A method and system for joint adjustment of optical image and laser altimetry data

Abstract

The present invention relates to a method and system for the joint adjustment of optical images and laser altimetry data. The method comprises the following steps: acquiring image data to establish a strict optical image model, and converting the rectangular coordinates in the imaging model into geodetic coordinates; incorporating a systematic error affine model into the imaging model, and using a dither harmonic function in the compensation function to compensate for low-order systematic errors; introducing a tie point error equation, an elevation control point error equation, and a virtual control point error equation to establish a normal equation, employing a strategy of eliminating variables to modify the normal equation for solution, eliminating the object coordinate correction, constructing a new modified normal equation, and performing adjustment calculations to obtain systematic error compensation parameters. Compared with the prior art, the present invention can effectively compensate for the effects of satellite platform dither and improve the elevation positioning accuracy of images.

Description

Technical Field

[0001] The present invention relates to, and in particular to, a method and system for combining optical image and laser altimetry data. Background Art

[0002] Remote sensing, as a non-contact object detection technology, has enormous application value both on Earth and in deep space. High-resolution cameras and laser altimetry are the two primary payloads carried by satellites for mapping. With technological advancements, the resolution of satellite imagery continues to improve, and laser altimetry data is also gradually improving towards higher density and a smaller footprint. During satellite operation, positioning errors are caused by various factors, and ground control points are generally used to correct for these systematic errors in the imagery. In the absence of ground control points, the high elevation accuracy of laser altimetry can be exploited, using the elevation values ​​of laser points as a control to correct for systematic errors in optical imagery and improve elevation positioning accuracy. Satellite platform flutter is a phenomenon of minute vibrations during satellite operation that can introduce periodic systematic errors, impacting positioning accuracy and high-precision mapping. The higher the image resolution, the more significant the impact of flutter. Summary of the Invention

[0003] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a method and system for the joint adjustment of optical images and laser altimetry data. For the joint adjustment of high-resolution images with vibration and laser altimetry data, vibration compensation is added to the adjustment process to improve the image elevation positioning accuracy, which has important theoretical significance and practical value.

[0004] The purpose of the present invention can be achieved by the following technical solutions:

[0005] A method for joint adjustment of optical image and laser altimetry data comprises the following steps:

[0006] S1. Acquire image data to establish a strict optical image model, and convert the rectangular coordinates in the imaging model into geodetic coordinates;

[0007] S2. Add the system error affine model compensation to the imaging model, and use the flutter harmonic function in the compensation function to compensate for the low-order system error. The expression of the compensated imaging model is:

[0008]

[0009] Among them, v x and v y is the image point coordinate residual, x and y are the focal plane coordinates of the image point, f1 and f2 are the image compensation functions, a i 、ω i 、 ai’ 、ω i '、 is the vibration harmonic function parameter, b i 、c i and d i is the affine model parameter, n is the number of flutter harmonic functions;

[0010] S3. Introduce the connection point error equation, the elevation control point error equation and the virtual control point error equation to establish the normal equation, adopt the strategy of eliminating variables and modifying the normal equation to solve it, eliminate the object coordinate correction, construct a new modified normal equation and then perform adjustment calculation to obtain the system error compensation parameters.

[0011] Furthermore, the connection point error equation is expressed as:

[0012]

[0013] Among them, v x and v y is the image point coordinate residual, B is the geodetic longitude, L is the geodetic latitude, H is the distance from the ground point to the center of the reference ellipsoid, F and G are the functions in S2, and F0 and G0 are the approximate values ​​after substituting the current parameter values ​​into the function.

[0014] Furthermore, the error equation of the elevation control point is expressed as:

[0015]

[0016] Among them, v x and v y is the residual of the image point coordinate, B is the geodetic longitude, L is the geodetic latitude, F and G are the functions in S2, and F0 and G0 are the approximate values ​​after substituting the current parameter values ​​into the function.

[0017] Furthermore, the virtual control point error equation is expressed as:

[0018]

[0019] Among them, v x and v y is the residual of the image point coordinate, and F0 and G0 are the approximate values ​​after substituting the current parameter values ​​into the function.

[0020] Furthermore, the expression of the normal equation is:

[0021]

[0022] Where t is the image space compensation function parameter, x is the object space coordinate correction, V is the error vector, and R is the constant vector.

