Strap-down infrared seeker digital platform image stabilization method

Abstract

The invention provides a strapdown infrared seeker digital platform image stabilization method, and the method comprises the steps: obtaining an attitude change angle between aircraft body coordinate systems corresponding to the exposure moments of a current frame image and a next frame image, and an included angle between a current frame target in the aircraft body coordinate systems and a longitudinal axis of an aircraft; the prediction position of the next frame of target in the image is calculated, reference is provided for a target tracking algorithm to move the template position, the tracking capability of the strapdown infrared seeker is improved, and tracking loss is avoided.

Description

Technical Field

[0001] The present application relates to the field of optoelectronic tracking technology, and in particular to a strapdown infrared seeker digital platform image stabilization method. Background Art

[0002] The strapdown infrared seeker is an advanced guidance technology component. With its high precision, high reliability and fast response, it provides important support for the navigation, guidance and control of various aircraft and spacecraft in the aerospace field. In the technical solutions related to the strapdown infrared seeker, the operational process of target recognition and tracking is involved. First, in the recognition process, the real-time image collected by the infrared seeker is matched with a large reference image to determine the position of the target in the real-time image. However, the recognition process takes a long time and has poor real-time performance, so tracking operations are still required in practical applications. In the tracking link, in order to improve real-time performance, a small template is selected with the tracking point of the previous frame in the real-time image as the center, and the target is only searched within the range of this small template.

[0003] During operation, the strapdown infrared seeker cannot stabilize the image through the servo platform, so it cannot guarantee that the target is always near the center of the image. When the angular velocity of the aircraft's attitude motion is large, the target moves faster on the image, so in the next frame the target may move out of the tracking template range, resulting in tracking loss. Summary of the invention

[0004] In view of the above defects or deficiencies in the prior art, the present application aims to provide a strapdown infrared seeker digital platform image stabilization method, comprising the following steps: S100. Obtaining the attitude change angle between the aircraft body coordinate system corresponding to the exposure time of the current frame image and the next frame image, and setting it as the first rotation angle; S200. Obtaining the angle of the current frame target relative to the longitudinal axis of the aircraft in the aircraft body coordinate system, recorded as a first sight angle, wherein the first sight angle includes a first heading sight angle and a first pitch sight angle of the current frame target relative to the longitudinal axis of the aircraft; S300. Calculate the position of the target in the next frame in the image according to the first sight angle and the first rotation angle, and record it as the predicted position.

[0005] According to the technical solution provided in the embodiment of the present application, step S300 includes the following steps: S310. Calculate the angle of the next frame target relative to the longitudinal axis of the aircraft in the aircraft body coordinate system according to the first sight angle and the first rotation angle, which is recorded as the second sight angle, wherein the second sight angle includes a second heading sight angle and a second pitch sight angle of the next frame target relative to the longitudinal axis of the aircraft; S320. Convert the second sight angle to the imager body coordinate system of the strapdown infrared seeker to obtain a third sight angle, wherein the third sight angle includes a third heading sight angle and a third elevation sight angle of the next frame target relative to the imager; S330. Calculate the angle of the target in the next frame in the image according to the third sight angle, and record it as the predicted angle; S340. Calculate the predicted position according to the predicted angle.

[0006] According to the technical solution provided in the embodiment of the present application, step S100 includes the following steps: S110. Obtaining the coordinate components of the aircraft attitude angular velocity in the aircraft body coordinate system; S120. According to the Longo Kutta integration strategy, the first rotation angle is calculated according to the coordinate components.

[0007] According to the technical solution provided in the embodiment of the present application, step S120 includes the following steps: S121. Set the initial rotation angle; S122. constructing a differential equation, wherein the differential equation is used to characterize the relationship between the coordinate component, the first rotation angle, and the first rotation angular velocity, wherein the first rotation angular velocity is obtained by differentiating the first rotation angle; S123. According to the initial rotation angle, the differential equation is iteratively calculated to obtain a first rotation angle within a set time.

