_m^{13}\right),$ And satisfy p ₁, p ₂And p ₃End to end, promptly have between any two and a common star is only arranged, satisfy (the p of such condition ₁, p ₂, p ₃) constitute and observe leg-of-mutton coupling triangle;

Searching method below adopting is sought qualified (p ₁, p ₂, p ₃), its concrete steps are as follows:

1. scan C (d _m ¹²), all stars in the set all are changed to I to the nautical star state that is comprised, and write down with this set in the sequence number j of right another star of each nautical star composition star;

2. scan C ( _m ²³), if this set culminant star has been changed to I to the state of the nautical star that comprised, then the status indication with this nautical star is changed to II, and writes down the sequence number k that forms another right nautical star of star with it;

3. scan C (d _m ¹³), if $(j,k)\&Element;C\left(d_m^{13}\right),$ Then find a coupling triangle, will with (j, k) state of forming right another nautical star i of star becomes III by II, (i, j k) be and navigational triangle that the observation triangle mates; Find out navigational triangle all and observation triangle coupling;

1.4, the checking, the navigational triangle with observation triangle coupling that utilization is found produces a width of cloth and is called simulation star chart with reference to star chart, compare with original observation star chart, if all can find corresponding observation star in the less radius of neighbourhood in the star chart in observation with reference to the star in the star chart, promptly think consistent with the observation star chart with reference to star chart, then identification is correct; Otherwise the navigational triangle of other couplings of checking that use the same method if reference star chart that generates and observation star chart are all inconsistent, is then observed the triangle recognition failures; Continuation is chosen the forward triangle of ordering and is repeated identical identifying from remaining observation triangle, till identification is correct.

Advantage of the present invention is: improved triangle algorithm proposed by the invention is compared its advantage with triangle algorithm in the past and is shown:

1. adopt the method for angular distance coupling to come the observation triangle is discerned, the form of angular distance storage can be saved a lot of storage spaces.

2. select brighter star and form the observation triangle, do not need accurate monochrome information.Select a plurality of observation triangles and discern, have stronger fault-tolerant ability.

3. utilize status indicator to carry out leg-of-mutton identification, have the speed of very fast search identification.

4. introduce the checking link, not only can verify the correctness of identification, screen the redundancy coupling, and mate star for star as much as possible in the observation star chart finds its correspondence.The checking link also provides rough attitude output, and is extremely important to identification and Tracking Recognition that initial attitude is arranged.

Description of drawings

Fig. 1 is general triangle recognition methods synoptic diagram.

Fig. 2 is a triangle identifying synoptic diagram of the present invention.

Fig. 3 is the nautical star that distributes on the celestial sphere and the corresponding synoptic diagram of the observation star in the visual field.

Fig. 4 is the main program flow chart of the inventive method.

Fig. 5 is the influence of asterism position noise to identification.

Fig. 6 is the influence of magnitude noise to identification.

Embodiment

Below the present invention is described in further details.

Generation that star is right and storage.

The present invention adopts the form of angular distance coupling to realize leg-of-mutton coupling, and the star of therefore necessary one of structure earlier and angular distance correspondence is to database.Do not consider the restriction of visual field, can to form N (N-1)/2 star right for N nautical star in theory, be much smaller than the leg-of-mutton number N (N-1) that may form (N-2)/6.The right generative process of star is as follows: scanning screening back navigational star table, if the angular distance that has two stars less than d, is then noted the sequence number of this angular distance and two stars (star to).Here, d be the visual field to angular distance, when the visual field is 12 ° * 12 °, get d=12  °.The right storage of star is arranged according to the big or small ascending order of angular distance.For convenience star is carried out match search to angular distance, all angular distances are divided into a lot of segments, the angular distance of each segment representative is spaced apart λ, stores 0.1 ° 〉=λ＞0 then.Like this, calculate that the angular distance of two observation stars just can be very fast find may be right with the navigation star of its coupling.

Select the observation triangle.

