CN111127542A - Image-based non-cooperative target docking ring extraction method - Google Patents
Image-based non-cooperative target docking ring extraction method Download PDFInfo
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Abstract
The invention provides an image-based non-cooperative target docking ring extraction method. Each butt-joint ring line segment has three attributes, length, width and brightness. The length represents the length range of the butt joint ring line segment, namely the length of the butt joint ring line segment; the width represents the width range of the butt joint ring line segment, namely the width of the butt joint ring line segment; the brightness represents the gray value of the butt-joint ring line segment. After the three attributes are set to a certain range of constraint values, only the butt joint ring line segment has the attribute, and the background area does not have the attribute, so that the butt joint ring line segment can be found by searching line segments meeting the three attributes. And finally, fitting the docking ring according to the found line segment. The method realizes high-precision identification of the docking ring under the condition of space complex illumination, and is favorable for subsequent rendezvous docking fuel filling and other work.
Description
Technical Field
The invention relates to a non-cooperative target docking ring extraction method based on a space target image, and belongs to the field of space image processing.
Background
During the process of approaching the non-cooperative target satellite, the space camera shoots the image of the docking ring of the non-cooperative target satellite, and then identifies the docking ring from the image. And the measurement of the relative position and the relative attitude of the target star can be completed according to the identified docking ring.
There have been some research efforts in recent years:
some methods are completed through deep learning, a program needs a large storage space, an existing hardware platform is limited in storage space and cannot complete storage, and the internal principle of the program is not completely transparent and has failure probability, so that the method cannot be accepted in space application.
Some methods compute the docking ring circle from the formed trajectory by continuously collecting the targets. The required acquisition time is long, and the real-time requirement is difficult to meet.
In some methods, edges are detected through operators, then the edges are extracted and classified, and finally circle detection is carried out. The method has the advantages of complex flow and high calculation amount, and is difficult to extract the target circle in the conventional hardware platform and in the set time.
Some methods perform circle extraction of the docking ring by improving a circle transformation algorithm, but the method has high complexity, is difficult to operate in a hardware platform with low space computing capability, and has low accuracy under the condition of space complex illumination.
By using the circle detection method, it is found to be difficult to complete the image recognition of the docking ring in a spatial environment. Firstly, the interference of space imaging stray light is serious, the polyimide on the surface of a star body reflects sunlight, different high-brightness areas are formed on the surface, and a complex background with uneven brightness is formed; secondly, the docking rings are not completely highlighted, some areas are darker, and some areas are bright but have uneven brightness, as shown in fig. 2, and due to the factors, the traditional method is difficult to identify the space non-cooperative target docking ring; finally, in rendezvous and docking, 10 images are required to be processed every second, 10 attitude information is calculated, and under a low-computing-capability platform, the algorithm complexity is required to be very low, as shown in fig. 2.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method comprises the steps of dividing the butt joint ring into different line segments, wherein each butt joint ring line segment has three attributes, namely length, width and brightness, searching the butt joint ring line segments from different directions according to the attributes of the butt joint ring line segments, fitting the whole butt joint ring after finding the butt joint ring line segments, and testing and calculating the butt joint ring with high speed, high robustness and high precision.
The purpose of the invention is realized by the following technical scheme: a non-cooperative target docking ring extraction method based on images sequentially comprises the following steps:
the method comprises the steps that firstly, a space camera shoots an image of a non-cooperative target satellite, an O-XY two-dimensional orthogonal coordinate system is established, the horizontal right direction is the positive direction of an x axis, the vertical upward direction is the positive direction of a y axis, the x axis and the y axis are located in a plane where the whole image is located, and the lower left corner of the image is a coordinate origin (0, 0). Calculating brightness in image greater than brightness threshold T1The average value (x0, y0) of the x coordinate and the y coordinate of the pixel is obtained based on the x coordinate value and the y coordinate value of the pixel.
Setting an outward radiation direction by taking (x0, y0) as a starting point, wherein the radiation interval between two adjacent radiation directions is D degrees;
step three, in each outward radiation direction, except the radiation lines passing through the starting point (x0, y0), two parallel lines are symmetrically arranged on two sides of each radiation line respectively to serve as auxiliary lines for assisting in finding the butt joint ring, each radiation line and the two corresponding auxiliary lines form three parallel lines, the three parallel lines are adopted to extend along the radiation direction to find the butt joint ring, and the distance between the two symmetrically arranged auxiliary lines is M pixels; m is the length of the butt-joint loop segment to be searched. (the butt-joint ring is a circle composed of a plurality of line segments)
Step four, in an outward radiation direction, when a certain pixel is found along the radiation line, judging whether the brightness of the pixel is greater than a brightness threshold value T or not2Simultaneously judging whether the pixel brightness in the set area on the left and right auxiliary lines of the radiation line in the radiation direction is also larger than a brightness threshold value T2If yes, the inner edge of the butting ring is judged to be found, the step five is carried out, otherwise, the three parallel lines, namely the radial line and the auxiliary line, continue to be searched along the radiation direction until the set length range is searched, and the search is stopped. (Here T2Corresponding to the brightness attribute of the butt joint ring line segment. )
Step five, continuously searching along the radiation direction, and if the brightness is greater than the brightness threshold value T in the step four2After the pixel position is advanced by N pixels, whether the brightness is less than T is judged2Whether the brightness of the pixels in the set area on the left auxiliary line and the right auxiliary line is less than T or not is judged simultaneously2If the conditions are met, the suspected outer edge of the docking ring is found, and the docking ring is found to be finished; otherwise, the three parallel lines, namely the radiation line and the auxiliary line, continue to be searched along the radiation direction until the set length range is searched, and stopping searching. (where N corresponds to the Butt Loop segment Width attribute.)