[0008] According to the technical solution provided in the embodiment of the present application, step S310 includes the following steps: S311. construct a first conversion matrix according to the first sight line angle and the first rotation angle, wherein the first conversion matrix is ​​a rotation matrix from the body sight line coordinate system of the current frame to the aircraft body coordinate system of the next frame; S312. Calculate the second sight angle according to the first transformation matrix.

[0009] According to the technical solution provided in the embodiment of the present application, step S312 includes the following steps: S3121. construct the first transformation matrix according to the second sight line angle and the second rotation angle, wherein the second rotation angle is the rotation angle of the next frame body sight line coordinate system relative to the current frame body sight line coordinate system; S3122. Calculate the value of the second sight angle based on the equivalent relationship.

[0010] According to the technical solution provided in the embodiment of the present application, step S320 includes the following steps: S321. Construct a second transformation matrix according to the second sight line angle and the third transformation matrix, wherein the second transformation matrix is ​​a rotation matrix from the body sight line coordinate system to the imager body coordinate system, and the third transformation matrix is ​​a rotation matrix from the aircraft body coordinate system to the imager body coordinate system; S322. Calculate the third sight angle according to the second transformation matrix.

[0011] According to the technical solution provided in the embodiment of the present application, step S322 includes the following steps: S3221. Construct the second conversion matrix according to the third sight angle; S3222. Calculate the value of the third sight angle based on the equivalent relationship.

[0012] In summary, the present application proposes a method for stabilizing the image of a strapdown infrared seeker digital platform, which obtains the attitude change angle between the aircraft body coordinate system corresponding to the exposure time of the current frame image and the next frame image, and the angle between the current frame target in the aircraft body coordinate system and the longitudinal axis of the aircraft, and calculates the predicted position of the next frame target in the image, provides a reference for the moving template position of the target tracking algorithm, improves the tracking capability of the strapdown infrared seeker, and avoids tracking loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A flow chart of a strapdown infrared seeker digital platform image stabilization method provided in an embodiment of the present application; Figure 2 A curve showing the actual value of the heading target position and the predicted value of the heading target position changing over time provided in an embodiment of the present application; Figure 3 This is a curve showing the change of the actual value of the pitch target position and the predicted value of the pitch target position over time provided in an embodiment of the present application. DETAILED DESCRIPTION

[0014] The present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant inventions, rather than to limit the inventions. It should also be noted that, for ease of description, only the parts related to the invention are shown in the accompanying drawings.

[0015] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0016] As mentioned in the technical problem of the background technology, the present application proposes a strapdown infrared seeker digital platform image stabilization method, comprising the following steps: S100. Obtaining the attitude change angle between the aircraft body coordinate system corresponding to the exposure time of the current frame image and the next frame image, and setting it as the first rotation angle; In actual scenes, the target's position change between the two frames can be obtained by integrating the target's movement speed between the two frames. The target's movement speed in the image cannot be directly obtained, but it is approximately equal to the inertial line of sight angular velocity of the aircraft and the target minus the aircraft's attitude motion angular velocity. The line of sight angular velocity integration can be used to calculate the target's position change in the image caused by the relative motion of the aircraft's center of mass and the target. Since the line of sight angular velocity value before divergence is small, the impact on the target's position change within the time interval between the two frames of images is generally no more than 2 pixels and can be ignored. The aircraft attitude motion angular velocity integration can be used to calculate the target's position change in the image caused by the aircraft's attitude motion. This is the main influencing factor of the target's position change in the image, so this scheme uses the aircraft's attitude change to predict the position of the next frame of the target in the image.

