CN111127542B - 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 docking collar 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 butting ring line segment, namely the width of the butting ring line segment; the brightness indicates the magnitude of the gray value of the segment of the docking collar segment. After the three attributes are set to a certain range of constraint values, only the docking ring segment has the attribute, and the background area does not have the attribute, so that the docking ring segment can be found by searching the segment meeting the three attributes. And finally fitting the docking ring according to the found line segments. The method realizes high-precision identification of the docking ring under the condition of space complex illumination, so as to facilitate subsequent works such as docking fuel filling.
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
In the process of approaching the non-cooperative target satellite, the space camera shoots a docking ring image of the non-cooperative target satellite, and then the docking ring is identified from the image. And the relative position and the relative posture of the target star can be measured according to the identified docking ring.
There have been some research achievements in recent years:
some methods are completed through deep learning, the storage space required by the program is large, the storage space of the existing hardware platform is limited, the storage cannot be completed, the internal principle of the program is not completely transparent, and the failure probability exists, so that the method is unacceptable in space application.
Some methods calculate the docking collar circle from the formed trajectory by continuously capturing the target. The required acquisition time is long, and real-time requirements are difficult to meet.
Some methods detect edges by operators, then extract and classify the edges, and finally detect circles. The method has the advantages of complex flow, high calculation amount and difficulty in extracting the target circle in the existing hardware platform and the specified time.
Some carry out the circle extraction of docking ring through improving the circle transformation algorithm, but this kind of method complexity is high, and the hardware platform is difficult to operate in space low operational capability, and under the complex illumination condition in space, the accuracy is low.
By using the circle detection method, the image recognition of the docking ring in the space environment is difficult to finish. Firstly, polyimide on the surface of a star reflects sunlight, and different highlight areas are formed on the surface, so that a complex background with uneven brightness is formed; secondly, the docking ring is not completely highlighted, some areas are darker, some areas are bright, but the brightness is uneven, as shown in fig. 2, and these factors cause that the identification of the space non-cooperative target docking ring is difficult to finish by the traditional method; finally, in the convergence, 10 images per second are required to be processed, 10 pose information is calculated, and under the low-computing-capability platform, the algorithm complexity is required to be very low, as shown in fig. 2.
Disclosure of Invention
The invention aims to solve the technical problems that: the method for extracting the non-cooperative target docking ring based on the image comprises the steps of dividing the docking ring into different line segments, searching the docking ring segments from different directions according to the three attributes of each docking ring segment, namely length, width and brightness, and fitting the whole docking ring after the docking ring segments are found, wherein the method is high in test calculation speed, robustness and precision.
The invention aims at realizing the following technical scheme: the non-cooperative target docking ring extraction method based on the image sequentially comprises the following steps:
step one, a space camera shoots an image of a non-cooperative target satellite, an O-XY two-dimensional orthogonal coordinate system is established, a horizontal right direction is defined as an x-axis positive direction, a vertical upward direction is defined as a y-axis positive direction, the x-axis and the y-axis are positioned in a plane where the whole image is positioned, and a lower left corner of the image is a coordinate origin (0, 0). Calculating that the brightness in the image is greater than the brightness threshold T 1 Based on the x-coordinate and y-coordinate values of such pixels, the mean (x 0, y 0) of the x-coordinate and y-coordinate values of such pixels is determined.
Step two, setting an outward radiation direction by taking (x 0, y 0) as a starting point, wherein the radiation interval between two adjacent radiation directions is D degrees;
step three, each outward radiation direction is provided with two parallel lines which are symmetrically arranged at two sides of each radial line except the radiation line passing through the starting point (x 0, y 0) and used for assisting in finding the butt joint ring, each radial line and the two corresponding auxiliary lines form three parallel lines, the butt joint ring is found by extending the three parallel lines along the radiation direction, 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. (the docking ring is a circle composed of a plurality of segments)
Step four, in an outward radiation direction, when a pixel is found along the radiation line, judging whether the brightness of the pixel is greater than a brightness threshold T 2 Simultaneously judging 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 also greater than a brightness threshold T 2 If yes, judging that the inner edge of the butt joint ring is suspected to be found, turning to the fifth step, otherwise, continuing to find the three parallel lines, namely the radial line and the auxiliary line, along the radial direction until the set length range is found, and stopping finding. (T herein) 2 And the brightness attribute of the corresponding butt joint ring line segment. )
Step five, continuing searching along the radiation direction, wherein the brightness is greater than the brightness threshold T in the step four 2 After advancing N pixels at the pixel position, judging whether the brightness is less than T 2 Simultaneously judging whether the brightness of the pixels in the set area on the left auxiliary line and the right auxiliary line is less than T 2 If the conditions are met at the same time, judging that the outer edge of the docking ring is suspected to be found, and ending the docking ring search; otherwise, the three parallel lines, namely the radial line and the auxiliary line, continue to search along the radial direction until the set length range is searched, and stop searching. (where N corresponds to the docking collar 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 butt joint ring according to the inner edge points and the outer edge points of the butt joint ring searched in each radiation direction.
