JPH0636497B2 - Reception environment evaluation method - Google Patents

Description

The present invention relates to a method for quantitatively evaluating a broadcast or mobile radio reception environment.

[Prior Art] Conventionally, examples of quantitatively expressing a reception environment include an occupied area ratio and an average floor number of buildings near an evaluation point. This is because the degree of crowding of buildings is related to the ease of receiving radio waves.

[Problems to be Solved by the Present Invention] It is not easy to acquire / update data of an occupied area ratio of a building and an average floor number used as a conventional quantitative expression of a receiving environment.

An object of the present invention is to quickly and easily quantitatively evaluate a receiving environment without using an active means such as electromagnetic radiation.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the reception environment evaluation method of the present invention is a method of projecting an image of a skyline scenery from an evaluation point onto a two-dimensional space by a camera to form an image of a feature and the sky. Skylines are detected using optical attributes such as differences in hue, saturation, and lightness, and the skyline angle, which is the elevation angle of the skyline in all directions with respect to the horizontal plane looking from the evaluation point, is a characteristic of the camera optical system. Using the optical axis, visual field, and image characteristic, the reception environment is quantitatively evaluated by the omnidirectional statistic, for example, the median value. Alternatively, the whole heavenly landscape is projected by a camera into a two-dimensional space and imaged,
The sky region is discriminated by using the difference in optical attribute between the feature and the sky, and the reception environment is quantitatively evaluated by the ratio of the sky region to the whole sky region. To implement them, a television camera is used as a line sensor or area sensor.

The characteristics of the camera optical system are obtained by shooting the skyline scenery from the evaluation point with a television camera equipped with a lens with a standard field of view, and using the difference in brightness, which is one of the optical attributes of the image, to obtain the skyline. To find the skyline angle. Skyline angles in all directions are obtained from a plurality of images covering all directions, and the reception environment is quantitatively evaluated by the median value, for example, as the omnidirectional statistic.

Since the scanning in the television standard system is horizontal, the scan data obtained by tilting the television camera by 90 degrees around the optical axis is obtained from the sky to the ground surface (or from the ground surface to the sky). When luminance is used as an optical attribute of an image, the high-luminance portion is regarded as a sky region, and the skyline angle is obtained based on the time for scanning the region and the total field-scanning time of the camera.

± 90 on camera lens in all directions with respect to optical axis
With a field of view and a fish-eye lens with an equiangular projection characteristic, the optical axis is aimed at the zenith, and an omnidirectional skyline landscape can be obtained in one image. Obtaining skyline coordinates in all directions from the brightness difference of the feature,
The skyline angle median value in all directions and the area ratio of the sky are obtained as the reception environment evaluation value. Further, the area ratio of the sky is obtained from the time required to scan the entire sky image and the integration time of the high brightness area scan in the entire sky image.

[Operation] According to the above method, the skyline landscape is converted into a two-dimensional image, the skyline is detected in the image,
The omnidirectional median of the skyline angle or the area ratio of the sky is measured, so that the reception environment can be quantitatively and easily evaluated.

The meaning of the skyline is the omnidirectional profile of the top of the farthest feature that can be seen from the evaluation point, which summarizes the shielding effect on the radio wave propagation of the feature in all directions seen from the evaluation point. Therefore, the omnidirectional median of the corners embodies the ability of the skyline to potentially evaluate the reception environment.

The skyline angle is equivalent to the diffraction angle of the radio wave when the evaluation point is the reception point and the transmission point is beyond the skyline where the direction is not specified.The larger the angle, the more the attenuation of the radio wave increases and the reception environment deteriorates. The omnidirectional center value of the skyline angle seen from the evaluation point is an amount suitable for expressing the reception environment of radio waves.

If the area ratio of the sky to the whole sky area is large, it is an open environment in which it is easy to receive radio waves, and if it is small, it is an environment in which it is difficult to receive because it is blocked by features, and it represents the reception environment like the skyline angle. .

