Method for measuring parachute swing angle in rocket sled-throwing drag parachute test

Abstract

The invention discloses a method for measuring a parachute swing angle in a rocket sled-throwing drag parachute test, and relates to the field of angle metering. According to the method, a camera is installed on a rocket sled pulley to carry out the drag parachute throwing test, the camera is used for shooting a motion track image of the tail end of a main parachute rope node of a drag parachute, and then the camera is calibrated to calculate internal and external orientation elements of the camera; calculating image space coordinates of a node at the tail end of a main parachute cord of the drag parachute by using a collinear condition equation, a rotation matrix and space coordinate translation; according to the fact that a space straight line passing through the projection center of the camera and the image point of the main parachute cord also passes through the tail end node of the main parachute cord of the drag parachute, the intersection point of the space straight line and the motion trail of the main parachute cord of the drag parachute is solved, the space coordinates of the tail end node of the main parachute cord are obtained, and then the pitching swing angle and the horizontal swing angle of the drag parachute are calculated. Compared with an existing binocular camera measuring method, the method for measuring the parachute swing angle in the rocket sled-throwing drag parachute test has the advantages that the number of cameras is reduced, the workload of swing angle calculation is reduced, and the measuring efficiency is improved.

Description

Technical Field

[0001] The present application relates to the field of angle measurement, and in particular to a method for measuring the parachute swing angle in a rocket sled-throwing drag parachute test. Background Art

[0002] A drag parachute is a type of parachute used to assist high-speed aircraft landings. As a flexible decelerator featuring light weight, compact size, and a large drag surface, it has found widespread application in my country's aviation and aerospace sectors. Rocket sled tests can effectively meet the requirements for testing the performance of a drag parachute. The parachute's swing angle during rocket sled tests is a key performance indicator.

[0003] Currently, the drag parachute swing angle measurement in drag parachute rocket sled parachute jettisoning tests generally uses a precision turntable measurement method. During the measurement, two precision turntables are used to track the rocket sled and the drag parachute. The forward intersection method is used to solve the spatial coordinates of the end node of the main parachute rope and calculate the drag parachute swing angle. Each precision turntable contains a high-speed camera and a camera pitch and horizontal angle acquisition device. This method can measure the drag parachute swing angle value with high precision, but the equipment structure is complex and requires high tracking experience of technical personnel.

[0004] When calculating the swing angle of a parachute in a wind tunnel, two fixed cameras are generally used to measure the parachute's swing angle using the forward intersection method. However, the space on the rocket sled is limited, making it difficult to meet the intersection angle between the two cameras.

[0005] Another method for measuring the swing angle of the drag parachute is to use a monocular camera to treat the end node of the drag parachute's main parachute rope as a virtual point for iterative calculation, obtain the spatial coordinates of the end node of the drag parachute's main parachute rope, and then calculate the swing angle of the drag parachute. The process of calculating the coordinates of the end node of the drag parachute's main parachute rope through iterative calculation is complicated, but this method has a large amount of calculation and is difficult to meet the needs of use.

[0006] Therefore, a computationally simple method using a monocular camera is needed to measure the parachute swing angle. Summary of the Invention

[0007] The purpose of this application is to provide a method for measuring the parachute swing angle in a rocket sled drag parachute test, which saves the number of cameras and reduces the workload of swing angle calculation, thereby improving measurement efficiency.

[0008] This application is implemented as follows: The present application provides a method for measuring the parachute swing angle in a rocket sled drag parachute test, comprising the following steps: The camera is installed on the rocket sled to conduct a drag parachute test, and the camera is used to capture the motion trajectory of the end of the main parachute rope node of the drag parachute; Calibrate the camera to calculate the internal and external orientation elements of the camera; Calculate the real-world distance coordinates of the main line knot end; Calculate the image point coordinates of the main parachute line node end in the image space coordinate system with the camera projection center as the origin; Calculate the spatial coordinates of the image point at the end of the main parachute line node; The spatial straight line parameter equations of the camera projection center, the image point coordinates of the main parachute line node end, and the main parachute line node end have been calculated; Calculate the motion trajectory of the end of the main parachute line node; Calculate the pitch and horizontal angles of the drag parachute.

