JP3201902B2 - Target angle measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a target angle measuring device for measuring the direction of a target using an image pickup device.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing a conventional target angle measuring device. In the figure, 1b is an optical system having no distortion, 2 is an imaging device, 3 is target detection means, 4b is angle calculation means B, and 5 is data output means.

Next, the operation will be described. Light incident on the optical system 1b having no distortion is imaged on an element of the imaging device 2 and output as an image. Here, the optical system having no distortion means that the angle θ formed by a target with respect to a certain reference axis shown in FIG. 2 and the image position (referred to as a reference point) of the reference axis shown in FIG. An optical system having a linear relationship with the distance r on the image. As the imaging sensor of the imaging device 2, a two-dimensional solid-state imaging device or a combination of an image intensifier and a two-dimensional solid-state imaging device is used. This is because these imaging sensors do not cause distortion by the sensors themselves. The above imaging device 2
The output image signal is subjected to processing (for example, binarization processing) for detecting only a high-luminance target in an image such as a missile flame by the target detection means 3. FIG. 4 shows the binarization process.
In the image obtained as described above, a luminance level equal to or higher than a certain luminance level (referred to as a threshold value) is set so that the relative luminance level is 1, and a luminance level equal to or lower than the threshold value is set to a relative luminance level. This is a process of converting the value to 0. With respect to the target obtained in this way, the direction of the target point from the reference point is calculated by the angle calculation means B4b. Since the angle calculation means B4b processes an image without distortion, the reference point is set to an arbitrary point on the image, and the horizontal and vertical directions of the target with respect to the reference point are determined by the distance on the image from this point to the target point. Is calculated. FIG. 3 shows the concept of the target and the reference point on the image as described above. In FIG. 3, when the target point is located at a distance (x, y) on the image with respect to the reference point, the target angles in the horizontal and vertical directions are (θx, θy) according to the following equations.

[0004]

(Equation 1)

Here, the target point is uniquely defined as a characteristic point such as the center of gravity or the brightest point of the target. The angle data thus obtained is displayed and output by the data output means 5.

[0006] Such a conventional target angle measuring device is constantly alert to threats such as missiles and aircraft,
Used to measure its direction of arrival.

[0007]

Since the conventional target angle measuring device is constructed as described above, when an optical system having distortion is used to convert a distance on an image into an angle, "Equation 1" is used. With a first-order conversion formula like this, an accurate target angle cannot be measured. This is because, in an optical system having distortion, a target angle and a distance on an image with respect to a certain reference point are non-linear, and are often rotationally symmetric. In general, the distortion of the optical system increases as the viewing angle increases. Therefore, according to the conventional method, an optical system having a wide viewing angle cannot be used. Therefore, in order to monitor a wide area with a conventional optical system having a narrow viewing angle, there is a method of mechanically moving the field of view of the apparatus within the range such as rotating the imaging apparatus itself to secure a wide field of view. Since the same visual field cannot be monitored, there is a problem that it is not possible to cope with an instantaneous phenomenon.

Further, in order to measure an accurate angle using an optical system having a wide viewing angle with distortion, the angle calculating means B4b requires data corresponding to an angle corresponding to each pixel of a two-dimensional image sensor. However, there is a problem that enormous data corresponding to all pixels is required, and enormous time and storage capacity of a huge processing device are required to measure the data. .

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide an apparatus capable of constantly monitoring a wide range and accurately measuring a target angle by using an optical system having distortion. And It is another object of the present invention to obtain an apparatus which can easily acquire data for the purpose and requires a small data storage capacity of the processing apparatus.

[0010]

SUMMARY OF THE INVENTION A target angle measuring apparatus according to the present invention measures an angle of a target using an optical system having rotationally symmetric distortion, so that an image on an image corresponding to the center of distortion of the optical system is measured. With the point as a reference point, the distance from the point to the target point on the image (r in FIG. 3) and the angle between the reference point and the horizontal line of the straight line connecting the target (φ in FIG. 3) are obtained from the image. Is to measure the angle.

[0011]

The target angle measuring device according to the present invention uses a center of distortion of an optical system as a reference axis and obtains a target angle based on the position of the target with respect to the reference axis. The advantage is that the target angle can be measured using an optical system having a wide viewing angle with aberration.

[0012]

【Example】

Embodiment 1 FIG. FIG. 1 is a configuration diagram showing one embodiment of the present invention. In the figure, 2, 3 and 5 are the same as those of the conventional apparatus. 1a is an optical system having rotationally symmetric distortion,
a is an angle calculating means A including a process of correcting distortion.

The angle calculating means A4a uses the center of distortion of the optical system in FIG. 3 as a reference point on the image, the distance r from the image to the target on the image, and the angle φ between the horizontal line connecting the reference point and the target point with the horizontal plane. Is obtained from the image to calculate the direction of the target.

First, a method of calculating the center of distortion of the optical system will be described. FIG. 5 is a configuration diagram at the time of acquiring data for calculating a distortion center. In FIG. 5, reference numerals 1a, 2 and 3 are the same as the configuration diagram of FIG. Reference numeral 6 denotes a distance calculating means for outputting and displaying the distance on the image in the horizontal and vertical directions from an arbitrary point to the target. Reference numeral 7 denotes a pseudo target, which is a light source for including the target in the acquired image. Reference numeral 8 denotes a rotary inclined table on which the mounting angle of the imaging device 2 can be freely set.