By photographing the skyline landscape with a television camera, the boundary between the sky and the feature can be discriminated at high speed by an optical attribute such as a difference in brightness.

By attaching a fish-eye lens to the television camera, an all-sky skyline landscape image can be obtained with one image.

In the composite signal output from the television camera, by measuring the scanning time of the high output area corresponding to the high brightness part of the sky, the skyline angle omnidirectional center value or the sky area ratio can be measured at high speed.

[Example] An example will be described with reference to the drawings. First, a reception environment evaluation method by brightness processing of an image obtained by photographing with a television camera will be described.

In FIG. 1, a skyline landscape is photographed by a television camera 10 equipped with a lens 11 having a standard field of view, a clamp circuit 20 stabilizes a DC level, and a binarization circuit 30 binarizes a video signal portion. And records it in the frame memory 40. The optical attribute used to discriminate between the sky and the feature is that the brightness information is simple and a black and white camera can be used. In order to prevent the camera from being damaged by the sun, it is preferable to use an optical attenuation filter that attenuates the brightness and a CCD camera together.

The binarization circuit 30 binarizes the output of the clamp circuit 20 based on the difference between the brightness of each region of the sky and the feature. The clamp circuit 20 stabilizes the DC level, the binarization circuit 30 makes the rising and falling clear, and simplifies the data.

Since the brightness of the image differs depending on the weather / time or the material of the feature, it is desirable to adaptively change the brightness discrimination threshold accordingly. As a practical expedient, assuming that the camera output level corresponding to the brightness of the sky is 1, it is appropriate to set about 8% thereof as the threshold value. Alternatively, the clamp circuit 20
May be recorded in the frame memory 40, taken into the computer 50, and the skyline may be detected by differential filtering or the like.

In the binarized skyline landscape image shown in FIG. 2, the shaded portion 1 is the low-luminance region of the feature, the white portion 2 is the high-luminance region of the sky, and the boundary is the skyline 3 Is. The optical axis of the camera 10 is kept horizontal,
If the skyline landscape is isometrically projected in the captured image,
The visual field in the x-axis direction is ± φo degrees, the visual field in the y-axis direction is ± θo degrees, the x and y coordinates are φ and θ coordinates, and the skyline coordinates give the skyline angle θ at the azimuth angle φ as it is.

The camera orientation is changed to capture an omnidirectional skyline landscape, the skyline angle is obtained as described above, and the median value in all directions is used as the reception environment evaluation value. In this case, if the skyline angle is large, the shooting range may be exceeded, but in that case, it is advisable to additionally describe the field of view of the camera as the reception environment evaluation value. Alternatively, the elevation angle of the camera may be changed and the skyline scenery may be photographed to obtain the skyline angle as described above.
If the evaluation point is a high place, the skyline angle can be negative.

Although omnidirectional skyline landscape photography can be performed manually, it is convenient to perform remote photography by installing the camera 10 on a camera pedestal whose three-axis attitude is controlled by a magnetic azimuth sensor, a tilt angle sensor, and a servo mechanism.

Next, another method for evaluating the reception environment of the skyline image will be described.

When the camera 10 is tilted by 90 degrees around the optical axis to photograph the skyline landscape, the screen scanning is from top to bottom, for example. One of the composite signals from the television camera thus obtained
The line is shown in FIG. The horizontal sync pulse 81 rises to the high brightness part of the sky through the pedestal level 82, and the scanning advances to the low brightness part 84 of the feature to form the high brightness scanning area 83. The binarization circuit 30 binarizes the output of the clamp circuit 20 as shown in FIG. The time width τ is measured by the time width measuring device 60. The time width measuring device 60 has a threshold value of 8.
At 5, the time measurement starts with the [+] slope and ends with the [-] slope.

The scanning line number for each field is i, the vertical field of view of the camera is ± θo, and the horizontal field of view is ± φo, 1
If the effective scanning time of the line is τo (about 52 μs),
The skyline angle θ at the azimuth angle φ is approximately obtained by the following equation.

