CN102930244A - Pixel distinguishbility-based natural guide post and method for determining landing area - Google Patents

Abstract

The invention relates to a pixel distinguishbility-based natural guide post and a method for determining a landing area, and belongs to the field of deep space exploration. According to the method, on the basis of the characteristic that the distinguishbility of pixel points in a flat area in an image and pixel points in an area which is adjacent to the flat area is low and the distinguishbility of pixel points in areas of meteor craters, rocks and the like and pixel points in areas which are adjacent to the areas is high, pixel points of which the distinguishbility is lower than a preset threshold value are used as candidate points of the landing area, pixel points of which the distinguishbility is higher than the preset threshold value are used as candidate points of the natural guide post, and a set of the candidate points of the natural guide post within a preset radius is used as the natural guide post by calculating the distinguishbility of each pixel point in the image; and morphological expansion is performed on the candidate points of the natural guide post and pixels at the image boundary, the candidate point of the landing area which is covered by expansion operation finally is used as the center of a circle, and distance between the center of the circle and the candidate point, which is close to the center of the circle, of the natural guide post is used as radius to obtain the maximum landing circle. By the method, the landing area can be determined quickly and reliably.

Description

But a kind of natural landmark and touchdown area based on the pixel discrimination determined method

Technical field

The invention belongs to the survey of deep space neighborhood, relate to the correlation technique that image is processed.

Background technology

Natural landmark detects and touchdown area determines it is major issue in the survey of deep space field.In the survey of deep space process, because lander is very remote apart from the earth, the signal transmission has larger time-delay, but therefore needs the attitude of determining self that lander can be autonomous and position and the autonomous touchdown area that finds.

Natural landmark refers in the environment existing, and unartificial setting, can be in order to references object or the pattern that identifies varying environment.Attitude and the position of self determined in the natural landmark detection for lander, carrying out independent navigation has important effect.Existing natural landmark detection method be mostly for planetary surface various landform (such as meteorite crater, rock etc., image appearance features as shown in Figure 1) is carried out natural landmark and is detected.But these class methods are subject to the impact of illumination and concrete landform, can't obtain good result.

And touchdown area determines it also is very important for detector automatically.In the lander landing period, since very remote apart from the earth, rely on ground communications can not satisfy the demand that actual time safety lands, therefore need detector to have the ability of stronger Autonomous determination touchdown area.Existing independent landing area determination method mainly is that the barriers such as rock are determined touchdown area by avoiding obstacles by the meteorite crater of detection planetary surface.Also the textural characteristics of with good grounds planetary surface carries out definite method of touchdown area.The problem of carrying out the definite method of touchdown area by detecting barrier is that the detection of barrier is difficult to accomplish accurately and robust, affected by illumination condition larger.Existing texture analysis method is to be undertaken by the features such as contrast in the statistical regions, also is subject to the impact of the conditions such as illumination.

We make discovery from observation, the barrier of planetary surface, no matter be meteorite crater (Fig. 1 (a)), rock (Fig. 1 (b)), perhaps crackle (Fig. 1 (c)), all have following characteristics: the point on these obstacles borders is (such as 1 among Fig. 1,2,3,4), very high with the degree distinguished of other points in its neighborhood, both be easy to these points and other point are on every side made a distinction.And flat site in point (such as 5,6 among Fig. 1,7), to its around point more similar, substantially can't with make a distinction on every side.We are based on this observation, carry out but natural landmark detected to determine to be unified under the discrimination framework of pixel with touchdown area.

Summary of the invention

Determine the deficiency that method exists with touchdown area and propose that a kind of natural landmark based on the pixel discrimination detects and touchdown area is determined method but the objective of the invention is to detect for above-mentioned natural landmark.