[0017] Step S100 includes the following steps: S110. Obtaining the coordinate components of the aircraft attitude angular velocity in the aircraft body coordinate system; Among them, the aircraft body coordinate system is a commonly used coordinate system to describe the motion state of the aircraft, with the center of mass of the aircraft as the origin, the X-axis along the axis of the aircraft fuselage, pointing to the direction of the nose as positive; the Y-axis is perpendicular to the X-axis in the symmetry plane of the aircraft, pointing upward as positive; the Z-axis is perpendicular to the symmetry plane of the aircraft, and its direction is determined according to the right-hand rule.

[0018] Optionally, the angular velocity of the aircraft around the three coordinate axes in the aircraft body coordinate system can be directly measured by a gyroscope to obtain coordinate components. Other technologies that can obtain coordinate components can also be used. These are existing technologies and will not be described in detail here.

[0019] S120. According to the Longo Kutta integration strategy, the first rotation angle is calculated according to the coordinate components; comprising the following steps: S121. Set the initial rotation angle; S122. Construct a differential equation, wherein the differential equation is used to characterize the relationship between the coordinate component, the first rotation angle, and the first rotation angular velocity, wherein the first rotation angular velocity is obtained by differentiating the first rotation angle; wherein the differential equation is as shown below: Formula (1) in: , , is the component of the aircraft attitude angular velocity in the aircraft body coordinate system; , , is the first rotation angle between the aircraft body coordinate systems corresponding to the exposure moments of the previous and next two images; , , is the differential of the rotation angle.

[0020] S123. According to the initial rotation angle, the differential equation is iterated to obtain a first rotation angle within a set time; The present application calculates the first rotation angle by the fourth-order Runge Kutta method, and the calculation formula of the fourth-order Runge Kutta method is as follows: Formula (2) In the formula, i is the sampling time, is the differential equation; and , h is the iteration step length.

[0021] S200. Obtaining the angle of the current frame target relative to the longitudinal axis of the aircraft in the aircraft body coordinate system, recorded as a first sight angle, wherein the first sight angle includes a first heading sight angle and a first pitch sight angle of the current frame target relative to the longitudinal axis of the aircraft; The position of the target in the current frame can be obtained according to the recognition and tracking algorithm, and then the first heading sight angle can be obtained by calculation. and the first pitch sight angle , S300. Calculating the position of the target in the next frame in the image according to the first sight angle and the first rotation angle, recorded as the predicted position; comprising the following steps: S310. Calculate the angle of the next frame target relative to the longitudinal axis of the aircraft in the aircraft body coordinate system according to the first sight angle and the first rotation angle, which is recorded as the second sight angle, wherein the second sight angle includes the second heading sight angle and the second pitch sight angle of the next frame target relative to the longitudinal axis of the aircraft; comprising the following steps: S311. construct a first conversion matrix according to the first sight line angle and the first rotation angle, wherein the first conversion matrix is ​​a rotation matrix from the body sight line coordinate system of the current frame to the aircraft body coordinate system of the next frame; Among them, the origin of the body line of sight coordinate system is the same as that of the aircraft body coordinate system, located at the center of mass of the aircraft, the X-axis is the direction of the line connecting the aircraft and the target, pointing to the target is positive, the Y-axis is the heading axis, and the Z-axis is the pitch axis. The coordinate system is obtained by rotating the heading line of sight angle and the pitch line of sight angle of the aircraft body coordinate system.

[0022] The first conversion matrix can be expressed as: Formula (3) In the formula, represents the first heading sight angle, Represents the first pitch sight angle; S312. Calculating the second sight angle according to the first transformation matrix; comprising the following steps: S3121. construct the first transformation matrix according to the second sight line angle and the second rotation angle, wherein the second rotation angle is the rotation angle of the next frame body sight line coordinate system relative to the current frame body sight line coordinate system; Among them, the present invention only considers the rotation of the stereoscopic line of sight coordinate system. Since the influence of the target position change in the time interval between the two frames of images generally does not exceed 2 pixels, the relative motion between the aircraft and the target is not considered, that is, the line of sight does not move, and only the rotation of the stereoscopic line of sight coordinate system is considered; The first conversion matrix can also be expressed as follows: Formula (4) In the formula, is the second heading sight angle, is the second pitch sight angle; is the second rotation angle.