And step six, after the butt joint ring in one radiation direction is searched, searching the butt joint ring in the next radiation direction until all radiation directions are searched, and fitting the inner edge point and the outer edge point of the searched butt joint ring according to each radiation direction to obtain the butt joint ring.
Preferably, the method for calculating the radiation interval D degree between two adjacent radiation directions in the second step includes: the value of D can be adjusted between 10 degrees and 45 degrees, D is an adjustable parameter, if D is 45 degrees, 8 radiation directions are shown, namely 8 butt joint ring line segments are searched in 8 radiation directions.
Preferably, the starting points of the three parallel lines in the third step are respectively: the middle line, i.e. the radiation starting point, is (x0, y 0); the starting points of the other two lines, i.e., the two auxiliary lines, are (x0, y0) shifted by M/2 pixels toward both sides in the direction perpendicular to the radial line.
Preferably, in the fourth step, it is determined whether or not the luminance of the pixel in the setting area on the left and right auxiliary lines of the radiation line in the radiation direction is also larger than the luminance threshold T2The judging method comprises the following steps: when the radiation travels to a brightness greater than a threshold T2Recording the distance S1 from the starting point (x0, y0) of the radiation line to the pixel (i.e., the pixel), and determining whether the brightness of the left and right auxiliary lines is greater than the threshold T in the region from the starting point S1-r to S1+ r2The pixel of (2).
Preferably, in the fifth step, whether the brightness of the pixel points on the left and right auxiliary lines in the set area is less than T is judged2The judging method comprises the following steps: when the radiation line continues to travel until the brightness is less than the threshold T2When the pixel (2) is recorded, the distance S2 from the starting point (x0, y0) to the position (i.e., the pixel) of the radiation line is recorded, and whether the brightness of the left and right auxiliary lines is less than the threshold T in the region from the starting point S2-r to the starting point S2+ r is determined2The pixel of (2).
Preferably, in the method for determining the inner edge and the outer edge of the docking ring in the sixth step, the inner edge points are as follows: the three parallel lines in the fourth step all have the brightness larger than the threshold value T in a certain area2Along the radiation direction, the brightness of three lines is greater than T2The first pixel of (2) is the inner edge point of the docking ring respectively; its outer edge points are: after the radiation line continues to advance by N pixels in the step five, if the brightness of all three parallel lines in a certain area is less than the threshold value T2Along the radiation direction, the brightness of three lines is less than T2The first pixels of (a) are the outer edge points of the docking ring respectively.
Preferably, the non-cooperative target is a satellite, the requirement for shooting the image of the non-cooperative target is that when the satellite of one party carries a space camera and approaches to the direction of the docking ring of the non-cooperative target satellite within 100 meters, the space camera shoots the docking ring of the non-cooperative target satellite, at the moment, the satellite of one party completes the docking ring identification work according to the docking ring image shot by the space camera, the relative position and the posture of the non-cooperative target satellite can be calculated according to the identified docking ring, and then the non-cooperative target satellite approaches to capture or fill space fuel.
Preferably, M is the length of the searched butt-joint loop line segment and corresponds to the butt-joint loop line segment length attribute.
Preferably, N is the searched docking circle segment width, corresponding to the docking circle segment width attribute.
Preferably, T2And corresponding to the brightness attribute of the butt joint ring line segment for the searched butt joint ring line segment brightness.
Preferably, T1And extracting the brightness threshold of the non-cooperative target satellite from the image.
Compared with the prior art, the invention has the following beneficial effects:
(1) the invention decomposes the target docking ring into different docking ring segments and identifies the different docking ring segments. As the identification of the butt joint rings is simplified into the identification of different butt joint ring line segments, the complex problem is simplified, and a method for rapidly solving the problem is found.
(2) The invention extracts three unique attributes of the butt joint ring line segment. Different line segments are summarized into three attributes of length, width and brightness, and the attributes are only possessed by the butt-joint ring, and the background does not simultaneously satisfy the areas of certain length, width and brightness, so that the searched target characteristics are further simplified and unique. In a complex bright and dark background, three attributes are satisfied, namely, the three attributes are a section of the docking ring, the precision is high, the robustness is strong, and the docking ring can be found under a high and complex background through testing.
(3) In the process of finding the butt joint ring line segment, the invention further simplifies the calculation process by finding three parallel lines, and has high operation efficiency.
(4) In the invention, the circle center of the butt joint ring can be fitted only by identifying 3 line segments. The robustness is high.
(5) The method has the advantages of no complex comparison and screening, high speed and suitability for the operation of the space embedded platform.
