JPH0636189B2 - Image geometric distortion correction device - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention is to easily and effectively correct geometric distortion of image data of the ground surface, which is obtained by a scanner mounted on a flying object such as a satellite. The present invention relates to an apparatus for correcting geometric distortion of an image.

[Technical background of the invention and its problems]

Recently, it has been attempted to perform resource exploration using a surface image obtained by scanning the ground surface with a scanner mounted on a flying body such as an artificial satellite or an airplane. However, the above-mentioned image contains many geometrical distortions due to the attitude of the flying object, its flight trajectory, and the like. Therefore, in order to use the above image for resource exploration and the like, it is necessary to correct the geometrical distortion by using some means.

Therefore, conventionally, the geometric distortion of the image is corrected exclusively by statistical processing, but in recent years, for example, Japanese Patent Publication No. 59-1
Analytical geometric distortion correction as introduced in No. 0109 has also been attempted. This analytical geometric distortion correction uses the so-called annotation data such as the attitude of an artificial satellite or the like that obtains a ground surface image and its flight trajectory, and systematically performs the above-mentioned geometric correction at the Landsat receiving station or the like on the side that supplies the image. It is intended to correct the distortion. Therefore, the receiving station calculates the orbital information of the artificial satellite in the form of so-called six orbital elements, and according to this orbital information, the vector of the position and velocity of the artificial satellite is expressed as a function of time to correct the geometric distortion. ing.

However, in order to correct the geometric distortion of the image in this way, conversion processing from the attitude coordinate system of the artificial satellite to the image to its satellite orbit coordinate system, and further conversion from the satellite coordinate system to the earth center coordinate system However, there is a drawback that the processing is required, the processing process is complicated, and it takes too much time to perform the image processing.

Especially in the above conversion process, it is necessary to solve a non-linear orbital equation, which may cause a practical problem such as a case where it takes a long time for the solution to converge, a case where it diverges, and a case where there are multiple solutions. It was

[Object of the Invention]

The present invention has been made in consideration of such circumstances, and its purpose is to effectively use the geometric distortion of an image obtained from a flying object by effectively using the annotation data about the flying object. An object of the present invention is to provide a highly practical geometric distortion correction device for an image, which can be easily and highly accurately corrected by the user of the image.

[Outline of Invention]

The present invention basically corrects geometric distortion by using annotation data relating to a flying object for obtaining image data, and in particular, using the position data of the flying object included in this annotation data, The conversion function for converting the orbital coordinate system of the flying object to the earth center coordinate system is approximately obtained by data analysis, and the attitude of the flying object is corrected from the analysis of the point directly below the surface of the flying object. By converting the coordinate system for the image using the attitude information from the object coordinate system of the flying object to the trajectory coordinate system, and further converting the coordinate system of the image to the earth center coordinate system using the conversion function, The geometric distortion of an image is simply corrected with high accuracy.

〔The invention's effect〕

Thus, according to the present invention, the conversion function for converting from the orbital coordinate system to the earth center coordinate system is approximately obtained by data analysis while ensuring accuracy. Therefore, the conversion function can be solved by a non-linear equation. Unlike the one obtained by, there is no possibility that the solution will take a long time to converge, the solution will diverge, and there will be practically inconvenient points such as the case where there are multiple solutions. Also, the annotation data is corrected by analyzing the points directly below the surface of the flying object, and the corrected annotation data is used to convert the coordinate system of the image obtained by the flying object to the earth center coordinate system. The geometric distortion can be corrected very easily and effectively. That is, according to the present invention, compared with the statistical geometric distortion correction, the required number of ground standard points (GCP) is significantly reduced. For example, the conventional Landsat MS
In the case of S image processing, several tens of standard points were required, but at most 2-3 points are sufficient. Further, as compared with the conventional analytical geometric distortion correction, since the data attached to the image itself is directly used, less parameters need to be obtained.
Therefore, the image processing can be easily performed on the side of the user of the image, and the effect that the practical advantage thereof is great is exhibited.