Preferably, in the second step, the calculating method of the radiation interval D degree between two adjacent radiation directions includes: the value of D can be adjusted between 10 degrees and 45 degrees, D is an adjustable parameter, and if D is 45 degrees, the D indicates that 8 radiation directions exist, namely 8 butt joint ring line segments are found in the 8 radiation directions.
Preferably, starting points of the three parallel lines in the third step are respectively: the middle line, the origin of the line of radiation, is (x 0, y 0); the other two lines, namely, the two auxiliary lines, start at points (x 0, y 0) respectively shifted by M/2 pixels to both sides along the direction perpendicular to the radial line.
Preferably, in the fourth step, it is determined whether the brightness of the pixels in the set region on the left and right auxiliary lines of the radiation in the radiation direction is also greater than the brightness threshold T 2 The judging method of (1) is as follows: when the radiation travels to a brightness greater than the threshold T 2 For the pixels of (a), the distance S1 of the radiation line from the starting point (x 0, y 0) to the point (i.e. the pixel) is recorded, and whether the brightness of the left and right auxiliary lines is greater than the threshold T is judged in the region from the respective starting points S1-r to S1+ r 2 Is a pixel of (c).
Preferably, in the fifth step, it is determined whether the brightness of the pixel points on the left and right auxiliary lines in the set area is less than T 2 The judging method of (1) is as follows: when the radiation continues to travel to brightnessLess than threshold T 2 For each pixel of (2), the distance S2 of the radiation line from the starting point (x 0, y 0) to the point (i.e. the pixel) is recorded, and it is determined whether the brightness of the left and right auxiliary lines is less than the threshold T in the region from the respective starting point S2-r to S2+ r 2 Is a pixel of (c).
Preferably, in the step six, the method for determining the inner edge and the outer edge of the butt joint ring includes: the brightness of the three parallel lines in the fourth step is larger than the threshold value T in a certain area 2 Along the radiation direction, the brightness of the three lines is greater than T 2 The first pixel of (a) is the inner edge point of the butt joint ring respectively; the outer edge points are as follows: after the radiation line continues to advance N pixels in the fifth step, if all three parallel lines have brightness less than the threshold value T in a certain area 2 Along the radiation direction, the brightness of the three lines is less than T 2 The first pixel of (a) is the outer edge point of the docking ring, respectively.
Preferably, the non-cooperative target is a satellite, and the requirement of shooting the image of the non-cooperative target is that when the space camera carried by the satellite approaches to the docking ring direction of the non-cooperative target satellite within 100 meters, the space camera shoots the docking ring of the non-cooperative target satellite, at this time, the satellite completes the recognition work of the docking ring according to the docking ring image shot by the space camera, and according to the recognized docking ring, the relative position and posture of the non-cooperative target satellite can be calculated, and then the satellite approaches to the non-cooperative target satellite, and the non-cooperative target satellite is captured or space fuel is filled.
Preferably, M is the length of the found docking ring segment, corresponding to the docking ring segment length attribute.
Preferably, N is the width of the found docking ring segment, corresponding to the docking ring segment width attribute.
Preferably T 2 And the brightness of the searched butt-joint ring line segment corresponds to the brightness attribute of the butt-joint ring line segment.
Preferably T 1 A luminance threshold of the non-cooperative target satellite is extracted for 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. The recognition of the docking ring is simplified into the recognition of different docking ring segments, so that the complex problem is simplified, and a method for rapidly solving the problem is found.
(2) The invention provides three unique attributes of the docking ring segment. The different line segments are classified into three attributes of length, width and brightness, only the butt joint ring has the attribute, and the background does not simultaneously meet the area of certain length, width and brightness, so that the searched target characteristic is further simplified and unique. In a complex bright and dark background, three attributes are met, namely, the section of the docking ring is high in precision and Lu Bangjiang, and the docking ring can be found under the high complex background after testing.
(3) In the process of searching the butting ring line segments, the three parallel lines are used for searching, so that the calculation process is further simplified, and the operation efficiency is high.
(4) In the invention, the circle center of the docking ring can be fitted by only identifying 3 line segments. The robustness is high.
(5) The invention has the advantages of no complicated comparison and screening, high speed and suitability for space embedded platform operation.
(6) The invention has wide applicability, and M T in the third, fourth and fifth steps is adjusted by the adjustment algorithm 2 N parameter value, namely adjust and look for length, luminance, width parameter of one section of the butt joint ring, can find the butt joint ring which meets different width, luminance characteristic. Only parameters need to be adjusted to meet the requirements of different docking rings.