(6) The method has wide applicability, and the algorithm steps of three, four and five are adjustedM T (g)2N parameter value, namely adjusting and searching length, brightness and width parameters of a section of the butt joint ring, and finding the butt joint ring meeting different width and brightness characteristics. Only the parameters need to be adjusted to meet the requirements of different butt joint rings.
Drawings
FIG. 1 is a flow chart of the steps of the present invention;
FIG. 2 is a schematic view of a spatial non-cooperative target docking collar;
FIG. 3 is a fragmentary schematic view of the docking collar;
FIG. 4 is a schematic diagram of the preferred 8 radiation directions of the present invention;
FIG. 5 is a schematic view of the starting point position of the present invention;
FIG. 6 is a schematic diagram of the present invention for finding other orientation docking rings.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
The invention provides an image-based non-cooperative target docking ring extraction method. Each butt-joint ring line segment has three attributes, length, width and brightness. The length represents the length range of the butt joint ring line segment, namely the length of the butt joint ring line segment; the width represents the width range of the butt joint ring line segment, namely the width of the butt joint ring line segment; the brightness represents the gray value of the butt-joint ring line segment. After the three attributes are set to a certain range of constraint values, only the butt joint ring line segment has the attribute, and the background area does not have the attribute, so that the butt joint ring line segment can be found by searching line segments meeting the three attributes. And finally, fitting the docking ring according to the found line segment. The method realizes high-precision identification of the docking ring under the condition of space complex illumination, and is favorable for subsequent rendezvous docking fuel filling and other work.
When finding the identification method, it is found that the extraction of the docking ring in fig. 2 may be changed to the extraction of different docking ring segments in the docking ring. As shown in fig. 3, the docking ring is divided into white docking ring segments at different positions, the length and number of the white docking ring segments can be set by themselves, and 8 segments are taken as an example in the following figure. Further, 16, 32 segments, etc. can be expanded to different locations, if desired.
Each butt-joint ring line segment has three attributes, length, width and brightness. The length represents the length range of the butt joint ring line segment, namely the length of the butt joint ring segment; the width represents the width range of the butt joint ring line segment, namely the width of the butt joint ring of the segment; the brightness represents the size of the gray value of the butt-joint ring line segment. The three attributes can represent a section of the docking ring, and after the three attributes are set to a certain range of constraint values, only the docking ring line segment has the attributes, and the background area does not have the attributes, so that the docking ring line segment can be found by searching the line segment meeting the three attributes.
In the implementation process of the invention, the aim of rapidly identifying the docking ring can be achieved on the embedded platform, and tests show that the method has the advantages of high precision, high speed, strong robustness and wide practicability.
After the space non-cooperative target satellite works for several years, the space non-cooperative target satellite needs to be captured and refueled for prolonging the working time due to fuel exhaustion. In the satellite capturing process, one very obvious characteristic of a non-cooperative target satellite is a docking ring, and if the docking ring can be identified, the circle center of the docking ring is the position of the filling port. The filling port is only identified, because the target is too small, the identification is very difficult, and particularly under the long distance, the identification is difficult to directly complete. Thus, by identifying the docking ring, the filler neck is found. The identification of the docking collar becomes very critical.
The space has no atmosphere, and sunlight directly irradiates the butt joint ring and then is scattered for many times, so that the butt joint ring and the star body are uneven in brightness and darkness, and high-brightness and high-dark areas exist. The existing docking ring or circle extraction algorithm is tested, and the method is difficult to apply in a space environment. And the space computer has low computational efficiency, the storage space allocated to the docking ring identification program is small, but the task itself needs 10Hz computing power, namely the processing of 10 images is completed every second, and the existing docking ring or circle extraction algorithm is difficult to meet the task requirements in the aspects of operating speed and storage space.
Aiming at the imaging of a space target, the invention provides a docking ring extraction method, which has low complexity and high precision and meets the task requirements through practical verification.
As shown in fig. 1, the method for extracting an image-based non-cooperative target docking ring according to the present invention preferably includes the following steps:
shooting an image of a non-cooperative target, establishing an O-XY two-dimensional orthogonal coordinate system, defining that the horizontal right direction is the positive direction of an x axis, the vertical upward direction is the positive direction of a y axis, the x axis and the y axis are positioned in a plane where the whole image is positioned, the lower left corner of the image is a coordinate origin (0, 0), and calculating that the brightness in the image is greater than a brightness threshold T1The average value (x0, y0) of the x coordinate and the y coordinate of the pixel is obtained, specifically:
the space camera is arranged in front of the satellite of the space camera and is opposite to the non-cooperative target satellite docking ring in the process of approaching the non-cooperative target satellite. The space camera shoots an image of a non-cooperative target satellite, an O-XY two-dimensional orthogonal coordinate system is established, the horizontal right direction is the positive direction of an x axis, the vertical upward direction is the positive direction of a y axis, the x axis and the y axis are positioned in a plane where the whole image is positioned, and the lower left corner of the image is a coordinate origin (0, 0). Calculating brightness in image greater than brightness threshold T1Is statistically greater than a luminance threshold value T1The x-coordinate and the y-coordinate values of the pixel (2) of (4) are obtained, and the average value of the coordinate values of the pixel (x0, y0) between the x-coordinate and the y-coordinate is obtained.