[0009] In some optional implementations, calibrating a camera to calculate the internal and external orientation elements of the camera includes the following steps: In the given object space coordinate system, the object point coordinates at the end of the main parachute rope node of the drag parachute are P ( X , Y , Z ), the coordinates of the camera's photography center are S ( X S , Y S , Z S ); In the selected image coordinate system c-xy, the coordinates of the principal point are o ( x 0, y 0), the image point coordinates are a ( x,y ), the focal length of the camera lens is f ; The orientation of the image in I-XYZ is ( f , oh , k ) definition, direction cosines ( a i , b i , c i , i =1,2,3) is( f , oh , k ) function; the distortion coefficient of the lens is ( w 1. w 2. k 1. k 2); Image point a The correction factor for the systematic error in the imaging process is (Δx, Δy). Based on the fact that the object point at the end of the main parachute rope node of the drag parachute, the image point, and the projection center of the camera are on a straight line in space, the collinearity condition equation is obtained: ; In the adjustment process, the unknowns are classified and the error equation based on the collinearity condition equation is obtained: ; Where V is the correction factor of the image point coordinates, X1, X2, and X3 are the correction factors of the exterior orientation elements, interior orientation elements, and distortion coefficients, respectively:

[0010] A i (i=1,2,3) is the matrix containing the coefficients, L is the constant in the formula: ; ; In the formula x’ 、 y’ is the calculated value of the previous iteration; The following calculation formula is obtained: ; By using the least squares solution, we can get: ; In calculating X Then find the internal and external orientation elements of the camera, including the focal length of the lens f 、The main point of the vehicle-mounted high-speed camera ( x 0, y 0), lens distortion coefficient ( w 1. w 2. k 1. k 2) The spatial coordinates of the photographic center of the vehicle-mounted high-speed camera (Xs, Ys, Zs) and the orientation of the image of the vehicle-mounted high-speed camera ( f , oh , k ).

[0011] In some optional embodiments, according to the measured image plane coordinates of the end of the main parachute line node along the heading direction and the length of a single pixel of the camera u Calculate the real-world distance coordinates of the end of the main parachute line node a’’ ( x , y ).

[0012] In some optional embodiments, the real world distance coordinates of the main parachute line node end are used. a’’ ( x , y ) and the focal length of the camera lens f Calculate the image point coordinates of the main parachute line node end in the image space coordinate system with the camera projection center as the origin.

[0013] In some optional embodiments, calculating the spatial coordinates of the image point at the end of the main parachute line node includes the following steps: Calculate the real-world distance coordinates of the end of the main parachute rope node with the center of the image as the origin based on the camera resolution of M*N a ( x i , y i ), spatial coordinates p’ ( x i , y i , -f ), image space auxiliary coordinates p’’ ( X i , Y i , Z i ), image space auxiliary coordinates of the main line node end p’’ The spatial coordinates of the image point at the end of the main parachute rope node are obtained by translation p ( X’ , Y’ , Z’ ): x i = x -M / 2*u; y i = y -N / 2*u; ; ; in, a i , b i , c i It is the 9 direction cosines composed of the exterior orientation elements calibrated by the on-board high-speed camera.

[0014] In some optional implementation schemes, after calculating the spatial linear parameter equation of the camera projection center, the image point coordinates of the main parachute line node end, and the main parachute line node end, the spatial coordinates of the camera projection center are obtained by camera calibration. S ( X S , Y S , Z S ), combined with the spatial coordinates of the image point at the end of the main parachute rope node at this time p ( Xm , Ym , Zm ), we can get the space straight line Sp The direction vector ( m , n , s ), then the camera projection center can be calculated S , image point coordinates p , the end of the main line knot P The parametric equation of a line in space: ; Where (X', Y', Z') is the space line passing through p or S point.