θ (φ) = θo · (τo−2τ) / τo (1) φ = φo · (i-131) / 131 (2) The median skyline angle for all directions is used as the reception environment evaluation value. This is the same as the evaluation by image processing.
The statistical processing is performed by transferring data from the time width measuring device 60 to the computer 50.

When shooting with a lens having a standard field of view, when the skyline angle increases, the skyline is restricted by the field of view of the camera lens, and the evaluation of the reception environment with the field of view of the camera added is complicated. This is a wide-angle lens, for example ±
It can be solved by using a 90 degree fisheye lens.

When the television camera 10 equipped with the fisheye lens 11 is aimed at the zenith and the whole sky is photographed, the whole sky image shown in FIG. 5 is obtained. The black part is the low brightness part 1 of the feature, and the white part is the high brightness part 2 of the sky. Assuming that the fisheye lens is an isometric projection, the circumference 90 of the circle to the center 0 is from an elevation angle of 0 degrees to 90 degrees.
The elevation angle coordinates are in concentric degrees, and the elevation angle coordinate θ (φ) of the high / low brightness boundary point 92 from the azimuth reference line 91 to the azimuth angle 93 (φ) is the skyline angle. In this case also, the median value of the skyline angles in all directions is used as the reception environment evaluation value. Alternatively, an average value may be used as the statistic.

The above was the reception environment evaluation by the skyline angle,
In the reception environment evaluation based on the area ratio of the sky, the area ratio of the high-brightness part to the whole sky area can be obtained from the whole sky image by the fisheye lens and used as the reception environment evaluation value.

A method for obtaining the area ratio of the sky by measuring the time when all-sky imaging with a fisheye lens is described. The field gate generation circuit 70, to which the output signal of the clamp circuit 20 is input, outputs the field gate signal during the effective field period (between the 22nd to 252nd horizontal scanning lines) excluding the vertical blanking period of each field. It is given to the time width measuring device 60. During this field gate, the time width measuring device 60
The high-luminance region time width of the output signal of the binarization circuit 30 is integrated. 1 frame from the line number effective line number excluding the number of lines in the vertical blanking interval N _0, the whole sky image is that falls between the first N ₁ line and the N ₂ line of one frame, the entire The time T required to scan the sky image area is approximately given by the following equation. For a rigorous discussion, we have to calculate if the whole sky image fits exactly between N ₁ and N ₂ , and otherwise, ie if there is an outer edge between scanlines. However, if the all-sky image is close to the state where the television screen is fully filled, the error is small even if the outer edge is rounded to the nearest scanning line, so the case of rounding will be described.

i: Operation line number in one field A = τ · (6/4) · (N ₂ −N ₁ ) / N ₀ (4) τ = 52 μs (effective scanning time for one line) (5) ξ = | sin ^-1 {(i−R) / R} | (6) R = (N ₂ −N ₁ ) / 2 (7) Suppose the high-intensity area scanning integration time of one field is S, an empty area for the whole sky image area. The rate J is given by the following equation.

J = S / T (8) [Advantages of the Invention] As described above, the present invention makes a two-dimensional image of a skyline landscape by camera shooting, and utilizes the difference between the optical attributes of the sky and the feature, such as brightness. Then, the skyline is obtained, and the reception environment is quantitatively evaluated by the median value which is the omnidirectional statistic of the skyline angle and the area ratio of the sky, so the electromagnetic environment is impaired without any means such as electromagnetic radiation. It is possible to easily evaluate the reception environment at the evaluation point without. In addition, evaluation can be speeded up by using a television camera as the camera. Binarizing an image speeds up signal processing and saves memory.

The skyline angle median value in all directions and the area ratio of the sky are also communicated.
It can be used for the field strength prediction calculation in the broadcast service area. For the electric field strength, for example, the prediction accuracy is improved by using a correction term according to the reception environment with the free space electric field strength as a reference value. In this case, for example, a polynomial is used as a function with the skyline angle omnidirectional median or the area ratio of the sky as a variable, and a polynomial coefficient that minimizes the squared error between the predicted value and the actual measurement result is obtained and the correction term is optimized.