Drawings
FIG. 1 is a flow chart of the steps of the present invention;
FIG. 2 is a schematic diagram of a spatially non-cooperative target docking ring;
FIG. 3 is a segmented schematic view of a docking collar;
FIG. 4 is a schematic view 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 view of the invention looking for a docking ring in other directions.
Detailed Description
The invention will now be described in detail with reference to the drawings and specific examples.
The invention provides an image-based non-cooperative target docking ring extraction method. Each docking collar 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 butting ring line segment, namely the width of the butting ring line segment; the brightness indicates the magnitude of the gray value of the segment of the docking collar segment. After the three attributes are set to a certain range of constraint values, only the docking ring segment has the attribute, and the background area does not have the attribute, so that the docking ring segment can be found by searching the segment meeting the three attributes. And finally fitting the docking ring according to the found line segments. The method realizes high-precision identification of the docking ring under the condition of space complex illumination, so as to facilitate subsequent works such as docking fuel filling.
When searching for the identification method, the extraction of the docking ring in fig. 2 is found, and the extraction of different docking ring segments in the docking ring can be changed. As shown in fig. 3, the docking ring is decomposed into white docking ring segments at different positions, and the length and number of the white docking ring segments can be set by itself, and in the following figure, 8 segments are taken as an example. Further, if desired, expansion can be made to 16, 32 segments, etc. at different locations.
Each docking collar segment has three attributes, length, width, and brightness. The length represents the length range of the segment of the docking ring, i.e., the length of the segment of the docking ring; the width represents the width range of the segment of the docking ring, i.e., the width of the segment of the docking ring; brightness represents the magnitude of the gray value of the docking collar segment. These three attributes can represent a segment of the docking ring, and after the three attributes are set to a range of constraint values, only the docking ring segment has the attribute, and the background area does not have the attribute, so that the docking ring segment can be found by searching for the segment satisfying the three attributes.
In the implementation process of the invention, the purpose of rapidly identifying the docking ring can be achieved on the embedded platform, and the method is found out through tests, and has the advantages of high precision, high speed, strong robustness and wide practicability.
After several years of operation of the spatially non-cooperative target satellite, the spatially non-cooperative target satellite needs to be captured and refueled for extended operation time due to fuel exhaustion. In the satellite capturing process, one characteristic of the 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. Simply identifying the filler neck, because the target is too small, is very difficult to identify, especially at long distances, and is difficult to directly accomplish identification. Therefore, the filling port is further found by identifying the docking ring. The identification of the docking ring becomes very critical.
The space is free from atmosphere, and after sunlight irradiates the docking ring directly, the docking ring and the star are led to be uneven in brightness through multiple scattering, so that a high-brightness and high-darkness area exists. Through testing the existing docking ring or circle extraction algorithm, the method is difficult to be applied in a space environment. The space computer has lower calculation efficiency, the storage space allocated to the docking ring identification program is small, but the task itself needs 10Hz calculation capability, namely, the processing of 10 images is completed every second, and the conventional docking ring or circle extraction algorithm is difficult to meet the task requirement in terms of the running speed and the storage space.
Aiming at imaging of a space target, the invention provides a docking ring extraction method which has low complexity and high precision, and meets the task requirement through practical verification.
As shown in fig. 1, the method for extracting the non-cooperative target docking ring based on the image of the present invention preferably comprises the following steps:
firstly, shooting an image of a non-cooperative target, establishing an O-XY two-dimensional orthogonal coordinate system, defining that the horizontal direction is the positive direction of an x axis, the vertical direction is the positive direction of a y axis, the x axis and the y axis are positioned in the plane of the whole image, the lower left corner of the image is the origin (0, 0), and calculating that the brightness in the image is larger than a brightness threshold T 1 To find the mean (x 0, y 0) of such pixels in x-and y-coordinates, specifically:
the space camera is installed in front of the satellite, and is in the process of approaching the non-cooperative target satelliteDocking a ring to a 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 defined as the positive direction of the x axis, the vertical upward direction is defined as the positive direction of the y axis, the x axis and the y axis are positioned in the plane of the whole image, and the lower left corner of the image is the origin (0, 0) of coordinates. Calculating that the brightness in the image is greater than the brightness threshold T 1 Is statistically greater than the luminance threshold T 1 The x-coordinate and y-coordinate values of the pixels of the (c) are averaged (x 0, y 0) in the x-coordinate and y-coordinate values of the pixels.
In the calculated image the luminance is greater than the luminance threshold T 1 In the pixel process of (2), the gray average value v of all pixels in the image is obtained mean Maximum gray value v in image max Minimum gray value v in image min . Wherein v is max The optimal selection value meets two conditions, namely, 10 or more pixels are larger than the pixel value, and the maximum value is selected from the pixels meeting the first condition; v min The value also needs to satisfy two conditions, namely, 10 or more pixels are smaller than or equal to the pixel value, and the minimum value is selected from the pixels satisfying the first condition. Such taking maximum and minimum values prevents noise points from interfering with the computation.