Luminance in the calculated image is greater than a luminance threshold T1In the pixel process, the gray level mean value v of all pixels in the image is obtainedmeanMaximum gray value v in the imagemaxAnd minimum gray value v in imagemin. Wherein v ismaxThe preferred value satisfies two conditions, one is that 10 or more pixels are larger than the pixel value, and the other is that the maximum value is selected from the pixels satisfying the condition one; v. ofminThe value also needs to satisfy two conditions, one is that 10 or more pixels are less than or equal to the pixel value, and the other is that the minimum value is selected from the pixels satisfying the condition one. Thus, the maximum value and the minimum value are taken to prevent noise points from interfering with calculation.
T of luminance threshold1The calculation method is preferably
I.e. maximum gray value vmaxMinus the minimum gray value vminAfter taking one half of the difference value of (c), the average value v of the gray levels of all the pixels is obtainedmeanThe absolute value of the difference is calculated by the mean value v of the gray levels of all pixelsmeanThe absolute value is subtracted to obtain a value.
Step two, setting an outward radiation direction by taking (x0, y0) as a center, wherein the radiation interval between two adjacent radiation directions is D degrees, and preferably:
and the first image is subjected to initial capture mode image processing. The second image starts and a tracking mode image processing is performed.
In the initial capture mode image processing, a preferred method for determining the radiation interval D is:
the radiation interval D between two adjacent radiation directions is set to be 120 degrees initially, and then three radiation directions are shared. Preferably: the first radial direction is from (x0, y0) in the horizontal right direction, i.e., at an angle of 0 degrees to the x-axis; the second radial direction is from (x0, y0) and is at 120 degree angle to the first radial direction counterclockwise; the second radial direction is from (x0, y0) and is at an angle of 240 degrees counterclockwise from the first radial direction. The butt-joint loop segment is looked up in these three radiation directions.
The further preferable scheme is as follows: if only one radiation direction finds the butt joint ring line segment, the radiation direction is taken as the starting direction, the radiation direction is moved along the anticlockwise direction by taking D/4 degrees as the step length, the search is carried out in each radiation direction until H butt joint ring line segments are found, and the search is finished. If H butt joint ring line segments are not found after one circle of search, the step length is reduced by half, namely D/8 degrees, and the search is carried out in each radiation direction; if not found, the moving interval is reduced by half, namely D/16 degrees, until H butt-joint ring line segments are found.
The further preferable scheme is as follows: if only two radiation directions find the butt joint ring line segments, the center line of an included angle of the two radiation directions is used as an initial direction, the movement is carried out along the anticlockwise direction by taking D/4 degrees as a step length, the radiation direction is changed, the search is carried out in each radiation direction until H butt joint ring line segments are found, and the search is finished. If the butt joint ring line segment is not found after the search for one circle, the step length is reduced by half, namely D/8 degrees, and the search is carried out in each radiation direction; if not found, the moving interval is reduced by half, namely D/16 degrees, until H butt-joint ring line segments are found.
The further preferable scheme is as follows: if the three radiation directions all find the butt joint ring line segment, or if the three radiation directions do not find the butt joint ring line segment, the first radial line direction is taken as the starting direction, the radiation direction is changed by moving counterclockwise by taking D/4 degrees as the step length, the search is carried out in each radiation direction until H butt joint ring line segments are found, and the search is finished. If H butt joint ring line segments are not found after one circle of search, the step length is reduced by half, namely D/8 degrees, and the search is carried out in each radiation direction; if not found, the moving interval is reduced by half, namely D/16 degrees, until H butt-joint ring line segments are found.
In the tracking mode image processing, a preferable determination method of the radiation interval D is:
and searching the butt joint ring line segment in the image according to the radiation direction of the butt joint ring line segment found in the previous image. The preferred scheme is as follows: and if the number of the searched butt joint ring line segments is equal to H, finishing the search. If the number of the searched butt joint ring line segments is less than H, the radiation direction is changed by taking the radiation line direction of the first butt joint ring line segment found in the image as the starting direction, preferably moving counterclockwise by taking D/4 degrees as the step length, searching in each radiation direction until the H butt joint ring line segments are found, and finishing the searching. The further preferable scheme is as follows: if H butt joint ring line segments are not found after one circle of search, the step length is reduced by half, namely D/8 degrees, and the search is carried out in each radiation direction; if not found, the moving interval is reduced by half, namely D/16 degrees, until H butt-joint ring line segments are found.
H is a set parameter, preferably greater than 3.
Step three, in each outward radiation direction, taking each radiation line as a center except the radiation line passing through the center (x0, y0), respectively and symmetrically arranging two parallel lines as auxiliary lines for assisting in finding the butt joint ring, wherein each radiation line and the two corresponding auxiliary lines form three parallel lines, the three parallel lines are adopted to extend along the radiation direction to find the butt joint ring, the distance between the two symmetrically arranged auxiliary lines is M pixels, and the distance between each auxiliary line and the radiation line is M/2; m is the length of the butt joint ring line segment needing to be searched, and specifically comprises the following steps:
and the first image is subjected to initial capture mode image processing. The second image starts and a tracking mode image processing is performed.
