CN112258406B - Linear array push-broom CCD image rapid automatic geometric correction method - Google Patents
Linear array push-broom CCD image rapid automatic geometric correction method Download PDFInfo
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Abstract
A method for quickly and automatically correcting a linear array push-broom CCD image belongs to the technical field of image processing. The invention aims to provide a rapid automatic geometric correction method for a linear array push-broom CCD image, which is correctable only by basic parameters such as a camera focal length, a field angle, a mounting angle, a flying height and the like without depending on camera position and attitude parameters obtained by a sensor. The invention relates to a method for quickly and automatically correcting the geometry of an object image of a linear array push-broom CCD image at a certain moment, wherein AB represents a linear array push-broom CCD image line at the moment, and AB represents a line in a corresponding object plane. The invention can realize rapid and automatic geometric correction without manually selecting control point pairs, and the corrected image can meet the requirements of interpretation and mosaic.
Description
Technical Field
The invention belongs to the technical field of image processing.
Background
As shown in fig. 1, the linear array push-broom type CCD camera is installed on the flying platform, and images are formed one line at each moment, and the camera is pushed forward to complete the whole image as the platform flies forward. In practical application, three parallel installation modes are often adopted to expand the field angle and the imaging range, as shown in fig. 2, three linear array CCD cameras are placed along the flight direction in the order of right inclination, vertical inclination and left inclination, the middle CCD camera has two linear array CCD photosensitive elements to generate two strips, in order to avoid the omission of the target in the imaging, the two linear array CCD photosensitive elements are partially overlapped, the left and right cameras are provided with certain installation angles to image the ground target, and each linear array CCD photosensitive element is provided with one photosensitive element to generate one strip. Because the left camera and the right camera are provided with certain installation angles, the left camera and the right camera are actually oblique imaging and need to be corrected. The scale of the oblique image along the oblique direction is not uniform, the scale is gradually reduced from a close shot line to a far shot line, the oblique imaging image and the vertical imaging image cannot be directly embedded due to the existence of parallax, and the geometric correction of the linear array push-broom CCD image is to correct the oblique imaging image into an orthoimage so that the orthoimage can be embedded and spliced with the middle vertical imaging camera image.
Typical geometric correction methods include strict geometric correction and approximate geometric correction, both of which have limitations that do not meet practical needs in some cases. The strict geometric correction needs to obtain six accurate external orientation elements of the camera to accurately calculate the parameters of the correction formula and obtain a good correction result, and if the position and posture sensors on the camera cannot achieve the parameters, the use of the strict geometric correction is influenced. The parameters of the approximate geometric correction formula are calculated by manually selecting enough control point pairs, the correction efficiency is low because of manual operation, the use is limited under the condition of strict requirements on the correction time, and automatic correction cannot be realized.
Disclosure of Invention
The invention aims to provide a rapid automatic geometric correction method for a linear array push-broom CCD image, which is correctable only by basic parameters such as a camera focal length, a field angle, a mounting angle, a flying height and the like without depending on camera position and attitude parameters obtained by a sensor.