T of luminance threshold 1 The calculation method is preferably
Not only the maximum gray value v max Subtracting the minimum gray value v min After taking half the difference value of (a), the gray average value v of all pixels mean The absolute value of the difference is then averaged over the gray scale v of all pixels mean The absolute value is subtracted.
Step two, setting an outward radiation direction with (x 0, y 0) as a center, wherein the radiation interval between two adjacent radiation directions is D degrees, and the preferable radiation interval is:
and the first image is subjected to initial capture mode image processing. The second image starts and tracking mode image processing is performed.
In the initial capture mode image processing, the preferred method of determining the radiation interval D is:
the radiation interval D between two adjacent radiation directions is initially set to be preferably 120 degrees, and then three radiation directions are total. Preferably, it is: the first radial line direction takes (x 0, y 0) as a starting point, and forms an angle of 0 degrees with the x axis along the horizontal right direction; the second radial line direction takes (x 0, y 0) as a starting point, and the anticlockwise radial line and the first radial line form an angle direction of 120 degrees; the second radial line direction is from (x 0, y 0), and is in an angle of 240 degrees with respect to the first radial line in the counterclockwise direction. The butt-joint ring segments are found in these three radiation directions.
The further preferable scheme is as follows: if only one radiation direction finds the butting ring line segment, the radial line direction is taken as the initial direction, the radial direction is changed by taking D/4 degree as the step length in the anticlockwise direction, the radial direction is searched in each radiation direction until H butting ring line segments are found, and the search is ended. If H butt joint ring segments are not found after finding one circle, the step length is reduced by half, namely D/8 degree, and finding is carried out in each radiation direction; if not found, the moving interval is reduced by half, namely D/16 degree, until H butt joint ring segments are found.
The further preferable scheme is as follows: if only two radiation directions find the butting ring line segments, the included angle center line of the two radiation directions is taken as the initial direction, the two radiation directions are moved in the anticlockwise direction by taking D/4 degree as the step length, the radiation directions are changed, and the butting ring line segments are searched in each radiation direction until H butting ring line segments are found, and the search is finished. If the abutting ring segment is not found after finding a circle, the step length is reduced by half, namely D/8 degree, and finding is carried out in each radiation direction; if not found, the moving interval is reduced by half, namely D/16 degree, until H butt joint ring segments are found.
The further preferable scheme is as follows: if the three radiation directions all find the butting ring line segments, or if the three radiation directions all do not find the butting ring line segments, the first radiation direction is taken as the initial direction, the first radiation direction is moved anticlockwise by taking D/4 degree as the step length, the radiation directions are changed, the search is performed in each radiation direction until the H butting ring line segments are found, and the search is finished. If H butt joint ring segments are not found after finding one circle, the step length is reduced by half, namely D/8 degree, and finding is carried out in each radiation direction; if not found, the moving interval is reduced by half, namely D/16 degree, until H butt joint ring segments are found.
In tracking mode image processing, the preferred method of determining the radiation interval D is:
and searching the butting ring line segment in the image according to the radiation direction of the found butting ring line segment in the previous image. The preferable scheme is as follows: and if the found docking ring segments are equal to H, ending the search. If the found butting ring line segments are smaller than H, the radial line direction of the first found butting ring line segment in the image is taken as the initial direction, the radial direction is changed by taking D/4 degree as the step length along anticlockwise direction, the search is carried out in each radial direction until the H butting ring line segments are found, and the search is ended. The further preferable scheme is as follows: if H butt joint ring segments are not found after finding one circle, the step length is reduced by half, namely D/8 degree, and finding is carried out in each radiation direction; if not found, the moving interval is reduced by half, namely D/16 degree, until H butt joint ring segments are found.
H is a set parameter, preferably greater than 3.
Taking each radial line as a center except the radial line passing through the center (x 0, y 0), symmetrically arranging two parallel lines serving as auxiliary lines respectively for assisting in finding a butt joint ring, wherein each radial line and the two corresponding auxiliary lines form three parallel lines, the butt joint ring is found by extending the three parallel lines along the radial direction, the distance between the two symmetrically arranged auxiliary lines is M pixels, and the distance from each auxiliary line to the radial line is M/2; m is the length of the butt joint ring line segment to be found, and specifically is:
and the first image is subjected to initial capture mode image processing. The second image starts and tracking mode image processing is performed.
In the initial capture mode image processing, M is a given value.