Because the information that provides of the higher star of brightness ratio is reliable, arrived easilier by image capture sensor, therefore, the present invention preferentially selects the brightest star and forms the observation triangle in the observation star chart.Different with triangle algorithm in the past is that the present invention chooses a unique observation triangle to discern, but therefrom chooses one group of brighter star, forms an observation triangle arbitrarily and discerns.If should observe the triangle recognition failures, then recomposition another one observation triangle is discerned, up to obtaining correct being identified as.Therefore, this method only needs rough monochrome information, need not point-device monochrome information so that strict comparison is done in brightness.By experiment, from the observation star chart, pick out 6 the brightest stars in order to form the observation triangle.If 6 of observation star number order less thaies are then selected all observation stars.The leg-of-mutton number that 6 stars can be formed is $C_6^3=20$ 。For 20 possible observation triangles, the principle of choosing is:

1. the preferential observation triangle of selecting the brightest star to constitute.If constituting the brightness of leg-of-mutton three stars is M ₁, M ₂And M ₃(brightness is weighed with the gray-scale value of asterism), definition M=M ₁M ₂M ₃, the triangle with minimum M value is preferred.

2. preferentially select the less observation triangle of angular distance value.The angular distance value is big more, and star is many more to number to the star of database respective bins, and the possibility of redundant coupling is also big more.Therefore, under the roughly suitable situation of M value, should preferentially select the less triangle of angular distance value.Here, the present invention adopts the principle of longest edge minimum, and promptly the triangle of longest edge angular distance value minimum is preferred in three limits.

According to above principle, will observe triangle sort.The forward triangle that sorts will be used for discerning successively, if discern correct result, the triangle that then comes the back will be skipped over.Otherwise, select remaining triangle in order successively and discern.

Leg-of-mutton identification.

If d _m ¹², d _m ²³And d _m ¹³Be observation three sides of a triangle (angular distance), find its coupling star right at star respectively in to database according to these three angular distances.If d _m ¹², d _m ²³And d _m ¹³Coupling star pair set be respectively C (d _m ¹²), C (d _m ²³) and C (d _m ¹³), its star that comprises is n (d to number _m ¹²), n (d _m ²³) and n (d _m ¹³).It is right that the process of triangle coupling is actually three stars of searching ${\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="C20041010258500112.png,C20041010258500122.png"\; state="\{\{state\}\}">p</figure-callout>}}_1\&Element;C\left(d_m^{12}\right),$ ${\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="C20041010258500111.png,C20041010258500112.png"\; state="\{\{state\}\}">p</figure-callout>}}_2\&Element;C\left(d_m^{23}\right),$ ${\mathrm{<figure-callout\; id="3"\; label="p"\; filenames="C20041010258500122.png,C20041010258500131.png"\; state="\{\{state\}\}">p</figure-callout>}}_3\&Element;C\left(d_m^{13}\right),$ And satisfy p ₁, p ₂And p ₃End to end, promptly there is and only has a common star between any two.Satisfy (the p of such condition ₁, p ₂, p ₃) can constitute the coupling triangle of observing triangle.

Generally speaking, adopt the method that travels through to carry out leg-of-mutton match search and need n (d _m ¹²) * n (d _m ²³) * n (d _m ¹³) inferior comparison operation, if the star that the coupling star pair set of every limit correspondence comprises is about 100 to number, then once coupling just needs 10 ⁶Inferior comparison operation, such search need consume the considerable time.For fear of this situation, the present invention adopts a kind of searching method simply fast, and it seeks qualified (p by status indicator is set ₁, p ₂.p ₃).As shown in Figure 2, its concrete steps are as follows:

1. scan C (d _m ¹²), all stars in the set all are changed to I to the nautical star state that is comprised, and write down with this set in the sequence number j of right another star of each nautical star composition star;

2. scan C (d _m ²³), if this set culminant star has been changed to I to the state of the nautical star that comprised, then the status indication with this nautical star is changed to II, and writes down the sequence number k that forms another right nautical star of star with it;

3. scan C (d _m ¹³), if $(j,k)\&Element;C\left(d_m^{13}\right),$ Then find a coupling triangle, will with (j, k) state of forming right another nautical star i of star becomes III by II, (i, j k) be and navigational triangle that the observation triangle mates; Find out navigational triangle all and observation triangle coupling; Employing is provided with the method for status indicator, and searching times only is n (d _m ¹²)+n (d _m ²³)+n ( _m ¹³).