[0023] A combined adjustment system for optical image and laser altimetry data includes a processor and a memory, wherein the processor calls a program in the memory to execute the following steps:

[0024] S1. Acquire image data to establish a strict optical image model, and convert the rectangular coordinates in the imaging model into geodetic coordinates;

[0025] S2. Add the system error affine model compensation to the imaging model, and use the flutter harmonic function in the compensation function to compensate for the low-order system error. The expression of the compensated imaging model is:

[0026]

[0027] Among them, v x and v y is the image point coordinate residual, x and y are the focal plane coordinates of the image point, f1 and f2 are the image compensation functions, a i 、ω i 、 a i’ 、ω i '、 is the vibration harmonic function parameter, b i 、c i and d i is the affine model parameter, n is the number of flutter harmonic functions;

[0028] S3. Introduce the connection point error equation, the elevation control point error equation and the virtual control point error equation to establish the normal equation, adopt the strategy of eliminating variables and modifying the normal equation to solve it, eliminate the object coordinate correction, construct a new modified normal equation and then perform adjustment calculation to obtain the system error compensation parameters.

[0029] Furthermore, the connection point error equation is expressed as:

[0030]

[0031] Among them, v x and v y is the image point coordinate residual, B is the geodetic longitude, L is the geodetic latitude, H is the distance from the ground point to the center of the reference ellipsoid, F and G are the functions in S2, and F0 and G0 are the approximate values ​​after substituting the current parameter values ​​into the function.

[0032] Furthermore, the error equation of the elevation control point is expressed as:

[0033]

[0034] Among them, v x and v yis the residual of the image point coordinate, B is the geodetic longitude, L is the geodetic latitude, F and G are the functions in S2, and F0 and G0 are the approximate values ​​after substituting the current parameter values ​​into the function.

[0035] Furthermore, the virtual control point error equation is expressed as:

[0036]

[0037] Among them, v x and v y is the residual of the image point coordinate, and F0 and G0 are the approximate values ​​after substituting the current parameter values ​​into the function.

[0038] Furthermore, the expression of the normal equation is:

[0039]

[0040] Where t is the image space compensation function parameter, x is the object space coordinate correction, V is the error vector, and R is the constant vector.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] This paper proposes a new method for jointly processing optical imagery and laser altimetry data that accounts for satellite platform flutter. This method considers flutter errors in the image model when establishing the error equation. An affine transformation model and a harmonic function are used to compensate for general systematic errors and periodic errors caused by flutter, respectively. Virtual control points are also used to address the rank deficiency of the normal equation coefficient matrix caused by the lack of plane control. This proposed joint adjustment method can effectively compensate for the effects of satellite platform flutter and improve the elevation positioning accuracy of images. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the process of the present invention.

[0044] Figure 2 This is the elevation error distribution map before adjustment for experimental verification. DETAILED DESCRIPTION

[0045] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0046] like Figure 1 As shown, this embodiment provides a method for joint adjustment of optical image and laser altimetry data, comprising the following steps:

[0047] Step S1: Acquire image data to establish a strict optical image model, and convert the rectangular coordinates in the imaging model into geodetic coordinates.

[0048] Step S2: adding system error affine model compensation to the imaging model, and using the dither harmonic function in the compensation function to compensate for low-order system errors.

[0049] Step S3, introduce the connection point error equation, the elevation control point error equation and the virtual control point error equation to establish the normal equation, adopt the strategy of eliminating the element to modify the normal equation to solve, eliminate the object coordinate correction, construct a new modified normal equation and then perform adjustment calculation to obtain the system error compensation parameter.

[0050] The details are as follows:

[0051] 1. Strict Imaging Model of Optical Imaging

[0052] High-resolution optical imaging typically uses a linear push-scan method to capture ground scenes. Different image lines have different projection centers and external orientations. A strict imaging model establishes a correspondence between object points and image points based on the camera's position and orientation at the moment of image formation. Every parameter in the imaging model has a strict physical meaning. The imaging model is based on the collinearity equation:

[0053]

[0054] Where X S 、Y S , Z S is the camera exterior orientation line element, a i 、b i 、c i are the elements of the exterior rotation matrix, f is the camera principal distance, and x0 and y0 are the focal plane coordinates of the principal point. The collinearity equation is based on the assumption that the projection center, image point, and object point are collinear at the instant of imaging. During image acquisition, it is not possible to record the exterior orientation elements for all rows. Generally, piecewise polynomial interpolation or directional slices are used to calculate the exterior orientation elements for each row.

[0055] Since the laser points used are used as elevation control, the rectangular coordinates X, Y, and Z must be converted into geodetic coordinates B, L, and H.

[0056]

[0057] Where B is the geodetic longitude, L is the geodetic latitude, and H is the distance from the ground point to the center of the reference ellipsoid.