The invention relates to a geometric relation of imaging instant object images of a linear array push-broom CCD image at a certain moment, wherein AB represents a linear array push-broom CCD image line at the moment, AB represents a line in a corresponding object plane, the object image relation is established based on a geometric relation method, a mathematical model of a rapid automatic geometric correction method of the linear array push-broom CCD image is obtained, namely a coordinate transformation relation between an original image to be corrected and an image after correction is obtained, and geometric correction is carried out on the original image based on the mathematical model to obtain a corrected image; wherein: s is a projection center, O is a principal point, O' is a projection point of the principal point on an orthoscopic image, SO represents a principal optical axis of the oblique camera, the length is a focal length f of the camera, AB represents an oblique image surface, AB represents an orthoscopic image surface, SN represents a flight height, H represents, SP represents a shooting height of the oblique camera, M represents 0 Representing ground object points, M representing M 0 At the projection point of the oblique image,M represents M 0 In the projection point of the orthographic image, alpha is an included angle between a main optical axis of the camera and a ground vertical line, namely a camera inclination angle, beta is an included angle between SA and a main optical axis SO, namely a half field angle of the inclined camera, and omega is an included angle between AS and MS;
step one, the corresponding relation of the corrected image points and the original image points in the inclined direction, namely the corresponding relation of the abscissa:
let X = AM,
in Δ ASO, there are
AO＝SO·tanβ＝ftanβ
In Δ SOM, there are
OM＝SO·tan(ω-β)＝f·tan(ω-β)
Then
In Δ Snm, there are
nm＝Sn·tan(α-β+ω)＝ftan(α-β+ω)
In Δ Sna, there are
na＝Sn·tan(α-β)＝ftan(α-β)
Substituting the formula (1) into the formula (2) and simplifying the formula:
the above expression (3) expresses the corresponding relationship between the corrected image point and the original image point in the oblique direction, and the inverse image gray interpolation transformation formula is as follows:
the formula (4) is an expression of the mathematical model of the geometric correction method in the inclined direction;
step two, the corresponding relation of the corrected image points and the original image points in the flight direction, namely the corresponding relation of the vertical coordinates:
the relationship that the height of an ortho image corresponds to the flying height SN, the photographing height of an oblique camera corresponds to the distance from the photographing center to the ground along the main optical axis, and the image is represented as SP can be obtained
Y＝ycosα (5)
Wherein ν represents the flying speed;
expression (5) is an expression of the mathematical model of the geometric correction method in the flight direction.
The invention can realize rapid and automatic geometric correction without manually selecting control point pairs, is suitable for scenes that geometric correction can not be carried out when the position and the attitude parameters of the camera cannot be accurately obtained or the manual control point pair selection cannot be carried out, and the corrected image can meet the requirements of interpretation and mosaic.
Drawings
FIG. 1 is a linear array push-broom CCD camera imaging mode;
FIG. 2 is a schematic diagram of a linear array push-broom CCD camera mounted in three parallel;
FIG. 3 is a geometric relationship of object images at the moment of linear array push-broom CCD image imaging;
FIG. 4 is a geometrical relationship of the middle and low altitude CCD camera image imaging instant;
FIG. 5 is a geometrical relationship of the middle and low altitude CCD camera image imaging instant;
FIG. 6 is an original image of three parallel cameras; wherein (a) is a left tilt camera original image; (b) is the right tilt camera original image;
FIG. 7 is a correction result image of the present invention; wherein (a) is a left tilt camera original image; and (b) is a right tilt camera original image.
Detailed Description
Mathematical model formula derivation of linear array push-broom CCD image rapid automatic geometric correction method
Basic principle of the correction method
If the linear array push-broom CCD camera is obliquely installed, the scale of an oblique image along the oblique direction is not uniform, deformation is generated, and the position relation of a real ground object cannot be reflected. The linear array push-broom CCD camera images one line at a time, and the correction of the entire image can be accomplished by correcting each line of the entire image from the push-broom start point to the push-broom end point as shown in fig. 1, respectively. The geometric relation of an imaging instant object image of a linear array push-broom CCD image at a certain moment is shown in FIG. 3, AB represents a linear array push-broom CCD image line at the moment, and AB represents a line in a corresponding object plane.
Wherein: s is a projection center, O is a principal point, O' is a projection point of the principal point on an orthoscopic image, SO represents a principal optical axis of the oblique camera, the length is a focal length f of the camera, AB represents an oblique image surface, AB represents an orthoscopic image surface, SN represents a flight height, H represents, SP represents a shooting height of the oblique camera, M represents 0 Representing ground object points, M representing M 0 At the projection point of the oblique image, M represents M 0 At the projection point of the orthographic image, alpha is an included angle between a main optical axis of the camera and a ground vertical line, namely a camera inclination angle, beta is an included angle between SA and a main optical axis SO, namely a half field angle of the inclined camera, and omega is an included angle between AS and MS.