Main contents of the present invention are: the employing video camera obtains the image information below the lander in lander decline process, in the image that each frame gets access to, but calculate the discrimination of each pixel, both the degree distinguished of the pixel in this pixel and its neighborhood.Setting threshold, but discrimination is higher than the pixel of given threshold value as the natural landmark candidate point, with the set of the natural landmark candidate point in the certain radius as natural landmark; But but discrimination is lower than the pixel of given threshold value as the candidate point in safe landing zone, by the pixel on natural landmark candidate point and the image boundary is carried out morphological dilation, to be inflated at last touchdown area candidate point that operation covers as the center of circle, take this center of circle to apart from the distance of its nearest natural landmark candidate point as radius, obtain the maximum circle that can land.

The objective of the invention is to be achieved through the following technical solutions.

But a kind of natural landmark based on the pixel discrimination detects and touchdown area is determined method, and the specific implementation step is as follows:

Step 1: Image Acquisition

Video camera is installed in the below of lander, the image on acquisition ground that can be continuous in lander decline process.

Step 2: but the discrimination of calculating pixel point

If s (p, p ') be pixel p and pixel p ' similarity degree, establish p (s (p, p ')) expression pixel p and pixel p ' similar probability, but the discrimination of definition pixel is this pixel and the entropy of the interior similar probability distribution of pixel of its neighborhood, both

${\mathrm{distinguishbility}}_p=-{\mathrm{\Σ}}_{p^{\′}\∈N_p}p\left(s(p,p^{\′})\right)\log p\left(s(p,p^{\′})\right)---\left(1\right)$

N wherein _pNeighborhood for pixel p.Entropy is larger, but then discrimination is lower.

Step 3: but but determine touchdown area based on the discrimination of pixel

Barrier region is all regarded in zone but discrimination is high and that but the medium pixel of discrimination covers as, but but touchdown area is regarded in the zone that the low pixel of discrimination covers as.But also regard the point on the image boundary as pixel that discrimination is high, both also regarded barrier zone as.The pixel of barrier region is carried out morphological dilations at every turn, pixel around the barrier also is set to barrier region, along with the carrying out of expanding, but touchdown area is more and more less, but but to be inflated at last the touchdown area that operation covers be exactly the center of circle of maximum touchdown area.But maximum can land radius of a circle can by calculate with the nearest expansion of this point before the height discrimination or the distance of the pixel of medium discrimination obtain

Step 4: the natural landmark based on high discrimination pixel detects

But the pixel with height discrimination can separate with the pixel region around it, can be used as natural landmark.But we with the set of the pixel with height discrimination in the certain radius as natural landmark.

Advantage of the present invention

The present invention and other natural landmark and touchdown area determine that method compares, and have the advantage of the following aspects:

(1) with meteorite crater, but but the detection of the detection of the various natural landmark such as rock and touchdown area is unified under the framework of discrimination processes, can obtain simultaneously natural landmark and touchdown area.

(2) obtain maximum can the land round center of circle and radius by non-natural landmark candidate point being carried out morphologic expansive working, can fast and reliable determine to manage to make do the zone, land.

Description of drawings

The various landform of Fig. 1 planetary surface;

But Fig. 2 determines method flow diagram based on natural landmark and the touchdown area of pixel discrimination;

The similar probability distribution graph of pixel in Fig. 3 pixel and its neighborhood;

Fig. 4 maximum can be landed to justify and be determined the method schematic diagram.

Embodiment

Below in conjunction with drawings and Examples the present invention is elaborated.

But the process flow diagram that natural landmark detection and touchdown area based on the pixel discrimination that the present invention proposes are determined method is as shown in Figure 2, and the implementation step is as follows:

Step 1: Image Acquisition

Video camera is installed in the below of lander, the image on acquisition ground that can be continuous in lander decline process.