In tracking mode image processing, M is automatically adjusted. The M automatic adjustment process is preferably as follows:
if a certain radiation direction finds a butt-joint ring segment, then that radiation directionThe radial line and the two auxiliary lines form a line segment respectively from the inner edge to the outer edge of the butt joint ring along the searching direction, and the line segment is respectively marked as a radial line segment, an auxiliary line segment 1 and an auxiliary line segment 2. The gray average value of each of the three line segments is respectively recorded as v 0 、v 1 、v 2 . The current image preferably has the radiation direction M value of
Where k is a coefficient, M p The distance between the two auxiliary lines of the radiation direction for the upper image; v 0 、v 1 、v 2 In the above image, in the radiation direction, 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.
If the radiation direction does not find a docking collar segment or does not query for a docking collar segment in the previous image, M is preferably the most recently calculated value.
Step four, in an outward radiation direction, when a pixel is found along the radiation line, finding that the brightness of the pixel is greater than the set background brightness threshold T 2 Judging whether the brightness of 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 T 2 If yes, judging that the inner edge of the butt joint ring is suspected to be found, turning to the fifth step, otherwise, continuing to find three parallel lines, namely the radial line and the auxiliary line, along the radial direction until a set length range L is found 1 The search is stopped.
And the first image is subjected to initial capture mode image processing. The second image starts and tracking mode image processing is performed.
In the initial capture mode image processing, the luminance threshold T 2 The preferred calculation method of (a) is
T 2 ＝T 1 +t
Wherein T is 1 Preferably the central threshold is calculated in step one, t being a given parameter.
In tracking mode image processing, the luminance threshold T 2 The preferred calculation method of (a) is
V in the above 0 、v 1 、v 2 The calculation method is the same as the third step; if the radiation direction does not find the docking ring in the previous image, T 2 The most recently calculated values are used.
Length L in initial capture mode image processing 1 Is given by the value.
Length L in tracking mode image processing 1 The calculation method of (a) is preferably
L 1 ＝max{l 1 ,l 2 ,...,l i }+l d
Wherein l 1 ,l 2 ,...,l i In the above image, the length value from the radial line starting point to the outer edge point of the butt joint ring is found in the butt joint ring segment; l (L) d Is a given parameter.
The starting point of the line of radiation is (x 0, y 0). The calculation method of the starting points of the two auxiliary lines is that the falling points after M/2 movement are respectively started from (x 0, y 0) along the two directions perpendicular to the radial lines, namely the respective starting points of the two radial lines. The radial line and the two auxiliary lines search for the butt-joint ring line segment from the respective starting points along the direction parallel to the radial line.
Step five, continuing searching along the radiation direction, wherein the brightness is greater than the brightness threshold T in the step four 2 After advancing N pixels at the pixel position, judging whether the brightness is less than T 2 Simultaneously judging whether the brightness of the pixels in the set area on the left auxiliary line and the right auxiliary line is less than T 2 If the conditions are met at the same time, judging that the outer edge of the docking ring is suspected to be found, and ending the docking ring search; otherwise, the three parallel lines, namely the radial line and the auxiliary line, continue to search along the radial direction until the set length range is searched, and stop searching. Where N corresponds to the docking collar segment width attribute.
In the initial capture mode image processing, the advancing pixel N is a given value.
In the tracking mode image processing, the calculation method of the advancing pixel N is preferably,
N＝min{n 1 ,n 2 ,...,n i }-n d
wherein n is 1 ,n 2 ,...,n i In the upper image, along the radial line, the distance between the inner edge point and the outer edge point of the butt joint ring is searched, n d Is a given parameter.
And step six, after the abutting ring segments in one direction are searched, the abutting ring segments in the next direction are searched until all directions are searched, and the abutting rings are fitted according to the inner edge points and the outer edge points of the abutting ring segments searched in the outward radiation directions.
The invention further realizes the improvement of extraction precision:
in the third step, in the tracking mode, M is automatically adjusted according to the calculation condition of the previous image. In tracking mode, the current radiation direction M value is preferably:
wherein l i The radiation line is a distance from the start point to the inner edge of the butt joint ring for the upper image; f (f) i 1 、f i 2 For the upper image, the distance between the two auxiliary lines in the radiation direction from the respective starting points to the inner edge of the butt joint ring; i f i 1 -l i The I is the absolute value of the difference between the distance from the starting point to the inner edge of the butt joint ring of an auxiliary line in the radiation direction of the previous image and the distance from the starting point to the inner edge of the butt joint ring of the radiation line; i f i 2 -l i The I is the absolute value of the difference between the distance from the starting point to the inner edge of the butt joint ring and the distance from the radial line to the inner edge of the butt joint ring of the other auxiliary line of the radiation direction of the previous image; m is M p The distance between the two auxiliary lines of the radiation direction for the upper image; v 0 、v 1 、v 2 In the above image, in the radiation directionThe gray average values of the radiation line segment, the auxiliary line segment 1 and the auxiliary line segment 2 formed by the radiation line and the two auxiliary lines from the inner edge to the outer edge of the butt joint ring; i. j and k are coefficients.