The first step, the corresponding relation of the corrected image point and the original image point in the inclined direction (abscissa) is set as X = AM, X = AM,
in Δ ASO, there are
AO＝SO·tanβ＝ftanβ
In Δ SOM, there are
OM＝SO·tan(ω-β)＝f·tan(ω-β)
Then
In Δ Snm, there are
nm＝Sn·tan(α-β+ω)＝ftan(α-β+ω)
In Δ Sna, there are
na＝Sn·tan(α-β)＝ftan(α-β)
Substituting the formula (1) into the formula (2) and simplifying the formula:
the above expression (3) expresses the corresponding relationship between the corrected image point and the original image point in the oblique direction, and the inverse transformation formula of the image gray level interpolation is as follows:
equation (4) is an expression of the mathematical model of the geometric correction method in the oblique direction.
And step two, acquiring the relationship between the corrected image point and the original image point in the flight direction (vertical coordinate) and the relationship between the vertical coordinate Y of the corrected image and the vertical coordinate Y of the original image through scanning speed, wherein the linear array CCD image is push-broom imaging, the scanning speed is in direct proportion to the speed-height ratio, and the vertical coordinate of the image is in inverse proportion to the scanning speed.
The relationship that the height of an ortho image corresponds to the flying height SN, the photographing height of an oblique camera corresponds to the distance from the photographing center to the ground along the main optical axis, and the image is represented as SP can be obtained
Y＝ycosα (5)
Wherein ν represents the flying speed;
expression (5) is an expression of the mathematical model of the geometric correction method in the flight direction.
Integrity verification of the present invention
The derivation above is that the M point is taken from the BO segment, and to verify the generality of the formula, it is verified whether the formula expression holds for the position of the M point under different conditions, as shown in FIG. 4, and the image point M is selected in the AO segment 1 ，m 1 To correct the image plane corresponding image point.
am 1 ＝nm 1 -na＝ftan(α-β+ω)-ftan(α-β)＝am
Therefore, the correction formula holds and the expression agrees whether in the AO section or the BO section.
When the original image plane intersects the corrected image plane, as shown in FIG. 5, at an arbitrary point M in the AC segment 2 ，M 2 The image point on the corrected image surface is m 2 Arbitrarily take a point M at the CB section 3 ，M 3 The image point on the corrected image surface is m 3 。
AM 2 ＝AO-OM 2 ＝ftanβ-ftan(β-ω)＝AM
am 2 ＝nm 2 -na＝ftan(α-β+ω)-ftan(α-β)＝am
AM 3 ＝AO+OM 3 ＝ftanβ+ftan(ω-β)＝AM
am 3 ＝nm 3 -na＝ftan(α-β+ω)-ftan(α-β)＝am
Therefore, when the original image plane and the corrected image plane intersect, the correction formula is established and the expressions match.
In summary, the geometric correction mathematical model is true and the expressions are consistent for any image point on the original image surface no matter whether the image surfaces before and after correction intersect.
Image geometry correction procedure and result analysis
1. Step of geometric correction
Firstly, obtaining an original image to be corrected of a three-parallel linear array push-broom CCD camera according to the mode of the linear array push-broom CCD image imaging principle;
secondly, according to the process of mathematical model formula derivation, the object-image relationship is obtained based on basic parameters such as the focal length, the field angle, the installation angle and the like of the camera, wherein the object-image relationship comprises the formulas (4) and (5);
thirdly, calculating the image frame range of the corrected image by using the formulas (4) and (5);
and fourthly, performing pixel resampling by adopting a bilinear interpolation method by using formulas (4) and (5) to obtain a corrected image.
Corrected result
Fig. 6 is an image obtained by the linear array push-broom CCD camera in a three-parallel mounting manner, two images being respectively images taken by the left oblique camera and the right oblique camera, and fig. 7 is an image corrected by the method.