[0015] In some optional embodiments, when calculating the trajectory of the main line knot end: According to the camera projection center S , image point coordinates p , the end of the main line knot P The motion trajectory of the main parachute line node end is calculated by the intersection of the spatial straight line parameter equation and the motion trajectory of the main parachute line node end.

[0016] In some optional embodiments, the pitch angle J and horizontal angle K of the drag parachute are calculated according to the following formulas: J = Arcsin(Z / R); K=Arcsin(Y / R); Where R is the length of the main parachute line; Z and Y are the spatial coordinates P(X, Y, Z) of the end of the main parachute line node.

[0017] The beneficial effects of the present application are as follows: the method for measuring the parachute swing angle in a rocket sled drag parachute test provided by the present application is to install a camera on a rocket sled trolley to perform a parachute drop test, use the camera to capture the motion trajectory image of the end of the main parachute rope node of the parachute, then calibrate the camera to solve its internal and external orientation elements, use the collinearity condition equation, rotation matrix, and spatial coordinate translation to solve the image space coordinates of the end node of the main parachute rope of the parachute, and solve the intersection of the spatial straight line passing through the camera projection center and the main parachute rope image point and the end node of the main parachute rope of the parachute to obtain the spatial coordinates of the end node of the main parachute rope, and then calculate the pitch and horizontal swing angles of the parachute. Compared with the existing binocular camera measurement method, the method for measuring the parachute swing angle in a rocket sled drag parachute test provided by the present application saves the number of cameras and reduces the workload of swing angle calculation, thereby improving measurement efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 A schematic flow chart of a method for measuring the parachute swing angle in a rocket sled drag parachute test provided in an embodiment of the present application; Figure 2 A schematic diagram of a method for measuring the parachute swing angle in a rocket sled drag parachute test provided in an embodiment of the present application, wherein a camera is mounted on a rocket sled pulley to perform a drag parachute test; Figure 3 The method for measuring the parachute swing angle in the rocket sled drag parachute test provided in the embodiment of the present application includes the parameter equation of the spatial straight line passing through the camera projection center, the image point coordinates, the end of the main parachute rope node, and the intersection of the motion trajectory of the end of the main parachute rope node.

[0020] In the figure: 100, rocket sled pulley; 110, slide rail; 120, camera; 130, drag parachute; 140, main parachute line; 150, main parachute line node end; 160, parachute barrel; 170, parachute lock. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0022] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without creative work are within the scope of protection of the present application.

[0023] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0024] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the product of this application is typically placed when in use. These terms are intended only to facilitate the description of this application and simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0025] Furthermore, terms such as "horizontal," "vertical," and "overhanging" do not necessarily imply that a component must be absolutely horizontal or overhanging, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but rather that it can be slightly tilted.

[0026] It should also be noted that, in the description of this application, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0027] In this application, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Moreover, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0028] The following is a further detailed description of the characteristics and performance of the method for measuring the parachute swing angle in the rocket sled drag parachute test of the present application in conjunction with the embodiments.

[0029] like Figure 1 and Figure 2 As shown, the embodiment of the present application provides a method for measuring the parachute swing angle in a rocket sled drag parachute test, comprising the following steps: Step 1: Fix the camera 120 on the rocket sled sled 100, which is set on the slide rail 110, so that the image captured by the camera 120 covers the movement trajectory range of the main parachute rope node end 150 of the main parachute rope 140 on the drag parachute 130 connected to the rocket sled sled 100; before conducting the drag parachute parachute dropping test, adjust the camera trigger mode to the rising edge mode, and tie the camera trigger line to the slider at the bottom of the rocket sled sled 100. When the rocket sled sled 100 starts, cut the trigger line and the camera 120 starts recording. After the drag parachute 130 is dropped and the rocket sled sled 100 is stationary, connect the camera 120 and the computer via a data cable to download the movement video of the drag parachute 130 to the computer.