The further preferable scheme for realizing the improvement of the extraction speed is as follows:
in the second step, the tracking mode image processing method for starting the second image comprises the following steps:
the radiation line and two auxiliary lines of each found butt joint ring line segment in the previous image 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 value of each of the three line segments is respectively recorded as v 0 、v 1 、v 2 . Calculation of v 0 、v 1 、v 2 Gray mean value and background gray threshold T 1 Preferably, the difference value calculation formula is as follows
Then, the sum of the difference between the distance from the starting point to the inner edge of the butt joint ring of the two auxiliary lines of the radiation direction and the distance from the starting point to the inner edge of the butt joint ring of the radial line in the upper image is calculated, and the calculation formula is preferably as follows
|f i 1 -l i |+|f i 2 -l i |
The above two factors are weighted to determine the degree of merit of the radiation direction in the previous image, and the calculation formula of the degree of merit is preferably as follows
In the previous image, all the searched docking ring segments are sequenced according to the above formula, and the three radiation directions which are sequenced at the front are taken as the three radiation directions of the current image for searching the docking ring. If the three directions of the current image find the butting ring line segments, the finding is finished. If the three directions of the current image cannot find three butting ring segments, the traditional method is restored, the radial line direction of the first butting ring segment found in the current image is taken as the initial direction, the radial direction is changed by taking D/4 degree as the step length along the anticlockwise direction, the search is carried out in each radial direction until H butting ring segments are found, and the search is ended. If H butt joint ring segments are not found after finding one circle, the step length is reduced by half, namely D/8 degree, and finding is carried out in each radiation direction; if not found, the moving interval is reduced by half, namely D/16 degree, until H butt joint ring segments are found.
The further preferable scheme for realizing the improvement of the extraction stability is as follows:
in the fourth step, in the tracking mode, the radiation line and the left and right auxiliary lines have respective brightness threshold values, and the brightness threshold value of the radiation lineAnd the brightness threshold value of the left auxiliary line and the right auxiliary line>The preferred calculation method of (a) is
In the non-cooperative target docking ring extraction method based on the image, the further preferable scheme is as follows:
the first image is subjected to initial capture mode calculation, and the preferable scheme is as follows:
in the step (1), in the whole image, the horizontal right direction is the positive direction of the x coordinate, the vertical upward direction is the positive direction of the y coordinate, and the lower left corner of the image is the origin (0, 0) of coordinates. Pixels with brightness greater than a certain threshold are calculated, and the average value (x 0, y 0) of the pixel values in xy coordinates is obtained.
And (2) taking (x 0, y 0) as a center, and radiating outwards to find the docking ring. Each radiation is spaced D degrees apart. And D is adjustable in parameter, and the D is preferably 45 degrees, so that 8 radiations exist, namely 8 butt joint ring line segments are found in 8 directions. The 8 radiation directions are shown in fig. 4.
And (3) adopting three parallel lines in each radiation direction, and extending and searching the parallel lines to obtain a middle radial line and left and right auxiliary lines respectively. The left auxiliary line and the right auxiliary line, namely the outermost two parallel lines, are separated 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 origin of the radiation is (x 0, y 0); the other two auxiliary line starting points are points respectively 8 pixels shifted to two sides along the radiation direction perpendicular to the middle line. As shown in fig. 5, to show a starting point when looking for a direction in the docking ring, a white point is a middle line starting point, and two white circles are two auxiliary line starting points. Here the value of M is preferably 16.
In step (4), preferably, when the line of radiation travels to a pixel having a luminance greater than the luminance threshold 120, the distance 260 from the start point to the point of the line of radiation is recorded, and it is determined whether or not there are points having a luminance greater than the luminance threshold 120 in the region of the left and right auxiliary lines from the start point 240 to 280. If yes, the inner edge of the butt joint ring is considered to be suspected 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 segment brightness attribute, i.e. the brightness attribute of the docking collar.
And (5) continuing to advance the middle radiation line by 50 pixels, recording the distance 300 from the starting point to the middle radiation line when the middle radiation line continues to advance to the pixel with the brightness smaller than the threshold value 120, and judging whether the left auxiliary line and the right auxiliary line have the brightness smaller than the average value 120 of the background brightness in the area from 280 to 320 of the starting point. If so, the joint is considered as a butt joint ring.
And (6) searching for the docking ring in the next direction after searching for the docking ring in one direction, until all the set directions are searched for. A schematic diagram of looking for other directional docking loops is shown in fig. 6.