By taking a picture with a television camera using a fish-eye lens, an all-sky skyline scene can be obtained with one image, and it is possible to save the calculation time of the omnidirectional median of all skyline angles and the area ratio of the sky, and the time and effort for camera operation.

The scanning time of standard television is about 16.7 per field.
Since it is ms, the receiving environment can be evaluated at high speed while traveling.

[Brief description of drawings]

FIG. 1 is a block diagram of the present invention, FIG. 2 is a skyline landscape image, FIG. 3 is one scanning line of a television composite signal, FIG. 4 is a binarization circuit output, and FIG. . 0 ... Coordinate origin, 1 ... Feature area, 2 ... Sky area, 3
...... Skyline. 10 ... Television camera, 11 ... Lens, 20 ...
... Clamp circuit, 30 ... Binarization circuit, 40 ... Frame memory, 50 ... Calculator, 60 ... Time width measuring instrument,
70 ... Field generation circuit. 81 ... Horizontal sync pulse, 82 ... Pedestal, 83 ...
… High brightness area, 84 …… Low brightness area. 90 ... circle with elevation angle of 0 degree, 91 ... azimuth reference line, 92
... skyline coordinates, 93 ... azimuth.

Claims (7)

[Claims] 1. In order to quantitatively evaluate a communication / broadcasting receiving environment, a skyline landscape including a feature and the sky viewed from an evaluation point is projected by a camera in a two-dimensional space to form an image. The skyline is detected using differences in optical attributes such as hue, saturation, and brightness of the sky, and the skyline angle, which is the elevation angle of the skyline in all directions with respect to the horizontal plane seen from the evaluation point, is the optical axis and field of view of the camera. A receiving environment evaluation method, wherein the receiving environment is evaluated using a median value, which is an omnidirectional statistic of the skyline angle, calculated using image characteristics. 2. The receiving environment evaluation method according to claim 1, wherein the skyline scenery is photographed by a television camera (10), and a clamp circuit (20) and a binarization circuit (3) are provided.
0) to record the image in the frame memory (40),
A reception environment evaluation method, characterized in that image data is loaded into a computer (50) and a skyline is detected with a high-luminance region as the sky. 3. The television composite obtained by the method for evaluating a reception environment according to claim 1, wherein the television camera (10) is tilted by 90 degrees around the optical axis to detect the skyline and the skyline landscape is photographed. A receiving environment evaluation method, characterized in that a scanning time width (83) of a high brightness area as an empty area in a signal is measured by a time width measuring device (60). 4. The receiving environment evaluation method according to claim 1, wherein the television camera (10) equipped with a fisheye lens (11) is photographed with the optical axis toward the zenith in order to obtain a skyline landscape image. Receiving environment evaluation method. 5. In order to quantitatively evaluate the communication / broadcasting reception environment, the whole sky view from the evaluation point is projected and imaged in a two-dimensional space, and the hue and saturation of the feature and sky, A reception environment evaluation method characterized by distinguishing sky regions using differences in optical attributes such as brightness and evaluating the reception environment by the ratio of sky regions to the whole sky region. 6. The reception environment evaluation method according to claim 5, wherein the whole sky is photographed by a television camera (10) equipped with a fisheye lens (11), and the frame memory (4) is recorded.
The whole sky image recorded in 0) is imported to the computer (50),
A reception environment evaluation method, characterized in that the area ratio of a high-luminance area to the entire area of an all-sky image is obtained and used as the area ratio of the sky. 7. The reception environment evaluation method according to claim 5, wherein the whole sky is photographed by a television camera (10) equipped with a fisheye lens (11), and the integration time is controlled by a field gate generation circuit (70). The time width measuring device (60) integrates the high-luminance region scanning time width of the output of the binarization circuit (30) for each field period, and the ratio (50) to the time required for scanning the whole sky image is calculated. A method for evaluating a reception environment, characterized in that the area ratio of the sky is obtained.