[0058] 2. Joint Adjustment of Optical Imagery and Laser Altimetry Considering Satellite Flutter

[0059] For images affected by vibration, this embodiment adds a harmonic function model to the system error affine model compensation to further compensate for the vibration. The error equation is based on the collinearity equation and is specifically in the following form:

[0060]

[0061] Where, v x and v y is the image point coordinate residual, x and y are the focal plane coordinates of the image point, f1 and f2 are additional image compensation functions, where a i 、ω i 、 a i’ 、ω i '、 is the vibration harmonic function parameter, b i 、c i , and d i Affine model parameters, an affine transformation function is used in the compensation function to compensate for low-order system errors, and n harmonic functions (the value of n is determined according to the image deviation spectrum analysis results) are used to compensate for the periodic image deviation caused by chatter.

[0062] When establishing the adjustment model, considering that only elevation control without plane control in the model leads to unstable solutions and a tendency to rank deficiency, a small number of virtual control points are introduced in addition to elevation control points and tie points. Three types of error equations can be listed based on the point type.

[0063] (1) Connection point error equation:

[0064]

[0065] The plane coordinates and elevation values ​​of the image connection points are not accurate, so the three-dimensional coordinates in the error equation must be corrected.

[0066] (2) Error equation of elevation control point:

[0067]

[0068] The plane coordinates of the elevation control point are inaccurate, but the elevation value is accurate, so only the plane coordinates are corrected in the error equation, and the elevation value remains fixed.

[0069] (3) Virtual control point error equation:

[0070]

[0071] The virtual control point error equation assumes that the plane and elevation of the point remain unchanged; only the compensation parameters change. Because the virtual control points themselves contain all the errors in the imaging model, they are given a smaller weight when assigning weights to reduce their impact on the absolute accuracy after adjustment.

[0072] The three types of error equations are combined to obtain:

[0073] V=At+Bx-L;P (7)

[0074] Where t is the image space compensation function parameter, x is the object space coordinate correction, V is the error vector, L is the constant vector, A and B are the corresponding coefficient matrices, and P is the weight matrix. Construct the normal equation:

[0075]

[0076] When solving the problem, the strategy of eliminating variables and transforming the equation can be adopted to eliminate the object coordinate correction x, and then a new transformed equation can be constructed to calculate the system error compensation parameters by adjustment.

[0077] [A T PA-A T PB(B T PB) -1 B T PA]*t=A T PL-A T PB(B T PB) -1 B T PL (9)

[0078] 3. Experimental Verification

[0079] The experiment used a pair of HiRISE off-orbit stereo images of Mars, with high overlap and spatial resolutions of 0.25 meters and 0.5 meters, respectively. The laser point data used was MOLA data acquired by the Mars Global Surveyor satellite. Data labels were used to select laser points within the laser footprint that indicated flat terrain. These points were then back-projected onto the images and image matching was performed, resulting in 177 sets of laser elevation control points.

[0080] For off-track images, the left-right parallax is strongly correlated with the terrain. The MOLA laser elevation control points with the same name are intersected forward, and the calculated elevation is compared with the laser elevation. The error distribution is as follows: Figure 2 The elevation error in the figure shows periodic variations along the image rows, indicating the presence of periodic image chatter. Based on the proposed image square compensation method, 177 laser elevation control points were used in conjunction with the image. The elevation errors before and after adjustment are shown in Table 1.

[0081] Table 1 Mars HiRISE image and MOLA laser altimetry experiment results

[0082]

[0083] It can be seen that the elevation error before adjustment was 12.01 m, which was reduced to 3.7 m after adjustment. The image square deviation was also significantly reduced, indicating that for stereo images with vibration, the combined adjustment method proposed in this invention can effectively compensate for the impact of satellite platform vibration and improve the elevation positioning accuracy of the image.

[0084] In summary, this embodiment proposes a new method for jointly processing optical imagery and laser altimetry data that accounts for satellite platform flutter. This method considers the flutter errors present in the image model when establishing the error equation. An affine transformation model and a harmonic function are used to compensate for general systematic errors and periodic errors caused by flutter, respectively. Virtual control points are also used to address the rank deficiency of the normal equation coefficient matrix caused by the lack of plane control. The proposed joint adjustment method was validated using Mars HiRISE imagery and MOLA laser altimetry data. The results demonstrate that the proposed joint adjustment method can effectively compensate for the effects of satellite platform flutter and improve the elevation positioning accuracy of the image.