Starting a second image, and performing tracking mode calculation, wherein the calculation process is as follows:
in the step (1), in the whole image, the horizontal right direction is the positive direction of the x coordinate, the vertical upward direction is the positive direction of the y coordinate, and the lower left corner of the image is the origin (0, 0) of coordinates. Pixels with brightness greater than a certain threshold are calculated, and the average value (x 0, y 0) of the pixel values in xy coordinates is obtained.
And (2) taking (x 0, y 0) as a center, and radiating outwards to find the docking ring. And each radiation direction in the previous image, the radial line on the butt joint ring and the difference value between the gray average value of the two auxiliary lines and the background gray threshold value, all radial line directions are ordered according to the difference value, and the first three radiation directions with the largest difference value are taken as the three directions for the initial searching 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 the three directions are respectively searched along the three radiation directions.
And (3) extending and searching three parallel lines in each radiation direction, wherein the three parallel lines are respectively a middle line and two auxiliary lines. The M values for the three directions of radiation are calculated as 15, 16, 14, respectively, i.e. the outermost two parallel lines of the three directions of radiation are spaced 15, 16, 14, respectively. The starting points of the three parallel lines are respectively: the origin of the radiation is (x 0, y 0); the other two auxiliary lines start from points (x 0, y 0) respectively moving by M/2 along the direction perpendicular to the radial line.
And (4) taking one of the radiation directions, and calculating the brightness threshold value to be 125. When the intermediate line of radiation travels to a pixel having a luminance greater than 125, the distance 265 from the start point to the point is recorded and it is determined whether there are points of greater luminance than the luminance threshold 125 in the region of the left and right auxiliary lines from the start point 245 to 285. If yes, the inner edge of the butt joint ring is considered to be suspected 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 segment brightness attribute, i.e. the brightness attribute of the docking collar.
And (5) continuing to advance the middle radial line by 50 pixels, recording the distance 306 from the starting point to the middle radial line when the middle radial line continues to advance to the pixel with the brightness less than the brightness threshold 125, and judging whether the left auxiliary line and the right auxiliary line have points with the brightness less than the background brightness threshold 125 in the region from the starting point 286 to 326. If so, the joint is considered as a butt joint ring.
And (6) searching for the docking ring in the next radiation direction after searching for the docking ring in one radiation direction, until the three radiation directions are searched for.
Through the test in the scheme, the method provided by the invention has high accuracy of extracting the docking ring, and the error is found to be within 5mm by testing the extraction accuracy of the docking ring for 10 times, and the method is specifically shown in the following table 1. This accuracy is achieved to meet the meeting docking requirements.
TABLE 1 Butt-joint ring extraction error table
The 10 docking ring extraction speed tests found that all calculations were completed within 60ms, see in particular table 2 below. This speed is accomplished to meet meeting the mating 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. The recognition of the docking ring is simplified into the recognition of different docking ring segments, so that the complex problem is simplified, and a method for rapidly solving the problem is found. The invention provides three unique attributes of the docking ring segment. The different line segments are classified into three attributes of length, width and brightness, only the butt joint ring has the attribute, and the background does not simultaneously meet the area of certain length, width and brightness, so that the searched target characteristic is further simplified and unique. In a complex bright and dark background, three attributes are met, namely, the section of the docking ring is high in precision and Lu Bangjiang, and the docking ring can be found under the high complex background after testing.
In the process of searching the segments of the docking ring, the invention further simplifies the calculation process by searching three parallel lines, has high operation efficiency, and can fit the circle center of the docking ring only by identifying 3 segments. The method has high robustness, does not have complicated comparison and screening, has high speed and is suitable for space embedded platform operation.
The invention has wide applicability, and M T in the third, fourth and fifth steps is adjusted by the adjustment algorithm 2 N parameter value, namely adjust and look for length, luminance, width parameter of one section of the butt joint ring, can find the butt joint ring which meets different width, luminance characteristic. Only parameters need to be adjusted to meet the requirements of different docking rings.
What is not described in detail in the present specification is a well known technology to those skilled in the art.