[0023] S3122. Calculate the value of the second sight angle according to the equivalent relationship; Since the left sides of formula (3) and formula (4) are the same, according to the equivalence relationship, the right sides are also the same, and the second sight angle is calculated as: . S320. Convert the second sight angle to the imager body coordinate system of the strapdown infrared seeker to obtain a third sight angle, wherein the third sight angle includes a third heading sight angle and a third elevation sight angle of the next frame target relative to the imager; The strapdown infrared seeker uses its internal imager to detect infrared radiation emitted by the target. The origin of the imager body coordinate system is the same as the aircraft body coordinate system, located at the center of mass of the aircraft. The coordinate system is obtained by rotating the aircraft body coordinate system by a certain installation angle. The following steps are included: S321. Construct a second transformation matrix according to the second sight line angle and the third transformation matrix, wherein the second transformation matrix is ​​a rotation matrix from the body sight line coordinate system to the imager body coordinate system, and the third transformation matrix is ​​a rotation matrix from the aircraft body coordinate system to the imager body coordinate system; The second conversion matrix is ​​shown as follows: Formula (5) In the formula, L 2 is the second transformation matrix; L DTOCis the third conversion matrix; obtaining the third conversion matrix through the installation angle is a prior art and will not be described in detail here; S322. Calculating the third sight angle according to the second transformation matrix; comprising the following steps: S3221. Construct the second conversion matrix according to the third sight angle; The second conversion matrix can also be expressed as follows: Formula (6) In the formula, represents the third heading sight angle, Represents the third elevation viewing angle.

[0024] S3222. Calculate the third sight angle based on the equivalent relationship.

[0025] Since the left sides of the equal signs in formula (5) and formula (6) are the same, the right sides are also equal. According to the corresponding relationship of the matrices, we get:

[0026] S330. Calculate the angle of the target in the next frame in the image according to the third sight angle, and record it as the predicted angle; Assuming that the order of sight angle conversion is heading first, then pitch, the angle is calculated by the following formula: Formula (7) In the formula, Represents the angle of the target relative to the horizontal direction, Represents the angle of the target relative to the vertical direction.

[0027] S340. Calculate the predicted position according to the predicted angle; The predicted angle is converted into pixel coordinates in an imager coordinate system, wherein the origin of the imager coordinate system is usually located at the upper left corner of the imager, horizontally to the right is the positive direction of the X axis, and vertically downward is the positive direction of the Y axis.

[0028] Assuming that the number of pixels of the infrared imager is 512 in heading and 640 in elevation, the predicted position is calculated by the following formula: Formula (8) In the formula, Indicates the heading field of view of the infrared seeker, Indicates the pitch field angle; Represents the predicted value of the heading target position; Represents the predicted value of the pitch target position.

[0029] In summary, the present application calculates the predicted position of the next frame target in the image by obtaining the attitude change angle between the aircraft body coordinate system corresponding to the exposure time of the current frame image and the next frame image, and the angle between the current frame target and the longitudinal axis of the aircraft in the aircraft body coordinate system, so as to provide a reference for the position of the moving template of the target tracking algorithm, improve the tracking capability of the strapdown infrared seeker, and avoid tracking loss; in addition, the present application improves the prediction accuracy through the Longo Kutta method and coordinate system transformation. By comparing the predicted position calculated according to the present invention with the actual tracking result, the change of the predicted position and the actual value over time can be obtained, such as Figure 2 and Figure 3 As shown, the ordinate represents the position in pixels, and the abscissa represents time. The experimental results show that the method of the present invention has a good effect, the target position prediction accuracy is in line with expectations, and the tracking capability of the strapdown infrared seeker can be effectively improved.