[0085] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A combined adjustment method of optical image and laser altimetry data, characterized in that: The following steps are involved: S1. Acquire image data to establish a strict optical image model, and convert the rectangular coordinates in the imaging model into geodetic coordinates; S2. Add the system error affine model compensation to the imaging model, and use the flutter harmonic function in the compensation function to compensate for the low-order system error. The expression of the compensated imaging model is: in, v x and v y is the image point coordinate residual, x and y are the focal plane coordinates of the image point, B is the geodetic longitude, L is the geodetic latitude, H is the distance from the ground point to the center of the reference ellipsoid, f 1 and f 2 is the image-side compensation function, a i 、 ω i 、 φ i 、 a i ’ 、 ω i '、 φ i ' is the vibration harmonic function parameter, b i 、 c i and d i are the affine model parameters, n is the number of flutter harmonic functions; S3. Introduce the connection point error equation, the elevation control point error equation and the virtual control point error equation to establish the normal equation, adopt the strategy of eliminating variables and modifying the normal equation to solve it, eliminate the object coordinate correction, construct a new modified normal equation and then perform adjustment calculation to obtain the system error compensation parameters.

2. a kind of optical image and laser altimetry data combined adjustment method according to claim 1, is characterized in that, The expression of the connection point error equation is: in, v x and v y is the image point coordinate residual, F, G is a function in S2, F 0 、 G 0 is the approximate value after substituting the current parameter value into the function.

3. a kind of optical image according to claim 1 and laser altimetry data combined adjustment method, it is characterized in that, The expression of the elevation control point error equation is: in, v x and v y is the image point coordinate residual, F, G is a function in S2, F 0 、 G 0 is the approximate value after substituting the current parameter value into the function.

4. a kind of optical image according to claim 1 and laser altimetry data combined adjustment method, it is characterized in that, The expression of the virtual control point error equation is: in, v x and v y is the image point coordinate residual, F 0 、 G 0 is the approximate value after substituting the current parameter value into the function.

5. a kind of optical image according to claim 1 and laser altimetry data combined adjustment method, it is characterized in that, The modified normal equation is: in, t is the image compensation function parameter, △ X is the object coordinate correction, R is a constant vector, A and B 1 is the coefficient matrix, P For the power array.

6. A combined adjustment system for optical image and laser altimetry data, characterized in that: The system comprises a processor and a memory, wherein the processor calls a program in the memory to execute the following steps: S1. Acquire image data to establish a strict optical image model, and convert the rectangular coordinates in the imaging model into geodetic coordinates; S2. Add the system error affine model compensation to the imaging model, and use the flutter harmonic function in the compensation function to compensate for the low-order system error. The expression of the compensated imaging model is: in, v x and v y is the image point coordinate residual, x and y are the focal plane coordinates of the image point, B is the geodetic longitude, L is the geodetic latitude, H is the distance from the ground point to the center of the reference ellipsoid, f 1 and f 2 is the image-side compensation function, a i 、 ω i 、 φ i 、 a i’ 、 ω i '、 φ i ' is the vibration harmonic function parameter, b i 、 c i and d i are the affine model parameters, n is the number of flutter harmonic functions; S3. Introduce the connection point error equation, the elevation control point error equation and the virtual control point error equation to establish the normal equation, adopt the strategy of eliminating variables and modifying the normal equation to solve it, eliminate the object coordinate correction, construct a new modified normal equation and then perform adjustment calculation to obtain the system error compensation parameters.

7. a kind of optical image and laser altimetry data combined adjustment system according to claim 6, is characterized in that, The expression of the connection point error equation is: in, v x and v y is the image point coordinate residual, F, G is a function in S2, F 0 、 G 0 is the approximate value after substituting the current parameter value into the function.

8. a kind of optical image and laser altimetry data joint adjustment system according to claim 6, is characterized in that, The expression of the elevation control point error equation is: in, v x and v y is the image point coordinate residual, B is the geodetic longitude, L is the geodetic latitude, F, G is a function in S2, F 0 、 G 0 is the approximate value after substituting the current parameter value into the function.

9. a kind of optical image and laser altimetry data joint adjustment system according to claim 6, is characterized in that, The expression of the virtual control point error equation is: in, v x and v y is the image point coordinate residual, F 0 、 G 0 is the approximate value after substituting the current parameter value into the function.

10. A combined adjustment system of optical image and laser altimetry data according to claim 6, characterized in that: The modified normal equation is: in, t is the image compensation function parameter, △ X is the object coordinate correction, R is a constant vector, A and B 1 is the coefficient matrix, P For the power array.

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