In the initial capture mode image processing, M is a given value.
In the tracking mode image processing, M is automatically adjusted. The M automatic adjustment process is preferably:
if a certain radiation direction finds the butt joint ring line segment, the radiation line and the two auxiliary lines in the radiation direction respectively form a line segment from the inner edge to the outer edge of the butt joint ring along the finding direction, and the line segments are respectively marked as a radiation line segment, an auxiliary line segment 1 and an auxiliary line segment 2. The gray average values of the three line segments are respectively marked as v0、v1、v2. The value of the radiation direction M of the current image is preferably
Where k is a coefficient, MpThe distance between the two auxiliary lines of the radiation direction of the previous image; v. of0、v1、v2In the upper image, the radiation line and the two auxiliary lines form the gray average value of the radiation line segment, the auxiliary line segment 1 and the auxiliary line segment 2 from the inner edge to the outer edge of the butt-joint ring in the radiation direction.
If the radiation direction does not find the docking looping segment in the upper image or does not query the docking looping segment, M preferably adopts the most recently calculated value.
Step four, in an outward radiation direction, when a certain pixel is found along the radiation line, the brightness of the pixel is found to be larger than the set background brightness threshold value T2Judging whether the brightness of the pixels in the set area on the left and right auxiliary lines of the radiation line in the radiation direction is larger than the set background brightness threshold value T2If yes, judging that the inner edge of the butting ring is suspected to be found, turning to the fifth step, otherwise, continuously searching three parallel lines, namely the radial line and the auxiliary line along the radiation direction until the set length range L is searched1And stopping searching.
And the first image is subjected to initial capture mode image processing. The second image starts and a tracking mode image processing is performed.
Luminance threshold value T in initial capture mode image processing2Is preferably calculated by
T2＝T1+t
Wherein T is1Preferably, the central threshold is calculated in step one, and t is a given parameter.
In tracking mode image processing, the brightness threshold T2Is preferably calculated by
In the above formula v0、v1、v2The calculation method is the same as the third step; if the radiation direction does not find the docking ring in the upper image, T2The most recently calculated values are used.
Length L in initial capture mode image processing1Is a given value.
Length L in tracking mode image processing1Is preferably calculated by
L1＝max{l1,l2,...,li}+ld
Wherein l1,l2,...,liThe length value from the starting point of the radial to the edge point of the outer side of the butt joint ring in the butt joint ring line segment found in the previous image is obtained; ldGiven the parameters.
The starting point of the radiation is (x0, y 0). Starting points of the two auxiliary lines are calculated by moving the falling points by M/2 in two directions perpendicular to the radial lines from (x0, y0), which are starting points of the two radial lines. The radial line and the two auxiliary lines search the butt-joint ring line segment from the respective starting points along the direction parallel to the radial line.
Step five, continuously searching along the radiation direction, and if the brightness is greater than the brightness threshold value T in the step four2After the pixel position is advanced by N pixels, whether the brightness is less than T is judged2Whether the brightness of the pixels in the set area on the left auxiliary line and the right auxiliary line is less than T or not is judged simultaneously2If the conditions are met, the suspected outer edge of the docking ring is found, and the docking ring is found to be finished; otherwise, the three parallel lines, namely the radiation line and the auxiliary line, continue to be searched along the radiation direction until the set length range is searched, and stopping searching. Where N corresponds to the butt-joint loop segment width attribute.
In the initial capture mode image processing, the advance pixel N is a given value.
In the tracking mode image processing, the calculation method of the advance pixel N is preferably,
N＝min{n1,n2,...,ni}-nd
wherein n is1,n2,...,niIn the upper image, the distance n between the inner edge point and the outer edge point of the butt-joint ring is found along the radial linedGiven the parameters.
And step six, after the butt joint ring line segment in one direction is searched, searching the butt joint ring line segment in the next direction until all directions are searched, and fitting the inner edge point and the outer edge point of the butt joint ring line segment searched according to all the outward radiation directions to form the butt joint ring.
The further scheme for improving the extraction precision of the invention comprises the following steps:
in step three, in the tracking mode, M is automatically adjusted according to the calculation condition of the previous image. In the tracking mode, the M value of the current radiation direction is preferably:
whereinliThe distance from the starting point to the inner edge of the butting ring of the radial line in the radiation direction for the upper image; f. ofi 1、fi 2The distance from the respective starting point to the inner edge of the butt joint ring is obtained by the two auxiliary lines in the radiation direction for the upper image; l fi 1-liThe absolute value of the difference between the distance from the starting point to the inner edge of the butt joint ring of one auxiliary line in the radiation direction of the upper image and the distance from the starting point to the inner edge of the butt joint ring of the radiation line is | shown; l fi 2-liThe absolute value of the difference between the distance from the starting point to the inner edge of the butting ring of the other auxiliary line in the radiation direction of the upper image and the distance from the starting point to the inner edge of the butting ring of the radial line is | shown; mpThe distance between the two auxiliary lines of the radiation direction of the previous image; v. of0、v1、v2In the upper image, in the radiation direction, the radiation line and the two auxiliary lines form a radiation line segment, an auxiliary line segment 1 and an auxiliary line segment 2 from the inner edge to the outer edge of the butt-joint ring; i. j, k are coefficients.
