KR101631307B1 - Vehicle Detector Using Geo Magnetic Sensor and Detecting Method thereof - Google Patents

Abstract

A vehicle sensing apparatus using a geomagnetic sensor and a sensing method thereof are disclosed. The vehicle sensing apparatus of the present invention recognizes a vehicle by sensing a change in a geomagnetic field caused by a vehicle passing through a vehicle passage. At this time, the vehicle sensing apparatus can calculate the number of passed vehicles accurately even when the change of the earth magnetic field is not classified according to the vehicle as the vehicle continuously passes by using the distance sensor separately.

Description

TECHNICAL FIELD [0001] The present invention relates to a vehicle detection device using a geomagnetic sensor,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to a vehicle sensing apparatus using a geomagnetic sensor, and more particularly, to a vehicle sensing apparatus that corrects sensing errors of a geomagnetic sensor using a distance sensor and a sensing method thereof.

A geomagnetic sensor or a geomagnetic sensor is a sensor that detects a change in a geomagnetic field by using a magnetoresistive element whose resistance value changes according to a change of a magnetic field. Anisotropic magnetic resistance (AMR), giant magnetic resistance (GMR), and the like are usually applied to the magnetoresistive element used in the geomagnetic sensor.

The AMR or GMR devices currently available on the market also use special devices whose resistance values change with the intensity of the magnetic field. When the magnetic field is physically measured, the resistance of the internal device depending on the direction of the sensor and the direction of the magnetic field Change.

The AMR device is a magnetoresistive material with isotropic properties of nickel and iron. It is made of a thin and long film, and its resistance value changes according to the magnetic momentum generated when an external magnetic field is applied.

On the other hand, the earth's magnetic field distributed on the surface of the earth is always present at an average magnetic flux density of about 0.5 Gauss, although there is a slight difference according to latitude. The distribution of the earth's magnetic field can be changed by a ferro-magnetic material such as iron or an iron alloy. The ferromagnetic material has a density of the earth's magnetic field up to a certain range (hereinafter simply referred to as a " It brings change. When a ferromagnetic material such as an automobile moves, the magnetic field deforming region moves. If a ferromagnetic object such as an automobile approaches or moves away at a specific point, the direction and density of the geomagnetic field at that point will change, and the geomagnetic sensor installed at that point will detect the presence of the vehicle . Using these geomagnetic field features, geomagnetic sensors can be used to detect approach, passage, or stopping of vehicles, subways, trains, and so on.

For example, the number of vehicles passing through a particular point can be calculated. If the vehicle has information such as the intensity and direction of the earth's magnetic field at the point without moving the vehicle, it is possible to detect the vehicle passing through the point by measuring the intensity and direction of the earth's magnetic field when passing through the vehicle . However, the method of detecting a vehicle using a geomagnetic sensor is not a problem at all.

Fig. 1 conceptually shows a change in the earth's magnetic field caused by a vehicle, and shows a case where two vehicles 11 and 13 successively pass a specific point A, respectively. Since the vehicles 11 and 13 are also ferromagnetic, they have their own magnetic field deformation regions 11a and 13a. The magnetic-field-deformable regions 11a and 13a shown in FIG. 1 indicate the range in which the amount of change in the magnetic field is maintained to a significant extent for the detection of the vehicle, and may not directly indicate the range in which the earth's magnetic field varies. Generally, a vehicle of a typical size, such as a passenger car, causes a variation in the magnetic flux density around 3 μT to 25 μT when moving within a homogeneous geomagnetic field.

The problem is that, as shown in FIG. 1, when the two vehicles 11 and 13 are continuously moving, the magnetic field deformation regions 11a and 13a by the respective vehicles can overlap to become one continuous magnetic field deformation region. Therefore, the geomagnetic sensor installed at the point A recognizes one magnetic field deformation area that is larger than the two magnetic field deformation areas 11a and 13a. Therefore, Output the value. Eventually, an error occurs in the recognition of the vehicle.

On the other hand, the change in the magnetic field due to the ferromagnetic material becomes smaller as the distance from the magnetic material increases. Generally, when the distance between the sensor and the sensing object is doubled, the sensing signal is sharply reduced to about 1/8. Therefore, even in the case of the same ferromagnetic object, the change of the geomagnetic field recognized by the sensor depends on the distance between the sensor and the object. Even if a small object approaches the sensor, the change of the earth's magnetic field is largely recognized. If a large object is far from the sensor, the deformation of the earth's magnetic field is recognized to be very small.