Step 2: but the discrimination of calculating pixel point

If a pixel in the p presentation video, its coordinate is (px, py), and its pixel value is I (px, py), but then the discrimination of pixel p is the degree distinguished of other pixels in p and its neighborhood.If the neighborhood of pixel p is N _p, N _pBe a rectangle centered by pixel p, its length and width can be set according to actual conditions, if its length and width are set as width and the height of image, but then are the discriminations that carries out this pixel in whole sub-picture, and neighborhood N is set _pLength and width be respectively picture traverse and the height 1/3rd.Definition s (p, p ') be pixel p and pixel p ' similarity degree, herein, we adopt SSD to calculate the similarity degree of two pixels, and the SSD value is less, show that two pixels are more similar, the Size of Neighborhood that adopts when SSD is calculated in design is (2n+1) * (2m+1), then

$s(p,p^{\′})=\underset{i=-n}{\overset{n}{\mathrm{\Σ}}}\underset{j=-m}{\overset{m}{\mathrm{\Σ}}}{[I(\mathrm{px}+i,\mathrm{py}+j)-I(p^{\′}x+i,p^{\′}y+j)]}^2---\left(2\right)$

Wherein (px, py) is the coordinate of pixel p in image, and (p ' x, p ' are the coordinate of pixel p ' in image y).If p (s (p, p ')) expression pixel p and pixel p ' similar probability, then

$p\left(s(p,p^{\′})\right)=\frac{\exp \{-s(p,p^{\′})\}}{{\mathrm{\Σ}}_{p^{\′}\∈N_p}\exp \{-s(p,p^{\′})\}}---\left(3\right)$

But the discrimination of definition pixel be this pixel and the entropy of the interior similar probability distribution of pixel of its neighborhood, both

${\mathrm{distinguishbility}}_p=-{\mathrm{\Σ}}_{p^{\′}\∈N_p}p\left(s(p,p^{\′})\right)\log p\left(s(p,p^{\′})\right)---\left(4\right)$

For the pixel of mark among Fig. 1 calculate to its neighborhood in the similar probability distribution of pixel, as shown in Figure 3, can find out, be distributed with three kinds of situations:

1. spot distribution, shown in Fig. 3 (1-2), these pixels generally are the angle points in the image, the entropy of its similar probability distribution is less, but discrimination is high.

2. wire distributes, and shown in Fig. 3 (3-4), these pixels generally are the edges in the image, and the entropy of its similar probability distribution is placed in the middle, but discrimination is medium.

3. planar distribution, shown in Fig. 3 (5-7), these pixels generally belong to flat site, and the entropy of its similar probability distribution is larger, but discrimination is low.

Step 3: but but determine touchdown area based on the discrimination of pixel

Barrier region is all regarded in the zone that but we are high with discrimination and but the medium pixel of discrimination covers as, but but touchdown area is regarded in the zone that the low pixel of discrimination covers as.But touchdown area should satisfy following two requirements, the one, and area is enough large, so that lander lands; The 2nd, enough far away apart from barrier, to guarantee the safety of landing mission.Because the zone of image boundary outside is zone of ignorance, therefore desirable touchdown area should the range image border also enough far.Therefore but we also are set to height with the discrimination of the point on the image boundary, but both borderline point was also regarded the pixel that discrimination is high as.As shown in Figure 4, the some barrier region of redness among the figure, borderline point is also thought barrier region.But green portion is the low pixel of discrimination, can be used as touchdown area, and our target is to find the circle of a maximum, but so that this circle only comprises green area as touchdown area.Specific practice is the pixel of barrier region to be carried out morphological dilations at every turn, pixel around the barrier also is set to barrier region, such as Fig. 4 (b), (c), (d) shown in, can see, along with the carrying out of expanding, green area is more and more less, but the green area that reddens at last is exactly the center of circle of maximum touchdown area.Idiographic flow is:

1) successively the pixel in the barrier region (but pixel of height discrimination and medium discrimination) point is carried out morphological dilations, a pixel expands at every turn; Both the zone with a pixel around the barrier region also was set to barrier region.

2) but judge the number of the pixel that discrimination is low, if number greater than 1, then turns the first step; If number equals 1, then turned for the 3rd step, if number is 0, then turned for the 4th step.

3) if but the number of the low pixel of discrimination equals 1, then this pixel is the maximum round center of circle of can landing, but maximum can land radius of a circle can by calculate with the nearest expansion of this point before the height discrimination or the distance of the pixel of medium discrimination obtain, shown in Fig. 4 (d).