Claims (10)
1. An image-based non-cooperative target docking ring extraction method is characterized by comprising the following steps of: the method comprises the following steps:
firstly, shooting an image of a non-cooperative target satellite by a space camera, establishing an O-XY two-dimensional orthogonal coordinate system, defining a horizontal right direction as an x-axis positive direction, a vertical upward direction as a y-axis positive direction, wherein 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 an origin (0, 0) of coordinates; calculating that the brightness in the image is greater than the brightness threshold T 1 According to the x coordinate value and the y coordinate value of the pixel, calculating the average value (x 0, y 0) of the x coordinate and the y coordinate of the pixel;
step two, setting an outward radiation direction by taking (x 0, y 0) as a starting point, wherein the radiation interval between two adjacent radiation directions is D degrees;
step three, each outward radiation direction is provided with two parallel lines which are symmetrically arranged at two sides of each radial line except the radiation line passing through the starting point (x 0, y 0) and used for assisting in finding the butt joint ring, each radial line and the two corresponding auxiliary lines form three parallel lines, the butt joint ring is found by extending the three parallel lines along the radiation direction, 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 pixel is found along the radiation line, judging whether the brightness of the pixel is greater than a brightness threshold T 2 Simultaneously judging 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 also greater than a brightness threshold T 2 If yes, judging that the inner edge of the butt joint ring is suspected to be found, turning to the fifth step, otherwise, continuing to find three parallel lines, namely the radial line and the auxiliary line, along the radial direction until a set length range is found, and stopping finding;
step five, continuing searching along the radiation direction, wherein the brightness is greater than the brightness threshold T in the step four 2 After advancing N pixels at the pixel position, judging whether the brightness is less than T 2 Simultaneously judging whether the brightness of the pixels in the set area on the left auxiliary line and the right auxiliary line is less than T 2 If the conditions are met at the same time, judging that the outer edge of the docking ring is suspected to be found, and ending the docking ring search; otherwise, the three parallel lines, namely the radial line and the auxiliary line, continue to search along the radial direction until the set length range is searched, and stop 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 butt joint ring according to the inner edge points and the outer edge points of the butt joint ring searched in each radiation direction.
2. The method for extracting the non-cooperative target docking ring based on the image according to claim 1, wherein the method comprises the following steps: the method for calculating 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, and if D is 45 degrees, the D indicates that 8 radiation directions exist, namely 8 butt joint ring line segments are found in the 8 radiation directions.
3. The method for extracting the non-cooperative target docking ring based on the image according to claim 1, wherein the method comprises the following steps: m is the length of the found butt-joint ring line segment, and corresponds to the length attribute of the butt-joint ring line segment.
4. The method for extracting the non-cooperative target docking ring based on the image according to claim 1, wherein the method comprises the following steps: the starting points of the three parallel lines in the third step are respectively as follows: the middle line, the origin of the line of radiation, is (x 0, y 0); the other two lines, namely, the two auxiliary lines, start at points (x 0, y 0) respectively shifted by M/2 pixels to both sides along the direction perpendicular to the radial line.
5. The method for extracting the non-cooperative target docking ring based on the image according to claim 1, wherein the method comprises the following steps: n is the width of the found butt-joint ring line segment and corresponds to the width attribute of the butt-joint ring line segment.
6. The method for extracting the non-cooperative target docking ring based on the image according to claim 1, wherein the method comprises the following steps: in the fourth step, it is determined whether the brightness of the pixels in the set region on the left and right auxiliary lines of the radiation line in the radiation direction is also greater than the brightness threshold T 2 The judging method of (1) is as follows: when the radiation travels to a brightness greater than the threshold T 2 Recording the distance S1 from the starting point (x 0, y 0) to the pixel, judging whether the brightness of the left and right auxiliary lines is greater than the threshold value T in the region from the starting point S1-r to S1+ r 2 Is a pixel of (c).
7. The method for extracting the non-cooperative target docking ring based on the image according to claim 1, wherein the method comprises the following steps: t (T) 2 And the brightness of the searched butt-joint ring line segment corresponds to the brightness attribute of the butt-joint ring line segment.
8. The method for extracting the non-cooperative target docking ring based on the image according to claim 1, wherein the method comprises the following steps: in the fifth step, it is determined whether the brightness of the pixel points on the left and right auxiliary lines in the set region is less than T 2 The judging method of (1) is as follows: when the radiation continues to travel to a brightness less than the threshold T 2 For each pixel of (2), the distance S2 from the start point (x 0, y 0) to the pixel is recorded, and the left and right auxiliary lines are determined to be from the respective start points S2-r toWithin the S2+r region, whether the brightness is less than the threshold T 2 Is a pixel of (c).
9. The method for extracting the non-cooperative target docking ring based on the image according to claim 1, wherein the method comprises the following steps: in the sixth step, the method for determining the inner edge and the outer edge of the butt joint ring comprises the following steps: the brightness of the three parallel lines in the fourth step is larger than the threshold value T in a certain area 2 Along the radiation direction, the brightness of the three lines is greater than T 2 The first pixel of (a) is the inner edge point of the butt joint ring respectively; the outer edge points are as follows: after the radiation line continues to advance N pixels in the fifth step, if all three parallel lines have brightness less than the threshold value T in a certain area 2 Along the radiation direction, the brightness of the three lines is less than T 2 The first pixel of (a) is the outer edge point of the docking ring, respectively.
10. The method for extracting the non-cooperative target docking ring based on the image according to claim 1, wherein the method comprises the following steps: t (T) 1 A luminance threshold of the non-cooperative target satellite is extracted for the image.
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