Checking.

By above identifying, the navigational triangle that the observation triangle can mate may be not unique, at this moment must rely on additive method and further screen.In order to realize this purpose, we introduce the checking link, and it has mainly acted on:

1. the correctness of checking identification filters out wrong coupling simultaneously.

2. find its coupling star, the precision that helps Tracking Recognition like this and improve Attitude Calculation for observation star as much as possible in the observation star chart.

3. can provide rough attitude information.

The basic thought of checking link is: if identification is correct, promptly navigational triangle is the leg-of-mutton correct coupling of observation, then utilize these couplings calculate attitude should be accurately.And then the star chart (being called with reference to star chart) of the width of cloth simulation that produces according to this attitude also should consistent with original observation star chart (position of asterism be corresponding consistent).Be illustrated in figure 3 as the nautical star that distributes on the celestial sphere and the corresponding synoptic diagram of the observation star in the visual field.Under the correct situation of identification, not only navigational triangle and the corresponding coupling of observation triangle, its separately other star of neighborhood also should be corresponding coupling.

If all can find corresponding observation star in the less radius of neighbourhood in the star chart in observation with reference to the star in the star chart, promptly think consistent with reference to star chart and observation star chart, then identification is correct, the algorithm end.Otherwise the navigational triangle of other couplings of checking that use the same method if reference star chart that generates and observation star chart are all inconsistent, is then observed the triangle recognition failures.Continuation is chosen the forward triangle of ordering and is repeated identical identifying from remaining observation triangle.Correctly do not discerned if there is the observation triangle, then the entire identification process failure is returned.The main flow chart of the inventive method as shown in Figure 4.From the observation star chart, select 6 the brightest stars earlier, form triangle, triangle is sorted, select the forward triangle of ordering successively and discern according to brightness principle and the minimum principle of longest edge with these 6 stars.Identifying is: three pairing angular distances in limit of first diabolo carry out the angular distance coupling, and the navigational triangle that can mate by the method search of status indicator is judged the correctness of identification and rejected wrong coupling with the checking link at last then.

Emulation experiment and performance evaluation.

In order to assess the performance of the inventive method, adopted the star chart of simulation to carry out emulation experiment.The parameters of emulation experiment is as shown in table 1.Angular distance λ=0.05 ° at interval in the experiment.Emulation experiment is mainly investigated the influence of identification with regard to asterism position noise and magnitude (brightness) noise.

The position noise of asterism is mainly derived from the error of asterism center segmented positioning method.In the experiment, the star map image for simulation generates adds Gaussian distributed on true asterism position, and average is 0, the noise that standard deviation from 0 to 2 pixel changes.Its recognition result as shown in Figure 5.Under the situation of noise level very little (σ＜0.5), the discrimination of improved triangle algorithm nearly can reach 100%, and this discrimination of 94.6% than traditional triangle shape algorithm improves a lot.When σ=2 pixels, the discrimination of traditional triangle shape algorithm quickly falls to about 70%, still can reach about 97% and improve triangle algorithm identified rate.

The magnitude noise has reflected the sensitivity of imageing sensor to brightness.In the experiment, in the star image simulation process, magnitude is added that the average of Gaussian distributed is 0, standard deviation is from 0 to the 1Mv noise that changes, and is reflected in to be the noise of asterism gradation of image amplitude in the star chart.Equally, get 1000 width of cloth star charts from the whole day ball at random and discern statistics, Fig. 6 is a statistics.As can be seen from the figure, improved triangle algorithm has stronger robustness to the magnitude noise.Still can reach 93% discrimination when the magnitude noise standard deviation is 1Mv, during less than 0.5Mv, discrimination is near 100% at the magnitude noise standard deviation.The improvement algorithm of Quine and Heide is responsive to the magnitude noise ratio, and when magnitude noise during to certain level, discrimination decline is very fast.