4) if but the number of the low pixel of discrimination equals 0, then choose before this time expansion, but but the low pixel of capped discrimination is as the center of circle of touchdown area, if any a plurality of such pixels, but then get the center of circle near a conduct touchdown area of picture centre, but radius can by calculate with the nearest expansion of this point before the height discrimination or the distance of the pixel of medium discrimination obtain.

Step 4: the natural landmark based on high discrimination pixel detects

Natural landmark refers in the environment existing, and unartificial setting, can be in order to references object or the pattern that identifies varying environment.Definition by natural landmark can find, but the pixel with height discrimination meets the definition of natural landmark, but the pixel that had both had a height discrimination can separate with the pixel region around it, can be used as natural landmark.But we with the set of the pixel with height discrimination in the certain radius as natural landmark.Because but the discrimination of these points is very high, therefore in follow-up image, can more guaranteedly trace into these pixels.

Claims (2)

1. but natural landmark and the touchdown area based on the pixel discrimination determined method, it is characterized in that: but a kind of natural landmark based on the pixel discrimination detects and touchdown area is determined method, and the specific implementation step is as follows:

Step 1: Image Acquisition

Video camera is installed in the below of lander, the image on acquisition ground that can be continuous in lander decline process;

Step 2: but the discrimination of the pixel in the image that calculation procedure one is obtained

If s (p, p ') be pixel p and pixel p ' similarity degree, establish p (s (p, p ')) expression pixel p and pixel p ' similar probability, but the discrimination of definition pixel is this pixel and the entropy of the interior similar probability distribution of pixel of its neighborhood, both

${\mathrm{distinguishbility}}_p=-{\mathrm{\Σ}}_{{p\′\∈N}_p}p\left(s(p,p\′)\right)\log p(s(p,p\′)$

N wherein _pNeighborhood for pixel p; Entropy is larger, but then discrimination is lower;

Step 3: but but the discrimination of the pixel that calculates based on step 2 is determined touchdown area

Barrier region is all regarded in zone but discrimination is high and that but the medium pixel of discrimination covers as, but but touchdown area is regarded in the zone that the low pixel of discrimination covers as; But also regard the point on the image boundary as pixel that discrimination is high, both also regarded barrier region as; The pixel of barrier region is carried out morphological dilations at every turn, pixel around the barrier also is set to barrier region, along with the carrying out of expanding, but touchdown area is more and more less, but but to be inflated at last the touchdown area that operation covers be exactly the center of circle of maximum touchdown area; But maximum can land radius of a circle can by calculate with the nearest expansion in the center of circle before the height discrimination or the distance of the pixel of medium discrimination obtain;

Step 4: carry out the natural landmark detection based on the high discrimination pixel that step 2 obtains

But the pixel with height discrimination can separate with the pixel region around it, meets the requirement as road sign, can be used as natural landmark; But we are natural landmark with the set of pixels cooperation with height discrimination in the certain radius.

2. but a kind of natural landmark and touchdown area based on the pixel discrimination as claimed in claim 1 determined method, it is characterized in that: can the land round center of circle and radius determining step of the maximum in the described step 2 is:

1) but be that the pixel of height discrimination and medium discrimination carries out morphological dilations to the pixel in the barrier region successively, a pixel expands at every turn; Both the zone with a pixel around the barrier region also was set to barrier region;

2) but judge the number of the pixel that discrimination is low, if number greater than 1, then turns the first step; If number equals 1, then turned for the 3rd step, if number is 0, then turned for the 4th step;

3) if but the number of the low pixel of discrimination equals 1, then this pixel is the maximum round center of circle of can landing, but maximum can be landed radius of a circle can by calculate with the nearest expansion of this point before the height discrimination or the distance of the pixel of medium discrimination obtain;

4) if but the number of the low pixel of discrimination equals 0, then choose before this time expansion, but but the low pixel of capped discrimination is as the center of circle of touchdown area, if any a plurality of such pixels, but then get the center of circle near a conduct touchdown area of picture centre, but radius can by calculate with the nearest expansion of this point before the height discrimination or the distance of the pixel of medium discrimination obtain.

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