[0030] Step 2: Calibrate the camera to calculate the internal and external orientation elements of the camera; The camera 120 is calibrated within the swinging area of ​​the drag parachute 130. Multiple control points are evenly set within the swinging range of the drag parachute 130, and the image of each control point is captured by the camera 120. The spatial coordinates of each control point are calculated using a total station.

[0031] In a given object space coordinate system, the object point coordinate of the main parachute rope node end 150 of the drag parachute 130 is P ( X , Y , Z ), the photographic center coordinates of camera 120 are S ( X S , Y S , Z S ); In the selected image coordinate system c-xy, the intersection coordinates of the main optical axis of the camera 120 and the image plane, that is, the principal point coordinates are o ( x 0, y 0), the image point coordinates are a ( x,y ), the focal length of the camera 120 is f ; The orientation of the image in I-XYZ is ( f , oh , k ) definition, direction cosines ( a i , b i , c i , i =1,2,3) is( f , oh , k ) function; image point aThe correction factor for the systematic error in the imaging process is (Δx, Δy); The internal and external orientation elements of the camera 120 are calibrated using the bundle adjustment method. The coordinates of the image points of all control points are used as observation values ​​to calculate the best estimate. The principle of calculating the best estimate is to make the correction number V of each observation value satisfy V T V is the minimum.

[0032] The collinearity condition equation is derived based on the object point, the image point, and the projection center of the camera 120 at the end 150 of the main parachute line of the drag parachute 130 being on a straight line in space: ; In the adjustment process, the unknowns are classified and the error equation based on the collinearity condition equation is obtained: ; Where V is the correction factor of the image point coordinates, X 1. X 2. X 3 are the correction factors for exterior elements, interior elements and distortion coefficients respectively:

[0033] Where, A i (i=1,2,3) is the matrix containing the coefficients, L is the constant in the formula: ; ; Where, x’ 、 y’ is the calculated value of the previous iteration; This results in the following calculation formula: ; Solving the equation by the least squares method yields: ; In calculating X Then find the internal and external orientation elements of the camera, including the focal length of the lens f 、The main point of the vehicle-mounted high-speed camera ( x 0, y 0), lens distortion coefficient ( w 1. w 2. k 1. k 2), the spatial coordinates of the camera's photographic center (Xs, Ys, Zs) and the camera's image orientation ( f , oh, k ).

[0034] Step 3: Calculate the real-world distance coordinates of the main line node end. According to the measured image plane coordinates of the end 150 of the main parachute line node on the right side of the heading direction a’ ( x,y ) and the length of a single pixel of the camera u Calculate the real-world distance coordinates of the end of the main parachute line node 150 a’’ ( x , y ).

[0035] Step 4: Calculate the coordinates of the image point at the end of the main parachute line node in the image space coordinate system with the camera projection center as the origin; Based on the real-world distance coordinate of 150 from the end of the main parachute line node a’’ ( x , y ) and the focal length of the camera's 120 lens f Calculate the coordinates of the image point of the main parachute line node end 150 in the image space coordinate system with the projection center of the camera 120 as the origin; Step 5: Calculate the spatial coordinates of the image point at the end of the main parachute rope node; The real-world distance coordinates of the main parachute line node end 150° are calculated based on the resolution of the camera 120 being M*N and the center of the image being the origin. a ( x i , y i ), spatial coordinates p’ ( x i , y i , -f ), image space auxiliary coordinates p’’ ( X i , Y i , Z i ), image space auxiliary coordinates of the main parachute line node end 150 p’’ The spatial coordinates of the 150-degree image point at the end of the main parachute rope node are obtained by translation. p ( X’ , Y’ , Z’ ): x i = x -M / 2*u; y i = y -N / 2*u; ; ; in, a i , b i , c i are the nine direction cosines composed of the exterior orientation elements calibrated by the camera 120 .