Example of Invention

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention. The image data of the ground surface scanned and input by the scanner mounted on the flying object is input from the image data input unit 1.
On the other hand, from the attached information input unit 2, the annotation data such as the attitude and altitude of the flying object for which the image data is obtained, the position information of the point directly below the ground surface with respect to the center position of the image, and the like are input, and the control unit 3 is input. Has been given. Control unit 3
As will be described later, the geometrical distortion amount for the image data is calculated according to these information, and the calculation result is given to the distortion correction calculation circuit 4.

The distortion correction calculation circuit 4 corrects and outputs the geometric distortion of the image data input through the image data input unit 1 according to the geometric distortion amount thus obtained. , For example, as shown in FIG. The image data whose distortion has been corrected by the distortion correction calculation circuit 4 is output via the image output unit 5. Therefore, the distortion correction calculation circuit 2 is, for example, as shown in FIG.
a, a coordinate calculation circuit 4b, an image register 4c and the like. Then, the position coordinates (i, j) of the image data obtained by the scanner of the flying object are set to the respective coordinate calculation circuits 4a,
4b, and the geometrical distortion corrected coordinates (X, Y) of the image are calculated according to the image distortion amount. Image register
4c is the above position coordinates until this coordinate calculation is completed.
The image data of (i, j) is once stored, and the image data is output together with the converted coordinate data (X, Y).

FIG. 3 shows the concept of correction processing of geometric distortion of an image in this apparatus. This geometric distortion correction process is basically based on the image data, annotation data, position data of the image center on the ground surface, etc., which are input from the data input unit, and the earth center coordinates (geodetic coordinates) corresponding to the image. ) Is calculated (geodetic coordinate calculation unit). Then, according to the calculation result, projected coordinate conversion to the earth center coordinate system for the input image is performed (projection coordinate calculation unit), and the image data obtained by the earth center coordinate system is obtained.
It is configured so as to obtain the image whose geometric distortion has been corrected.
FIG. 4 shows a specific example of the configuration of the processing circuit. The geometrical distortion correction of an image in this apparatus will be described in detail with reference to FIG.

Define scanner coordinates to describe the behavior of the scanner. As shown in FIG. 5, the flight direction of the flying object is set to the _xs axis,
The scanning direction and y _s axis, determine the z _s axis as right-handed orthogonal coordinate system with the x _s-axis and y _s axis. The z _s axis is usually the normal direction down from the projectile to the surface of the earth.

Now, it is assumed that the pixel coordinates of the image 30 of the ground surface obtained by the scanner mounted on the flying object are represented by (i, j). In this case, the direction ds (i, j) in which the scanner that obtains the image looks into the earth's surface (earth), the estimated angle with respect to the pixel (ij) of the target on the image is θi, ψj, Given in. The view angle calculation circuit 11 in FIG. 4 calculates the angles θi, ψj according to the coordinate data (i, j) of the image indicated by the counter 12, and the direction cosine calculation circuit 13 calculates the angle view angles θi, ψj from the angle view angles θi, ψj. Seeking vector ▲ ▼. Then, this vector ▲ ▼ (i, j) can be expressed in its trajectory coordinate system by using the three-axis rotation angles (α, β, γ) of the flying object. Here, the trajectory coordinate system of the flying object and the three-axis rotation angles (α, β, γ) of the flying object.
Is as shown in FIG. That is, the orbit coordinate system has the position of the flying object as the center and the trajectory direction of the flying object is x.
_{The 0} axis, the direction perpendicular to the orbital plane is the y ₀ axis, and the earth center direction is z
It is defined as a right-handed orthogonal coordinate system with ₀ axis. Also, x
The rotation angle around the ₀ axis is α, the rotation angle around the y ₀ axis is β,
Let γ be the rotation angle around the z ₀ axis.