The invention further prefers to improve the extraction speed as follows:
in the second step, the tracking mode image processing method started by the second image comprises the following steps:
each found butt joint ring line segment in the upper image, the radiation line and the two auxiliary lines in the radiation direction form a line segment from the inner edge to the outer edge of the butt joint ring, and the line segments are respectively marked as a radiation line segment, an auxiliary line segment 1 and an auxiliary line segment 2. The gray average values of the three line segments are respectively marked as v0、v1、v2. Calculating v0、v1、v2Mean value of gray level and threshold value T of background gray level1Preferably, the difference calculation formula is as follows
Then, the difference sum of the distance from the starting point to the inner edge of the butting ring of the two auxiliary lines in the radiation direction in the upper image and the distance from the starting point to the inner edge of the butting ring of the radiation direction in the upper image is calculated, and the calculation formula is preferably as follows
|fi 1-li|+|fi 2-li|
The above two factors are weighted to determine the degree of superiority of the radiation direction in the previous image, and the calculation formula of the degree of superiority is preferably as follows
In the previous image, the radiation directions of all the searched butt joint ring line segments are sorted according to the above formula, and the three radiation directions in the front of the sorting are taken as the three radiation directions of the searched butt joint ring of the current image. And if the docking ring line segment is found in all three directions of the current image, the finding is finished. If three butt joint ring line segments cannot be found in the three directions of the current image, the traditional method is recovered, the radiation line direction of the first butt joint ring line segment found in the current image is taken as the starting direction, the image moves along the anticlockwise direction by taking D/4 degrees as the step length, the radiation direction is changed, the image is searched in each radiation direction until H butt joint ring line segments are found, and the search is finished. If H butt joint ring line segments are not found after one circle of search, the step length is reduced by half, namely D/8 degrees, and the search is carried out in each radiation direction; if not found, the moving interval is reduced by half, namely D/16 degrees, until H butt-joint ring line segments are found.
The further preferable scheme for realizing the improvement of the extraction stability comprises the following steps:
in step four, in the tracking mode, the radial line and the left and right auxiliary lines have respective brightness thresholds, and the brightness threshold of the radial line
And the brightness threshold of the left and right auxiliary lines
Is preferably calculated by
In the image-based non-cooperative target docking ring extraction method of the present invention, a further preferred extraction scheme is as follows:
the first image, the preferred scheme for performing the initial capture mode calculation is as follows:
and (1) in the whole image, the horizontal right direction is the positive direction of an x coordinate, the vertical upward direction is the positive direction of a y coordinate, and the lower left corner of the image is the origin of coordinates (0, 0). And calculating pixels with brightness larger than a certain threshold value, and solving the mean value (x0, y0) of the pixel values in xy coordinates.
And (2) taking (x0, y0) as a center, and radiating outwards to search the docking ring. Each radiation is spaced D degrees apart. D is parameter adjustable, D is preferably 45 degrees, then 8 radiations exist, namely 8 butt joint ring line segments are searched in 8 directions. The 8 radiation directions are shown in fig. 4.
And (3) adopting three parallel lines in each radiation direction, extending and searching, wherein the three parallel lines are respectively a middle radiation line and a left auxiliary line and a right auxiliary line. The left auxiliary line and the right auxiliary line, namely the two outermost parallel lines, are spaced by 16 pixels, and 16 is the length of the searched butt joint ring line segment and corresponds to the length attribute. The starting points of the three parallel lines are respectively: the starting point of the radiation is (x0, y 0); the starting points of the other two auxiliary lines are respectively (x0, y0) shifted by 8 pixels to both sides along the direction perpendicular to the radiation direction of the middle line. As shown in fig. 5, the starting point when searching for a direction docking loop is shown, where the white dot is the starting point of the middle line, and the two white circles are the starting points of the two auxiliary lines. Where M preferably takes the value 16.
In step (4), preferably, when the radiation line travels to a pixel having a luminance greater than the luminance threshold value 120, the distance 260 from the starting point to the middle radiation line is recorded, and it is determined whether or not there is a point having a luminance greater than the luminance threshold value 120 in the region from the starting point 240 to 280 between the left and right auxiliary lines. If yes, the inner edge of the butting ring is considered to be found, the step five is carried out, otherwise, the search is continued until the search line meets the length 400. Here 120 corresponds to the line segment brightness attribute, i.e., the brightness attribute of the docking ring.
And (5) continuing to advance the intermediate radiation line by 50 pixels, recording the distance 300 from the starting point to the intermediate radiation line when the intermediate radiation line continues to advance to the pixels with the brightness smaller than the threshold value 120, and judging whether the brightness of the left and right auxiliary lines is smaller than the background brightness mean value 120 in the area from the starting point to the area from 280 to 320. If so, the site is considered to be a docking ring.
And (6) after the butt joint ring in one direction is searched, searching the butt joint ring in the next direction until all the set directions are searched. The diagram of finding the docking ring in the other direction is shown in fig. 6.