[0036] Step 6: Calculate the spatial straight line parameter equation of the projection center of the camera 120, the image point coordinates of the main parachute line node end 150, and the main parachute line node end 150; After calculating the spatial linear parameter equations of the camera projection center, the image point coordinates at the end of the main parachute line node, and the end of the main parachute line node, the spatial coordinates of the camera projection center are obtained by camera calibration. S ( X S , Y S , Z S ), combined with the spatial coordinates of the image point at the end of the main parachute rope node at this time p ( X m , Y m , Z m ), we can get the space straight line Sp The direction vector ( m , n , s ), then the camera projection center can be calculated S , image point coordinates p , the end of the main line knot P The parametric equation of a line in space: ; Where (X', Y', Z') is the space line passing through p or S point.

[0037] Step 7: Calculate the motion trajectory of the end of the main parachute line node; From the collinearity condition equation, we can also know that the space straight line Sp Pass the end of the main line knot P , the length of the main parachute line 140 is R, and the end of the main parachute line node moves on a sphere with the main parachute line length as the sphere radius and the parachute lock 170 in the parachute barrel 160 as the sphere center. At this time, the motion trajectory equation of the main parachute line node end is as follows: (X-X0) 2 +(Y-Y0) 2+(Z-Z0) 2 =R 2 ; Wherein, P(X, Y, Z) is the spatial coordinate of the end 150 of the main parachute line node, A(X0, Y0, Z0) is the spatial coordinate of the parachute lock 170 in the parachute barrel 160 of the drag parachute 130, and R is the length of the main parachute line 140.

[0038] According to the camera 120 projection center S , image point coordinates p , the end of the main line knot P The motion trajectory of the end of the main parachute line node is calculated by the intersection of the spatial straight line parameter equation and the motion trajectory of the end of the main parachute line node: The spatial straight line passing through the projection center S of the camera 120, the object point P at the end of the main parachute rope node, and the image point p at the end of the main parachute rope node intersects the sphere with the main parachute rope length AP as the radius and the parachute barrel node A as the center at points P and F, as shown in the following example: Figure 3 As shown in Figure 1 . A is the spatial coordinate of the parachute lock 170 in the parachute barrel, p is the spatial coordinate of the image point, P is the spatial coordinate of the end of the main parachute line knot, and S is the camera projection center. The camera captures the motion of the drag parachute line knot, showing that when the drag parachute main parachute line moves, the X value of the end of the main parachute line knot is positive. Therefore, P is the real spatial position of the drag parachute main parachute line, and the spatial coordinates P (X, Y, Z) of the main parachute line can be obtained.

[0039] Step 8: Calculate the pitch angle and horizontal swing angle of the drag parachute 130.

[0040] The pitch angle J and horizontal angle K of the drag parachute 130 are calculated according to the following formula: J = Arcsin(Z / R); K=Arcsin(Y / R); Where R is the length of the main parachute line; Z and Y are the spatial coordinates P(X, Y, Z) of the end of the main parachute line node.

[0041] The method provided in this application for measuring the parachute swing angle in a rocket sled drag parachute test is to install a camera on a rocket sled to perform a parachute drop test, use the camera to capture the motion trajectory image of the end of the main parachute rope node of the parachute, then calibrate the camera to solve its internal and external orientation elements, use the collinearity condition equation, rotation matrix, and spatial coordinate translation to solve the image space coordinates of the end node of the main parachute rope of the parachute, and solve the intersection of the spatial straight line passing through the camera projection center and the image point of the main parachute rope and the end node of the main parachute rope to obtain the spatial coordinates of the end node of the main parachute rope, and then calculate the pitch and horizontal swing angles of the parachute. Compared with the existing binocular camera measurement method, the method provided in this application for measuring the parachute swing angle in a rocket sled drag parachute test saves the number of cameras and reduces the workload of swing angle calculation, thereby improving measurement efficiency.