Claims (2)

1, a kind of method for recognising star map based on triangle character is characterized in that,

1.1, structure and the storage star corresponding with angular distance be to database, scanning screening navigational star table, if the angular distance that has two stars is less than d, then store this angular distance and the right sequence number of this star, d be the visual field to angular distance, when the visual field is 12 ° * 12 °, get d=12  °, store the right sequence number of the right angular distance of all stars and this star and constitute the star corresponding with angular moment to database, the right storage of star is arranged according to the big or small ascending order of angular distance;

1.2, select the observation triangle, from the observation star chart, pick out 6 the brightest stars, with any three stars wherein form the observation triangle to be selected that might form, if 6 of observation star number order less thaies, then utilize all observation stars to form observation triangle to be selected, then, from observation triangle to be selected, select an observation triangle, choose and observe leg-of-mutton principle be:

1. the preferential observation triangle of selecting the brightest star to constitute, establishing the brightness that constitutes leg-of-mutton three stars is M ₁, M ₂And M ₃, brightness is weighed with the gray-scale value of asterism, definition M=M ₁M ₂M ₃, the triangle that preferential selection has minimum M value;

2. preferentially select the less observation triangle of angular distance value, under the roughly suitable situation of M value, preferentially select the less triangle of angular distance value, promptly preferentially be chosen in the triangle of longest edge angular distance value minimum in three limits; According to above principle, observation triangle to be selected is sorted, the forward triangle that sorts will be used for discerning successively, if discern correct result, the triangle that then comes the back will be skipped over; Otherwise, select remaining triangle in order successively and discern;

1.3, leg-of-mutton identification,

1.3.1, to seek the star that mates with leg-of-mutton three angular distances of observation right, establishes d _m ¹², d _m ²³And d _m ¹³Be i.e. three angular distances of observation three sides of a triangle, find its coupling star right at star respectively in to database, establish d according to these three angular distances _m ¹², d _m ²³And d _m ¹³Coupling star pair set be respectively C (d _m ¹²), C (d _m ²³) and C (d _m ¹³), its star that comprises is n (d to number _m ¹²), n (d _m ²³) and n (d _m ¹³);

1.3.2, carry out triangle coupling, the definition of triangle coupling is: it is right to seek three stars $p_1\&Element;C\left(d_m^{12}\right),$ $p_2\&Element;C\left(d_m^{23}\right),$ $p_3\&Element;C\left(d_m^{13}\right),$ And satisfy p ₁, p ₂And p ₃End to end, promptly have between any two and a common star is only arranged, satisfy (the p of such condition ₁, p ₂, p ₃) constitute and observe leg-of-mutton coupling triangle;

Searching method below adopting is sought qualified (p ₁, p ₂, p ₃), its concrete steps are as follows:

1. scan C (d _m ¹²), all stars in the set all are changed to I to the nautical star state that is comprised, and write down with this set in the sequence number j of right another star of each nautical star composition star;

2. scan C (d _m ²³), if this set culminant star has been changed to I to the state of the nautical star that comprised, then the status indication with this nautical star is changed to II, and writes down the sequence number k that forms another right nautical star of star with it;

3. scan C (d _m ¹³), if $(j,k)\&Element;C\left(d_m^{13}\right),$ Then find a coupling triangle, will with (j, k) state of forming right another nautical star i of star becomes III by II, (i, j k) be and navigational triangle that the observation triangle mates; Find out navigational triangle all and observation triangle coupling;

1.4, the checking, the navigational triangle with observation triangle coupling that utilization is found produces a width of cloth and is called simulation star chart with reference to star chart, compare with original observation star chart, if all can find corresponding observation star in the less radius of neighbourhood in the star chart in observation with reference to the star in the star chart, promptly think consistent with the observation star chart with reference to star chart, then identification is correct; Otherwise the navigational triangle of other couplings of checking that use the same method if reference star chart that generates and observation star chart are all inconsistent, is then observed the triangle recognition failures; Continuation is chosen the forward triangle of ordering and is repeated identical identifying from remaining observation triangle, till identification is correct.

2, method for recognising star map according to claim 1, it is characterized in that, at structure and the storage star corresponding during to database with angular distance, all angular distances are divided into a lot of segments, the angular distance of each segment representative is spaced apart λ, store then, the value of λ is relevant with the position noise level of asterism, generally gets 0.1 ° 〉=λ＞0.

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