In order to recognize the vehicle using the geomagnetic sensor, the magnitude information of the magnetic field signal is very important, and it is necessary to correct the attenuation of the geomagnetic field change amount according to the measurement distance between the vehicle and the sensor.

[Related Technical Literature]

1. Vehicle sensing device using geomagnetic sensor (Patent Publication No. 10-2001-0067701)

According to the present invention, an analog-to-digital converter (ADC) is used as a method for confirming that the vehicle has passed the geomagnetic sensor. In other words, while reading the measured value in real time using the analog-to-digital converter, a method of checking the point at which the value added / subtracted while the vehicle passes over the geomagnetic sensor is returned to the initial value before passing the vehicle is used. This method can not recognize the two vehicles in the situation shown in FIG. 1 separately.

An object of the present invention is to provide a vehicle sensing apparatus using a geomagnetic sensor and a vehicle sensing apparatus that corrects detection errors of the geomagnetic sensor using a distance sensor and a method of sensing the same.

It is another object of the present invention to provide a vehicle sensing apparatus and a sensing method thereof for preventing a vehicle recognition error by correcting a change amount of a geomagnetic field recognized by a sensor to a distance to the vehicle.

In order to achieve the above object, a vehicle sensing apparatus according to the present invention can detect a vehicle passing through a vehicle passage. The cars here also include trains. The vehicle sensing apparatus includes a geomagnetic sensor for measuring an intensity of a geomagnetic field at the vehicle passage, a distance sensor installed at an edge of the vehicle passage to measure a distance to an object passing through the vehicle passage, A geomagnetism change amount calculation unit for calculating a change amount of a geomagnetic field when the vehicle is traveling on the vehicle passage based on a magnitude of a geomagnetic field; (First condition) and whether the measured distance measured by the distance sensor is smaller than the first reference distance (second condition), and determines whether the first condition and the second condition are both satisfied And a vehicle sensing unit recognizing the presence of the vehicle in one case.

According to an embodiment of the present invention, the vehicle sensing unit may start detection of the vehicle when both the first condition and the second condition are satisfied, and if any of the first condition and the second condition is changed to the unsatisfactory condition It can be recognized that the vehicle has passed while terminating the detection of the vehicle. In this case, the vehicle sensing apparatus of the present invention further includes a passing vehicle calculating section that receives a signal corresponding to the sensing start and sensing end of the vehicle from the vehicle sensing section, and calculates the number of vehicles passing through the vehicle passage .

According to another embodiment, the geomagnetism change amount calculation unit may set a second reference distance smaller than the first reference distance. In this case, when the distance measured by the distance sensor is smaller than the first reference distance and is greater than the second reference distance, the geomagnetism change amount calculation unit may calculate a difference between the measured distance measured by the distance sensor and the second reference distance It is possible to calculate the amount of change of the geomagnetic field by correcting the intensity of the geomagnetic field measured by the geomagnetic sensor.

A method for detecting a vehicle of a vehicle sensing apparatus according to another embodiment of the present invention includes the steps of (1) measuring a strength of a geomagnetic field in the vehicle passage using a geomagnetic sensor, Measuring a distance to an object passing through the passage; (2) calculating a variation amount of the earth's magnetic field when the vehicle is passing through the vehicle passage based on the intensity of the geomagnetic field measured by the geomagnetic sensor; (3) whether or not the calculated amount of change of the geomagnetic field is equal to or greater than a reference change amount determined based on a vehicle of a predetermined size (first condition) and whether the measured distance measured by the distance sensor is smaller than a first reference distance (Second condition), and recognizing the presence of the vehicle when both of the first condition and the second condition are satisfied.

The vehicle sensing apparatus of the present invention recognizes the vehicle by detecting a change in the earth magnetic field caused by a vehicle (including a train) passing through a vehicle passage.

At this time, the vehicle sensing apparatus can separately recognize the passing vehicle even when the change of the earth's magnetic field is not classified by vehicle as the vehicle continuously passes through the distance sensor, and the number of vehicles passing through the vehicle passage It can be calculated accurately.