[0042] Example 1 The present invention provides a method for measuring the parachute swing angle in a rocket sled drag parachute test, comprising the following steps: Step 1: Fix the camera 120 on the rocket sled sled 100, which is set on the slide rail 110, so that the image captured by the camera 120 covers the movement trajectory range of the main parachute rope node end 150 of the main parachute rope 140 on the drag parachute 130 connected to the rocket sled sled 100; before conducting the drag parachute parachute dropping test, adjust the camera trigger mode to the rising edge mode, and tie the camera trigger line to the slider at the bottom of the rocket sled sled 100. When the rocket sled sled 100 starts, cut the trigger line and the camera 120 starts recording. After the drag parachute 130 is dropped and the rocket sled sled 100 is stationary, connect the camera 120 and the computer via a data cable to download the movement video of the drag parachute 130 to the computer.

[0043] Step 2: calibrate the camera 120 within the swinging area of ​​the drag parachute 130 to calculate its internal and external orientation elements.

[0044] Nine control points are evenly spaced within the swing range of the main parachute cord node 150 of the drag parachute 130. Camera 120 captures images of these nine control points. A total station is used to calculate the spatial coordinates of the nine control points and the parachute lock 170 of the drag parachute 130. The internal and external orientation elements of camera 120 are calibrated using bundle adjustment.

[0045] Calculate the focal length of the camera 120 lens as f =8.316375mm, the intersection coordinates of the principal optical axis of the camera 120 and the image plane o (-0.34587939,0.21597052), the distortion coefficient of the camera 120 lens (-1.0630795672*10 -4 、-3.1784260845*10 -5、3.0381213199*10 -3 、-2.7487576875*10 -5 ), the spatial coordinates of the camera 120 photography center S (-1480.191385, 1844.741402, 794.8143401) and image orientation (φ, ω, κ) = (-1.61125574, 0.18529013, -0.00855991).

[0046] Step 3: Calculate the real-world distance coordinates of the main line knot end. With the image center at (0,0), the camera 120 resolution is 2048*2048, and the single pixel length of camera 120 is 12μm. When the canopy is fully inflated, the 150-pixel coordinates of the right parachute's main line knot end along the heading direction are (-601.75, -241.25). The real-world distance coordinates of the main line knot end, a'' (-7.221, -2.895), can be calculated.

[0047] Step 4: Calculate the coordinates of the image point at the end of the main parachute rope node in the image space coordinate system with the camera projection center as the origin. According to the calibration of camera 120, the focal length of camera 120 is f =8.3mm, then the image space coordinates of the end 150 of the drag parachute main line node in the image space coordinate system with the camera projection center as the origin are p'(-7.221, -2.895, -8.316375).

[0048] Step 5: Calculate the spatial coordinates of the image point at the end of the drag parachute's main parachute knot. Calculate the auxiliary image space coordinates p'' (Xi, Yi, Zi) of the image point at the end of the drag parachute's main parachute knot based on the rotation matrix calibrated in Step 2. The image space auxiliary coordinates are translated to obtain the real space coordinates p (X', Y', Z') of the image point at the end of the drag parachute's main parachute knot.

[0049] Step 6: Calculate the parametric equation of the spatial line passing through the camera projection center S, the image point coordinates p at the end of the main parachute rope node, and the end of the main parachute rope node P.

[0050] The spatial coordinates of the camera projection center are obtained by camera calibration as S ( X S , Y S , Z S ), the spatial coordinates of the image point at the end 150 of the main parachute line node are p ( X m , Y m , Zm ), we can get the space straight line Sp The direction vector ( m , n , s ), calculate the camera projection center S , image point coordinates p , the end of the main line knot P The parametric equation of a line in space: ; Among them, (X, Y, Z) is any point on the space line, (X', Y', Z') is the point where the space line passes. p or S point.