Analysis of correction results
The correction result of the method is shown in fig. 7, compared with the original image in fig. 6, the image is stretched from the distant view (left side) to the near view (right side), the stretching effect is gradually reduced, the consistency of the scale is kept in the vertical direction, the image is not greatly changed in shape, and the method also provides favorable conditions for subsequent strip inner splicing. Due to the continuity advantage of the linear array push-broom camera, splicing in the strips can be directly aligned and spliced, and the consistency of the scale in the vertical direction reduces the workload and the accumulated error of subsequent splicing tasks.
Claims (1)
1. A method for quickly and automatically correcting the geometry of a linear array push-broom CCD image is characterized by comprising the following steps: the method comprises the steps that a linear array push-broom CCD image is subjected to imaging at a certain moment, an object image geometrical relationship is formed, AB represents a linear array push-broom CCD image line at the moment, AB represents a line in a corresponding object plane, the object image relationship is established based on a geometrical relationship method, a mathematical model of the linear array push-broom CCD image rapid automatic geometrical correction method is obtained, namely a coordinate transformation relationship between an original image to be corrected and an image after correction is obtained, and the original image is subjected to geometrical correction based on the mathematical model to obtain a corrected image; wherein: s is a projection center, O is a principal point, O' is a projection point of the principal point on an orthoscopic image, SO represents a principal optical axis of the oblique camera, the length is a focal length f of the camera, AB represents an oblique image surface, AB represents an orthoscopic image surface, SN represents a flight height, H represents, SP represents a shooting height of the oblique camera, M represents 0 Representing ground object points, M representing M 0 At the projection point of the oblique image, M represents M 0 In the projection point of the orthographic image, alpha is an included angle between a main optical axis of the camera and a ground vertical line, namely a camera inclination angle, beta is an included angle between SA and a main optical axis SO, namely a half field angle of the inclined camera, and omega is an included angle between AS and MS;
step one, the corresponding relation of the corrected image points and the original image points in the inclined direction, namely the corresponding relation of the abscissa:
let X = AM,
in Δ ASO, there are
AO＝SO·tanβ＝f tanβ
In Δ SOM, there are
OM＝SO·tan(ω-β)＝f·tan(ω-β)
Then
In Δ Snm, there are
nm＝Sn·tan(α-β+ω)＝f tan(α-β+ω)
In Δ Sna, there are
na＝Sn·tan(α-β)＝f tan(α-β)
Substituting the formula (1) into the formula (2) and simplifying the formula:
the above expression (3) expresses the corresponding relationship between the corrected image point and the original image point in the oblique direction, and the inverse image gray interpolation transformation formula is as follows:
the formula (4) is an expression of the mathematical model of the geometric correction method in the inclined direction;
step two, the corresponding relation of the corrected image points and the original image points in the flight direction, namely the corresponding relation of the vertical coordinates:
for an orthographic image, the altitude corresponds to the flying altitude SN, for a tilted camera, the shooting altitude corresponds to the distance from the shooting center to the ground along the main optical axis, represented as SP on the image, the relationship can be obtained
Y＝y cosα (5)
Wherein ν represents the flying speed;
expression (5) is an expression of the mathematical model of the geometric correction method in the flight direction.
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| CN103345761A (en) * | 2013-07-30 | 2013-10-09 | 中国地质大学（武汉） | Method and system for correcting and jointing tilted scanning and imaging data of linear array tower |
| CN105931200A (en) * | 2015-12-01 | 2016-09-07 | 中国科学院上海技术物理研究所 | Quick geometric precise correction method for small area array spaceborne TDI CCD camera |
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| CN103345761A (en) * | 2013-07-30 | 2013-10-09 | 中国地质大学（武汉） | Method and system for correcting and jointing tilted scanning and imaging data of linear array tower |
| CN105931200A (en) * | 2015-12-01 | 2016-09-07 | 中国科学院上海技术物理研究所 | Quick geometric precise correction method for small area array spaceborne TDI CCD camera |
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| 面阵CCD航空相机斜视图像几何畸变校正误差分析;周前飞等;《仪器仪表学报》;20140615;全文 * |
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