And starting a second image, and performing tracking mode calculation, wherein the calculation process comprises the following steps:
and (1) in the whole image, the horizontal right direction is the positive direction of an x coordinate, the vertical upward direction is the positive direction of a y coordinate, and the lower left corner of the image is the origin of coordinates (0, 0). And calculating pixels with brightness larger than a certain threshold value, and solving the mean value (x0, y0) of the pixel values in xy coordinates.
And (2) taking (x0, y0) as a center, and radiating outwards to search the docking ring. And in each radiation direction in the upper image, the radiation lines on the docking rings and the difference value between the gray level mean value of the two auxiliary lines and the background gray level threshold value are sorted according to the difference value, and the first three radiation directions with the largest difference value are taken as the three directions for initial search of the current image. The three directions are respectively 90 degrees anticlockwise and 225 degrees anticlockwise along the x-axis 0 degree direction and the x-axis 0 degree direction, and searching is carried out along the three radiation directions respectively.
And (3) adopting three parallel lines in each radiation direction, extending and searching, wherein the three parallel lines are respectively a middle line and two auxiliary lines. The M values for the three radiation directions are calculated as 15, 16, 14, respectively, i.e. the outermost two parallel lines of the three radiation directions are spaced apart by 15, 16, 14, respectively. The starting points of the three parallel lines are respectively: the starting point of the radiation is (x0, y 0); the starting points of the other two auxiliary lines are respectively (x0, y0) shifted by M/2 along the direction perpendicular to the radial line.
And (4) taking one radiation direction, and calculating a brightness threshold value as 125. When the middle radial line travels to a pixel with the brightness larger than 125, the distance 265 from the starting point to the middle radial line is recorded, and whether points with the brightness larger than the brightness threshold value 125 exist in the areas 245 to 285 from the starting point of the left auxiliary line and the right auxiliary line is judged. If yes, the inner edge of the butting ring is considered to be found, the step five is carried out, otherwise, the search is continued until the search line meets the length range 400. Here 125 corresponds to the line segment brightness attribute, i.e. the brightness attribute of the docking ring.
And (5) continuing to advance the intermediate radiation line by 50 pixels, recording the distance 306 from the starting point to the intermediate radiation line when the intermediate radiation line continues to advance to the pixels with the brightness smaller than the brightness threshold value 125, and judging whether points with the brightness smaller than the background brightness threshold value 125 exist in the areas from the starting points 286 to 326 of the left and right auxiliary lines. If so, the site is considered to be a docking ring.
And (6) after the butt joint ring in one radiation direction is searched, searching the butt joint ring in the next radiation direction until the search of the three radiation directions is completed.
Tests in the scheme show that the method has high precision in extracting the docking ring, and the error is within 5mm after 10 times of testing on the precision of extracting the docking ring, which is specifically shown in the following table 1. This precision completion can meet rendezvous and docking requirements.
TABLE 1 Tab-Loop extraction error Table
The 10 docking ring extraction speed tests found that all calculations were completed within 60ms, as shown in table 2 below. This speed is done to meet the rendezvous and docking requirements.
Table 2 docking ring extraction speedometer
The invention decomposes the target docking ring into different docking ring segments and identifies the different docking ring segments. As the identification of the butt joint rings is simplified into the identification of different butt joint ring line segments, the complex problem is simplified, and a method for rapidly solving the problem is found. The invention extracts three unique attributes of the butt joint ring line segment. Different line segments are summarized into three attributes of length, width and brightness, and the attributes are only possessed by the butt-joint ring, and the background does not simultaneously satisfy the areas of certain length, width and brightness, so that the searched target characteristics are further simplified and unique. In a complex bright and dark background, three attributes are satisfied, namely, the three attributes are a section of the docking ring, the precision is high, the robustness is strong, and the docking ring can be found under a high and complex background through testing.
In the process of finding the segment of the butt joint ring, the invention further simplifies the calculation process by finding three parallel lines, has high operation efficiency, and can fit the circle center of the butt joint ring by only identifying 3 segments. The method has the advantages of high robustness, no complex comparison and screening, high speed and suitability for space embedded platform operation.
The method has wide applicability, and M T in the third, fourth and fifth steps of the algorithm is adjusted2N parameter value, namely adjusting and searching length, brightness and width parameters of a section of the butt joint ring, and finding the butt joint ring meeting different width and brightness characteristics. Only the parameters need to be adjusted to meet the requirements of different butt joint rings.
Those skilled in the art will appreciate that those matters not described in detail in the present specification are well known in the art.