On the other hand, the correction amount of the attitude angle of the flying object with respect to the image is calculated from the difference between the point directly below the image center and the ground standard point (Δα,
Δβ, Δγ). Therefore, the time at which the flying object obtains an image is set to t = t (i, j), and the correction amount of the attitude angle of the flying object at the time t is approximated by a third-order polynomial. Letting the correction amount related to the attitude of the flying object be α (t), β (t), γ (t), the correction amount is α (t) = α ₀ + α ₁ t + α ₂ t ² + α ₃ t ³ + Δα β (t) = β ₀ + β ₁ t + β ₂ t ² + β ₃ t ³ + Δβ γ (t) = γ ₀ + γ ₁ t + γ ₂ t ² + γ ₃ t ³ + Δγ. By using such a correction amount, the relationship between the trajectory coordinate system of the flying object and the coordinate system of the scanner that obtained the image is converted into a conversion function T ^s ₀ Can be asked as Where the above conversion function ▲ ^s ₀ ▼
Is ▲ T ⁰ _s ▼ = (▲ T ^s ₀ ▼) ^t . By using this ▲ T ⁰ _s ▼, the vector ▲ ▼ in the coordinate system of the scanner is Is converted to the orbit coordinate system. The tables 14 and 15 shown in FIG. 4 are based on the time information t (i, j) obtained by the time calculation circuit 16 and the above-described posture correction amounts (α, β, γ, Δα, Δβ,
Δγ), and the calculation circuit 17 calculates the relationship (conversion function) between the coordinate systems according to these information.
Seeking T ⁰ _s ▼. The calculation circuit 18 performs the above-mentioned coordinate system conversion in accordance with this conversion function {circumflex over (T ⁰ _s) }.

On the other hand, the relationship ∇T ⁰ _g ▼ between the orbit coordinate system in which the orbit information is first-order approximated and the central coordinate system of the earth is given by the following function. That is, the latitude on the earth at the point directly below the center of the image is represented by λn = λn (t) = λ0 + λ1 × t ψn = ψn (t) = ψ0 + ψ1 × t, and its altitude is similarly hn = hn (t ) = H0 + h1 × t, the conversion function ▲ T ⁰ _g ▼ is
Captured as an image rotation of a composite angle i'of the angle i formed by the above-mentioned latitude and longitude at the image center and the rotation angle of the earth when the flying object rotates by longitude λ and latitude ψ as the azimuth angle. To be This rotation angle is approximately obtained by data analysis, where i ′ is i ′ = tan ⁻¹ {(∂ψn / ∂t) ÷ (∂λn / ∂t)}.

Therefore, the conversion function ▲ T ⁰ _g ▼ is It is represented by. However, the conversion function ▲ T ⁰ _g ▼ is ▲ ^g ₀ ▼ = (▲ T ⁰ _g ▼) ^t . By using this conversion function ▲ ^g ₀ ▼, it becomes possible to convert the vector of the orbit coordinate system to the earth center coordinate system. Here, the earth center coordinate system is as shown in FIG. That is, with the center O of the earth as the origin,
It is defined as a right-handed orthogonal coordinate system with the north polar axis as the z _i axis and the vernal equinox direction as the x _i axis. Also, the position Q of the flying object at this time
The x ₀ axis, the y ₀ axis z, and the ₀ axis in the orbital coordinate system centered at are also shown at the same time. The calculation circuits 19 and 20 shown in FIG. 4 are the latitude and longitude θn, ψ of the point directly below the image.
n and the rotation angle i ′ are respectively obtained, and the calculation circuit 21 calculates the conversion function ∑T ^g ₀ ▼ from these calculation results. Then, the trajectory vector Is the radius of the earth r = r (ψn (t)) Is required as. this By applying the conversion function ▲ T ^g ₀ ▼ to the calculation circuit 22 or the like, Is calculated. As a result, the direction vector calculation circuit 23 The earth center coordinate vector is calculated. Then, from this direction vector, the position coordinate indicated by the geometric distortion-corrected earth center coordinate of the image, that is, the latitude / longitude coordinate of the center position of the image is ψ = sin ⁻¹ a ₃ λ = ATAN2 (a ₂ / cos ψ, It is obtained by the geodetic coordinate calculation circuit 24 as a ₁ / cos ψ).
Here, the latter one of the above two equations for obtaining λ is
It is a function of two variables defined in JIS FORTRAN.