In order to calculate the distortion center, the origin is assumed near the center of the screen in the setting of FIG. 5, and the pseudo target is set at that point. The target position (x ', y') on the image is measured by adjusting the angle of the rotary table 8 so that the target moves in a constant angle step in the horizontal and vertical directions. Characteristics are obtained. When the horizontal or vertical angle is constant, (x ',
y ') is approximated by the method of least squares and the angle in the horizontal direction is fixed

[0016]

(Equation 2)

When the vertical angle is fixed

[0018]

(Equation 3)

The following approximate expression is obtained. Then, when the extremum of these equations is obtained, it becomes as shown by X in FIG. The extreme values calculated from “Equation 2” and “Equation 3” are each approximated by a linear expression as shown by a dashed line in FIG. 6, and the intersection point is set as the center of the distortion.

Next, a method of measuring the target angle will be described. In the configuration of FIG. 5, the light source 1a and the imaging device 2 are set such that the image of the light source is set on the image at the distortion center calculated as described above. The position of the target on the image is measured by moving the rotary tilt table 8 up, down, left, and right at fixed angle steps with respect to the distortion center. When the amount of change in the angle from the distortion center is the same in the vertical and horizontal directions, the distance on the image from the distortion center is compared, and it is confirmed that the measurement results in the four directions match. If they do not match, the above-described measurement is performed again by shifting the center of distortion by an amount corresponding to one or two pixels to search for the most matching point. Then, the relationship between the distance on the image and the angle from the distortion center obtained in this way is approximated by the least squares method or the like to obtain the following expression.

[0021]

(Equation 4)

In order to calculate the direction of the target using the target angle θ obtained as described above, the target angle is separated into horizontal (θaz) and vertical (θel). For this purpose, the following equation is used to calculate the angle φ between the distortion center on the image and the horizontal axis of the target point.

[0023]

(Equation 5)

[0024]

(Equation 6)

[0025]

As described above, according to the present invention, a target is extracted from an image captured using an optical system having a wide viewing angle having rotationally symmetric distortion, and the target is extracted from the image of the distortion center and the target. By calculating the direction of arrival of the target from the position, the angle of the target can be accurately measured by constantly monitoring a wide area.

Further, according to the present invention, when a conventional apparatus uses an optical system having distortion, one of the two-dimensional imaging elements can be used.
Compared with the method of providing data in which the angle is associated with each pixel, the time required for the measurement and the data required for the processing are reduced, so that the processing load on the angle calculating means is reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a diagram illustrating an angle between a reference axis of a wide-angle system and a target.

FIG. 3 is a diagram illustrating a concept of a target and a reference point on an image.

FIG. 4 is a diagram illustrating the concept of binarization processing.

FIG. 5 is a configuration diagram when a distortion center is calculated.

FIG. 6 is a diagram illustrating a method of calculating a distortion center.

FIG. 7 is a configuration diagram showing a conventional target angle measuring device.

[Explanation of symbols]

 1a Optical system with distortion 1b Optical system without distortion 2 Imaging device 3 Target detecting means 4a Angle calculating means A 4b Angle calculating means B 5 Data display processing 6 Distance calculating means 7 Pseudo target 8 Rotating tilt table

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-62-81180 (JP, A) JP-A-59-196665 (JP, A) JP-A-1-302474 (JP, A) JP-A-4- 278401 (JP, A) JP-A-2-206707 (JP, A) JP-A-5-48051 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01S 3/78-3 / 789

Claims (3)

(57) [Claims] 1. An optical system having rotationally symmetric distortion, an imaging device using a two-dimensional imaging sensor on which output light from the optical system is incident, and detecting only a target from an image signal obtained by the imaging device Target detection means, the distance between the distortion center of the optical system and the target on the image and on the image
The angle (φ) formed by the horizontal axis is detected and associated with the distance from the distortion center to the target point on the image calculated in advance .
Based on the relationship between the detected target angle and the detected distance.
The target angle (θ) is obtained, and the obtained target angle (θ) is obtained.
Angle calculation means for calculating a target direction from the detected angle (φ), and data output means for outputting angle data of the target direction calculated by the angle calculation means. A target angle measuring device characterized by the above-mentioned. 2. The angle calculation means calculates a center point of rotationally symmetric distortion of the optical system, and measures a relationship between a real angle of the target and a target position on an image using the distortion center as a reference point , Approximate the measurement result of this relationship by the least square method, etc.
Calculate the horizontal and vertical angles of the target from the distance on the image from the distortion center to the target and the angle on the image formed by the straight line connecting the distortion center and the target with respect to the horizontal line of the image using the approximate expression The target angle measuring device according to claim 1, wherein the target angle is measured. 3. A pseudo target is arranged in an arbitrary reference point direction on an image, and one of a horizontal direction and a vertical direction in an image pickup device is fixed, and the other direction is moved at a fixed angle step, and a horizontal direction is set. Measure the pseudo target position on each image in the fixed case and the fixed vertical direction , and measure
Approximation of specified pseudo target position by least square method
Equations are obtained, and the extremum of the obtained approximate expression is approximated to a linear expression in each of the case where the horizontal direction is constant and the case where the vertical direction is constant, and the intersection of the two approximate expressions is the center point of the rotationally symmetric distortion of the optical system. Is calculated, and the imaging device is moved at a fixed angle step from the calculated distortion center point, based on the movement angle, the target distance on the image from the distortion center point and the distance from the distortion center point direction at the distance. 2. The target angle measuring device according to claim 1, wherein a relationship with a target angle is obtained.