Claims (10)
1. A non-cooperative target docking ring extraction method based on images is characterized in that: the method comprises the following steps:
the method comprises the following steps that firstly, a space camera shoots an image of a non-cooperative target satellite, an O-XY two-dimensional orthogonal coordinate system is established, the horizontal right direction is the positive direction of an x axis, the vertical upward direction is the positive direction of a y axis, the x axis and the y axis are located in a plane where the whole image is located, and the lower left corner of the image is a coordinate origin (0, 0); calculating brightness in image greater than brightness threshold T1The pixel of (2) calculating the mean value (x0, y0) of the x coordinate and the y coordinate of the pixel based on the x coordinate value and the y coordinate value of the pixel;
setting an outward radiation direction by taking (x0, y0) as a starting point, wherein the radiation interval between two adjacent radiation directions is D degrees;
step three, in each outward radiation direction, except the radiation lines passing through the starting point (x0, y0), two parallel lines are symmetrically arranged on two sides of each radiation line respectively to serve as auxiliary lines for assisting in finding the butt joint ring, each radiation line and the two corresponding auxiliary lines form three parallel lines, the three parallel lines are adopted to extend along the radiation direction to find the butt joint ring, and the distance between the two symmetrically arranged auxiliary lines is M pixels; m is the length of the butt joint ring line segment to be searched;
step four, in an outward radiation direction, when a certain pixel is found along the radiation line, judging whether the brightness of the pixel is greater than a brightness threshold value T or not2Simultaneously judging whether the pixel brightness in the set area on the left and right auxiliary lines of the radiation line in the radiation direction is also larger than a brightness threshold value T2If yes, judging that the inner edge of the butting ring is suspected to be found, turning to the fifth step, otherwise, continuously searching three parallel lines, namely the radial line and the auxiliary line along the radiation direction until the set length range is searched, and stopping searching;
step five, continuously searching along the radiation direction, and if the brightness is greater than the brightness threshold value T in the step four2After the pixel position is advanced by N pixels, whether the brightness is less than T is judged2Whether the brightness of the pixels in the set area on the left auxiliary line and the right auxiliary line is less than T or not is judged simultaneously2If the conditions are met, the suspected outer edge of the docking ring is found, and the docking ring is found to be finished; otherwise, the three parallel lines, namely the radiation line and the auxiliary line, continue to be searched along the radiation direction until the set length range is searched, and stopping searching;
and step six, after the butt joint ring in one radiation direction is searched, searching the butt joint ring in the next radiation direction until all radiation directions are searched, and fitting the inner edge point and the outer edge point of the searched butt joint ring according to each radiation direction to obtain the butt joint ring.
2. The image-based non-cooperative target docking ring extraction method according to claim 1, wherein: the calculation method of the radiation interval D degree between two adjacent radiation directions in the second step comprises the following steps: the value of D can be adjusted between 10 degrees and 45 degrees, D is an adjustable parameter, if D is 45 degrees, 8 radiation directions are shown, namely 8 butt joint ring line segments are searched in 8 radiation directions.
3. The image-based non-cooperative target docking ring extraction method according to claim 1, wherein: and M is the length of the searched butt joint ring line segment and corresponds to the length attribute of the butt joint ring line segment.
4. The image-based non-cooperative target docking ring extraction method according to claim 1, wherein: the starting points of the three parallel lines in the third step are respectively as follows: the middle line, i.e. the radiation starting point, is (x0, y 0); the starting points of the other two lines, i.e., the two auxiliary lines, are (x0, y0) shifted by M/2 pixels toward both sides in the direction perpendicular to the radial line.
5. The image-based non-cooperative target docking ring extraction method according to claim 1, wherein: and N is the width of the searched butt joint ring line segment and corresponds to the property of the width of the butt joint ring line segment.
6. The image-based non-cooperative target docking ring extraction method according to claim 1, wherein: in the fourth step, it is determined whether the brightness of the pixel in the set area on the left and right auxiliary lines of the radiation line in the radiation direction is also greater than the brightness threshold T2The judging method comprises the following steps: when the radiation travels to a brightness greater than a threshold T2Recording the distance S1 from the starting point (x0, y0) of the radiation line to the pixel (i.e., the pixel), and determining whether the brightness of the left and right auxiliary lines is greater than the threshold T in the region from the starting point S1-r to S1+ r2The pixel of (2).
7. An image-based non-cooperative target docking ring extraction as defined in claim 1The method is characterized in that: t is2And corresponding to the brightness attribute of the butt joint ring line segment for the searched butt joint ring line segment brightness.
8. The image-based non-cooperative target docking ring extraction method according to claim 1, wherein: judging whether the brightness of the pixel points on the left auxiliary line and the right auxiliary line in the set area is less than T or not2The judging method comprises the following steps: when the radiation line continues to travel until the brightness is less than the threshold T2When the pixel (2) is recorded, the distance S2 from the starting point (x0, y0) to the position (i.e., the pixel) of the radiation line is recorded, and whether the brightness of the left and right auxiliary lines is less than the threshold T in the region from the starting point S2-r to the starting point S2+ r is determined2The pixel of (2).
9. The image-based non-cooperative target docking ring extraction method according to claim 1, wherein: in the method for determining the inner edge and the outer edge of the butting ring in the sixth step, the inner edge points are as follows: the three parallel lines in the fourth step all have the brightness larger than the threshold value T in a certain area2Along the radiation direction, the brightness of three lines is greater than T2The first pixel of (2) is the inner edge point of the docking ring respectively; its outer edge points are: after the radiation line continues to advance by N pixels in the step five, if the brightness of all three parallel lines in a certain area is less than the threshold value T2Along the radiation direction, the brightness of three lines is less than T2The first pixels of (a) are the outer edge points of the docking ring respectively.
10. The image-based non-cooperative target docking ring extraction method according to claim 1, wherein: t is1And extracting the brightness threshold of the non-cooperative target satellite from the image.
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