Also, even if the amount of change of the earth's magnetic field due to the vehicle passing a little distance from the geomagnetic sensor is not sufficient for recognizing the vehicle in a vehicle passage having a somewhat wide width, the geomagnetic field measured by the geomagnetic sensor By correcting the intensity, the problem of vehicle recognition error can be solved.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view conceptually showing a change of a geomagnetic field caused by a vehicle,
2 is a block diagram of a vehicle sensing apparatus of the present invention;
3 is a flowchart provided in the description of the vehicle sensing method of the vehicle sensing apparatus of the present invention, and
4 is a diagram provided in the description of a method for individually recognizing a vehicle when two vehicles pass successively.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to the drawings.

2, the vehicle sensing apparatus 200 includes a geomagnetic sensor M, a distance sensor P, a geomagnetism change amount calculation unit 201, a vehicle sensing unit 203, and a passing vehicle calculation unit 205, Not only can recognize the presence of the vehicle 11 on the vehicle passage, but also can accurately calculate the number of vehicles that have passed the vehicle passage. Here, the vehicle includes a train, a subway, and the like, which are means for moving the ferromagnetic body. Therefore, the vehicle passage is not necessarily limited to the road, but includes a railroad track.

The vehicle sensing apparatus 200 is provided in the form of a sensor module in which a geomagnetic sensor M, a distance sensor P, a geomagnetism change amount calculation unit 201 and a vehicle sensing unit 203 are embedded in one case .

The geomagnetic sensor M measures the intensity of the geomagnetic field near the installed area and provides it to the geomagnetism change amount calculation unit 201. The vehicle sensing device 200 can be installed at any place where the vehicle 11 passes (hereinafter referred to as a " vehicle passage ") such as a road or a vehicle access gate. Thus, the geomagnetic sensor M is normally installed at one side But it is sufficient to place it so as to be located in the field-deformable region 11a of the passing vehicle 11. [ Here, the magnetic-field-deformable region 11a may mean a region where the degree of change of the earth's magnetic field due to the passing of the vehicle 11 is maintained to such an extent that the degree of change of the earth's magnetic field is recognized as a vehicle detection by the processing method of the vehicle-

For example, in the middle of an area through which the vehicle passes, such as the specific point A in Fig. 1, and may be installed at one of the left and right edges of the vehicle passage as shown in Fig.

The distance sensor (P) corresponds to a sensor capable of measuring the distance to an object located at the front. According to the embodiment, the vehicle sensing apparatus 200 may use a so-called " object sensing sensor " capable of recognizing the presence or absence of an object such as an infrared sensor in place of the distance sensor P. [

The distance sensor P measures a distance (hereinafter, referred to as a 'measurement distance') to an object (a vehicle, a person, a motorcycle or the like) installed on one side of a vehicle traffic passage and periodically measures the geomagnetism change amount And the vehicle sensing unit 203, as shown in FIG.

The geomagnetism change amount calculation unit 201 receives the strength of the geomagnetic field from the geomagnetic sensor M on the vehicle passage, and calculates a change amount of the geomagnetic field in the vehicle passage. The geomagnetism change amount calculation unit 201 calculates the change amount of the corresponding geomagnetic field and provides it to the vehicle detection unit 203 .

According to the embodiment, the geomagnetism change amount calculation unit 201 corrects the intensity of the geomagnetic field based on the measured distance measured by the distance sensor P without directly using the intensity of the geomagnetic field read from the geomagnetic sensor M The amount of change can be calculated. The correction method of the geomagnetism change amount calculation unit 201 will be described below again.

The vehicle detection unit 203 basically determines whether or not the vehicle 11 has passed through the vehicle passage based on the amount of change of the earth's magnetic field calculated by the geomagnetism change amount calculation unit 201. [ For example, the vehicle detection unit 203 sets a reference change amount based on a vehicle of a predetermined size. When the change amount calculated by the geomagnetism change amount calculation unit 201 is equal to or greater than the reference change amount (satisfies the first condition) We judge that there is passage. The vehicle here is preferably a vehicle of the smallest size among the vehicles to be detected.

However, since the two vehicles 11 and 13 may be recognized as one vehicle when the two vehicles 11 and 13 pass one after another, as in the case of FIG. 1, 203 use a distance sensor P. The vehicle detection unit 203 detects a change amount of the geomagnetic field measured by the geomagnetic sensor M only when the measurement distance periodically measured and provided by the distance sensor P is smaller than the first reference distance If the measurement distance to the object is equal to or greater than the first reference distance (second condition unsatisfactory), the measurement value of the geomagnetic sensor M is determined to be invalid data and ignored. As described above, the vehicle sensing unit 203 recognizes that the vehicle is located on the vehicle passage (whether traveling) only when both the first condition and the second condition are met, so that the two vehicles 11 and 13 The vehicle detection unit 203 can detect two vehicle traffic.