[0051] Step seven, find the motion trajectory of the end of the main parachute rope node; solve the intersection of the motion trajectory of the end of the main parachute rope node and the spatial straight line passing through the camera projection center S, the image point coordinate p, and the end of the main parachute rope node P.

[0052] From the collinearity condition equation, we can also know that the space straight line Sp Pass the end of the main line knot P The main line 140 is 4.2 m long, i.e., R = 4.2 m. The end of the main line knot moves on a sphere with the main line length as the radius and the parachute lock 170 in the umbrella barrel 160 as the center. At this time, the motion trajectory equation of the main line knot end is as follows: (X-X0) 2 +(Y-Y0) 2 +(Z-Z0) 2 =R 2 ; Wherein, P(X, Y, Z) is the spatial coordinate of the end 150 of the main parachute line node, A(X0, Y0, Z0) is the spatial coordinate of the parachute lock 170 in the parachute barrel 160 of the drag parachute 130, and R is the length of the main parachute line 140.

[0053] According to the camera 120 projection center S , image point coordinates p , the end of the main line knot P The intersection of the parametric equation of the space line and the motion trajectory of the main parachute rope node end is used to calculate the motion trajectory of the main parachute rope node end. It can be seen that the intersection of the space line passing through the camera projection center S, the object point P 150 degrees from the end of the drag parachute main parachute rope node end, and the image point p of the main parachute rope node end and the sphere with the main parachute rope length AP as the radius and the parachute lock A in the parachute barrel as the sphere center is P and F, as shown in the following example: Figure 3As shown in the figure. A is the parachute lock inside the parachute barrel, p is the real space coordinate of the image point, P is the spatial coordinate of the end of the main parachute rope knot, and S is the projection center of the high-speed camera. From the camera's capture of the motion of the drag parachute rope knot, we can see that when the drag parachute main parachute rope moves, the X value of the end of the main parachute rope knot is positive. Therefore, P is the real space position of the drag parachute main parachute rope, and the spatial coordinates P(X, Y, Z) of the main parachute rope can be obtained.

[0054] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A method for measuring the parachute swing angle in a rocket sled drag parachute test, characterized in that: The following steps are involved: A camera is mounted on a rocket sled to perform a drag parachute drop test, and a motion trajectory image of the end of the main parachute rope node of the drag parachute is captured by the camera; Calibrate the camera to calculate the internal and external orientation elements of the camera; Calculating the real-world distance coordinate of the end of the main line node; Calculating the coordinates of the image point of the end of the main parachute line node in the image space coordinate system with the camera projection center as the origin; Calculating the spatial coordinates of the image point at the end of the main parachute line node; The spatial straight line parameter equations of the camera projection center, the image point coordinates of the main parachute line node end, and the main parachute line node end have been calculated; Calculating the motion trajectory of the end of the main parachute line node; The pitch angle and horizontal angle of the drag parachute are calculated.

2. The method for measuring the parachute swing angle in the rocket sled drag parachute test according to claim 1, characterized in that: Calibration of the camera to calculate the internal and external orientation elements of the camera includes the following steps: In the given object space coordinate system, the object point coordinates of the end of the main parachute rope node of the drag parachute are P ( X , Y , Z ), the coordinates of the camera's photography center are S ( X S , Y S , Z S ); In the selected image coordinate system c-xy, the coordinates of the principal point are o ( x 0, y 0), the image point coordinates are a ( x,y ), the focal length of the camera lens is f ; The orientation of the image in I-XYZ is ( φ , ω , κ ) definition, direction cosines ( a i , b i , c i , i =1,2,3) is( φ , ω , κ ) function; the distortion coefficient of the lens is ( w 1. w 2. k 1. k 2); Image point a The correction factor for the system error in the imaging process is (Δx, Δy). The collinearity condition equation is derived based on the object point at the end of the main parachute rope node of the drag parachute, the image point and the projection center of the camera being on a straight line in space: ； In the adjustment process, the unknowns are classified and the error equation based on the collinearity condition equation is obtained: ； Where V is the correction factor of the image point coordinates, X1, X2, and X3 are the correction factors of the exterior orientation elements, interior orientation elements, and distortion coefficients, respectively: A i (i=1,2,3) is the matrix containing the coefficients, L is the constant in the formula: ； ； In the formula x’ 、 y’ is the calculated value of the previous iteration; The following calculation formula is obtained: ； By using the least squares solution, we can get: ； In calculating X Then find the internal and external orientation elements of the camera, including the focal length of the lens f 、The main point of the vehicle-mounted high-speed camera ( x 0. y 0), lens distortion coefficient ( w 1. w 2. k 1. k 2), the spatial coordinates of the photographic center of the vehicle-mounted high-speed camera (Xs, Ys, Zs) and the orientation of the image of the vehicle-mounted high-speed camera ( φ , ω , κ ).