[0030] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features are replaced with (but not limited to) technical features with similar functions disclosed in the present application.

Claims

1. A strapdown infrared seeker digital platform image stabilization method, characterized in that: The steps include: S100. Obtaining the attitude change angle between the aircraft body coordinate system corresponding to the exposure time of the current frame image and the next frame image, and setting it as the first rotation angle; S200. Obtaining the angle of the current frame target relative to the longitudinal axis of the aircraft in the aircraft body coordinate system, recorded as a first sight angle, wherein the first sight angle includes a first heading sight angle and a first pitch sight angle of the current frame target relative to the longitudinal axis of the aircraft; S300. Calculate the position of the target in the next frame in the image according to the first sight angle and the first rotation angle, and record it as the predicted position.

2. The strapdown infrared seeker digital platform image stabilization method according to claim 1, characterized in that: Step S300 includes the following steps: S310. Calculate the angle of the next frame target relative to the longitudinal axis of the aircraft in the aircraft body coordinate system according to the first sight angle and the first rotation angle, which is recorded as the second sight angle, wherein the second sight angle includes a second heading sight angle and a second pitch sight angle of the next frame target relative to the longitudinal axis of the aircraft; S320. Convert the second sight angle to the imager body coordinate system of the strapdown infrared seeker to obtain a third sight angle, wherein the third sight angle includes a third heading sight angle and a third elevation sight angle of the next frame target relative to the imager; S330. Calculate the angle of the target in the next frame in the image according to the third sight angle, and record it as the predicted angle; S340. Calculate the predicted position according to the predicted angle.

3. The strapdown infrared seeker digital platform image stabilization method according to claim 1, characterized in that: Step S100 includes the following steps: S110. Obtaining the coordinate components of the aircraft attitude angular velocity in the aircraft body coordinate system; S120. According to the Longo Kutta integration strategy, the first rotation angle is calculated according to the coordinate components.

4. The strapdown infrared seeker digital platform image stabilization method according to claim 3, characterized in that: Step S120 includes the following steps: S121. Set the initial rotation angle; S122. Constructing a differential equation, wherein the differential equation is used to characterize the relationship between the coordinate component, the first rotation angle, and the first rotation angular velocity, wherein the first rotation angular velocity is obtained by differentiating the first rotation angle; S123. According to the initial rotation angle, the differential equation is iteratively calculated to obtain a first rotation angle within a set time.

5. The strapdown infrared seeker digital platform image stabilization method according to claim 2, characterized in that: Step S310 includes the following steps: S311. construct a first conversion matrix according to the first sight line angle and the first rotation angle, wherein the first conversion matrix is ​​a rotation matrix from the body sight line coordinate system of the current frame to the aircraft body coordinate system of the next frame; S312. Calculate the second sight angle according to the first transformation matrix.

6. The strapdown infrared seeker digital platform image stabilization method according to claim 5, characterized in that: Step S312 includes the following steps: S3121. construct the first transformation matrix according to the second sight line angle and the second rotation angle, wherein the second rotation angle is the rotation angle of the next frame body sight line coordinate system relative to the current frame body sight line coordinate system; S3122. Calculate the value of the second sight angle based on the equivalent relationship.

7. The strapdown infrared seeker digital platform image stabilization method according to claim 2, characterized in that: Step S320 includes the following steps: S321. Construct a second transformation matrix according to the second sight line angle and the third transformation matrix, wherein the second transformation matrix is ​​a rotation matrix from the body sight line coordinate system to the imager body coordinate system, and the third transformation matrix is ​​a rotation matrix from the aircraft body coordinate system to the imager body coordinate system; S322. Calculate the third sight angle according to the second transformation matrix.

8. The strapdown infrared seeker digital platform image stabilization method according to claim 7, characterized in that: Step S322 includes the following steps: S3221. Construct the second conversion matrix according to the third sight angle; S3222. Calculate the value of the third sight angle based on the equivalent relationship.

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