Then, the correction of the geometric distortion of the image of interest here is to correct the morphological distortion of the image, in other words, the image obtained from the projectile is made similar to the terrain. Means that. Therefore, if an image conversion process of g × f; (i, j) → (u, v) is performed using the above-mentioned correspondence f between coordinate systems and the map projection function g corresponding to the image, It is possible to effectively obtain a projected image without geometric distortion.

As described above, according to the present invention, after the coordinate system of the image obtained from the scanner mounted on the flying object is converted into the trajectory coordinate system of the flying object by using the annotation data, the point directly below the image is on the ground surface. The rotation angle i ′ is obtained from the latitude and longitude information λn, ψn of the image and the geometrical distortion of the image is corrected by converting the orbital coordinate system to the earth center coordinate system according to the rotational angle i ′. Is very easy. That is, using the coordinate system conversion functions ▲ T ⁰ _s ▼ and ▲ T ^{g 0} ▼, the direction vector ▲ ▼ and the trajectory vector Is converted to the earth center coordinate system, and the direction vector ag that looks at the target point from the earth center is ▲ ▼ ＝ ▲ ▼ (r, ▲ ▼, ▲ ▼) ＝ (a
₁ , a ₂ , a ₃ ), and according to this direction vector ▲ ▼, the latitude and longitude (λ, ψ) of the target point are ψ = sin ⁻¹ a ₃ λ = tan ⁻¹ ₂ (a ₂ / cos ψ, a ₁ / Cosψ) can be obtained easily and accurately. In this way, the geometrical distortion of the image obtained by the flying object can be effectively corrected, and the image can be widely used for exploration of resources on the ground surface, for example.

The present invention is not limited to the above embodiment. For example, in the embodiment, λn (t) and ψn (t) are set to 1 of t.
Although the approximation is performed using a quadratic function, the approximation may be performed using a quadratic function, a cubic function, or a cubic function or higher. By doing so, it is possible to perform image processing with higher accuracy. In this case, if considered locally, the first-order approximation is made at the point directly below each local, so it is sufficient to perform the above-mentioned approximation at each local. In short, the present invention can be variously modified and implemented without departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of an apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing a configuration example of a distortion correction calculation circuit, and FIG. 3 is a geometric distortion correction processing according to the present invention. FIG. 4 is a diagram showing a schematic flow of FIG. 4, FIG. 4 is a diagram showing a specific example of the geometric distortion process, and FIGS. 5 to 7 are diagrams for explaining the process in the present embodiment. 1 ... Image data input section, 2 ... Attached information input section, 3 ...
... control section, 4 ... distortion correction calculation circuit, 5 ... image output section,
11 …… Estimation angle calculation circuit, 13 …… Direction cosine calculation circuit, 14
…… Posture table, 15 …… Correction amount table, 17 …… ▲ T
⁰ _s ▼ Calculation circuit, 19 …… Direction point longitude / latitude calculation circuit, 20 …… Rotation angle calculation circuit, 21 …… ▲ T ^{g 0} ▼ Calculation circuit, 23 …… Direction vegetation calculation circuit, 14 …… Geodesic coordinate calculation circuit .

Claims (1)

[Claims] 1. A means for inputting image data obtained by scanning a ground surface from a flying object, and annotation data including information on a posture of the flying object and a position on the ground surface immediately below when the image data is collected. Means to enter
A means for approximately obtaining a conversion function for converting the trajectory coordinate system of the flying object to the earth center coordinate system using the information on the position of the flying object, and the ground surface corresponding to a specific pixel in the input image data. Means for obtaining the position coordinate data of the position data using the annotation data, the position coordinate data obtained by this means, and the reference position coordinate data on the ground surface obtained in advance for the specific pixel Means for correcting the information on the attitude of the flying object in the annotation data, and the position of each pixel of the input image data on the ground surface using the annotation data including the corrected information on the attitude of the flying object and the conversion function A geometric distortion correction device for pixels, comprising: means for obtaining coordinate data.