3. The method for measuring the parachute swing angle in the rocket sled drag parachute test according to claim 2, characterized in that: According to the measured image plane coordinates of the end of the main parachute line node along the heading direction and the length of a single pixel of the camera u Calculate the real-world distance coordinates of the end of the main parachute line node a’’ ( x , y ).

4. The method for measuring the parachute swing angle in a rocket sled drag parachute test according to claim 2, characterized in that: According to the real world distance coordinates of the end of the main parachute line node a’’ ( x , y ) and the focal length of the camera lens f Calculate the image point coordinates of the main parachute line node end in the image space coordinate system with the camera projection center as the origin.

5. The method for measuring the parachute swing angle in a rocket sled drag parachute test according to claim 2, characterized in that: Calculating the spatial coordinates of the image point at the end of the main parachute line node includes the following steps: Calculate the real-world distance coordinates of the end of the main parachute line node with the center of the image as the origin based on the camera resolution of M*N a ( x i , y i ), spatial coordinates p’ ( x i , y i , -f ), image space auxiliary coordinates p’’ ( X i , Y i , Z i ), image space auxiliary coordinates of the main line node end p’’ The spatial coordinates of the image point at the end of the main parachute rope node are obtained by translation p ( X’ , Y’ , Z’ ): x i = x -M / 2*u; y i = y -N / 2*u; ； ； in, a i , b i , c i It is the 9 direction cosines composed of the exterior orientation elements calibrated by the on-board high-speed camera.

6. The method for measuring the parachute swing angle in a rocket sled drag parachute test according to claim 4, characterized in that: After calculating the spatial linear parameter equations of the camera projection center, the image point coordinates at the end of the main parachute line node, and the end of the main parachute line node, the spatial coordinates of the camera projection center are obtained by camera calibration. S ( X S , Y S , Z S ), combined with the spatial coordinates of the image point at the end of the main parachute rope node at this time p ( Xm , Ym , Zm ), we can get the space straight line Sp The direction vector ( m , n , s ), then the camera projection center can be calculated S , image point coordinates p , the end of the main line knot P The parametric equation of a line in space: ； Where (X', Y', Z') is the space line passing through p or S point.

7. The method for measuring the parachute swing angle in a rocket sled drag parachute test according to claim 6, characterized in that: When calculating the motion trajectory of the end of the main parachute line node: according to the camera projection center S , image point coordinates p , the end of the main line knot P The motion trajectory of the main parachute line node end is calculated by the intersection of the spatial straight line parameter equation and the motion trajectory of the main parachute line node end.

8. The method for measuring the parachute swing angle in a rocket sled drag parachute test according to claim 7, characterized in that: The pitch angle J and horizontal angle K of the drag parachute are calculated according to the following formula: J = Arcsin(Z / R); K=Arcsin(Y / R); Where R is the length of the main line; Z and Y are the spatial coordinates P(X, Y, Z) of the end of the main line node.

Images