Here, the first reference distance can be set to about the width of the vehicle passage to be detected.

The passing vehicle calculation unit 205 calculates the number of vehicles passing through the vehicle passage on the basis of the installation position of the geomagnetic sensor M and the distance sensor P by receiving the vehicle detection result from the vehicle detection unit 203.

Hereinafter, a vehicle sensing method based on the operation of the vehicle sensing unit 203 of the present invention will be described with reference to FIG. 3, with reference to FIG. 1. Fig. 4 is a view for explaining vehicle detection in the situation of Fig. 1, showing a first vehicle 11 and a second vehicle 13 passing in a direction of an arrow at a constant speed. As the first vehicle 11 and the second vehicle 13 successively enter, the magnetic field change regions by the two vehicles 11 and 13 overlap. The vehicle detection herein includes calculating the number of vehicles 11, 13 that have passed the vehicle passage, beyond simply recognizing the presence of the vehicle 11, 13 on the vehicle path. Hereinafter, a state in which the vehicle detection unit 203 starts recognizing the vehicle while the vehicle starts entering the vehicle passage is referred to as " vehicle detection start ", and a state in which the vehicle is not recognized again after the vehicle detection start is referred to as' Detection end '. Therefore, when one cycle leading to the start and end of vehicle detection is completed, one vehicle has passed.

<Calculation of change in measurement distance and earth magnetic field: S301>

The geomagnetic sensor M recognizes the magnetic field deformation region 11a formed around the vehicle 11 when the vehicle 11 passes through the vehicle passage where the vehicle sensing apparatus 200 is installed and the distance sensor P ) Will recognize the vehicle itself. Therefore, the measured value of the geomagnetic sensor M changes first, and the measured distance of the distance sensor P changes.

The geomagnetism change amount calculation unit 201 periodically calculates the amount of change of the geomagnetic field in the vehicle passage based on the strength of the earth magnetic field on the vehicle passage measured by the geomagnetic sensor M and provides it to the vehicle detection unit 203, The sensor P also measures the distance to an object on the vehicle passage and provides it to the geomagnetism change amount calculation unit 201 and the vehicle detection unit 203.

&Lt; Start of vehicle detection: S303 and S305 >

As described above, when the first condition and the second condition are both satisfied, the vehicle sensing unit 203 recognizes that the vehicle 11 exists on the vehicle passage, and recognizes that the vehicle 11 is in the 'vehicle sensing start' state. Therefore, the vehicle sensing unit 203 determines whether the geomagnetic variation amount provided by the geomagnetism change amount calculation unit 201 is equal to or greater than the reference variation amount (first condition) and whether the measurement distance provided by the distance sensor P is greater than a predetermined first reference (S303). If both the first condition and the second condition are satisfied, it is determined that the detection of the first vehicle is started (S305).

4, since the first vehicle 11 and the second vehicle 13 are moving at a constant speed, the time is proportional to the distance in the traveling direction regardless of the position of the distance sensor P or the geomagnetic sensor M. The progress can be indicated by t1 to t6.

At the time point t1, the first condition is satisfied because the amount of change of the earth's magnetic field by the first vehicle 11 is sensed. However, since the distance sensor P does not detect the first vehicle 11, The second condition is not satisfied because it is above the reference distance. Therefore, even if the intensity of the earth's magnetic field changes at the time t1, the vehicle detection for the first vehicle is not started. the first condition is still satisfied because the amount of change of the earth's magnetic field by the first vehicle 11 is maintained as it is at the time t2 and since the distance sensor P finally detects the first vehicle 11, The vehicle detection for the first vehicle is started.

&Lt; End of vehicle detection: S307 and S309 >

The vehicle detecting unit 203 recognizes that the vehicle 11 being sensed passes through the vehicle passage when any one of the first condition and the second condition is changed to unsatisfactory after the start of vehicle detection . Therefore, the vehicle sensing unit 203 determines whether the geomagnetic variation amount provided by the geomagnetism change amount calculation unit 201 is less than the reference change amount (first condition unsatisfactory), or if the measurement distance provided by the distance sensor P is the first (S307). If it is determined that the first condition or the second condition is unsatisfactory, it is determined that the detection of the first vehicle is terminated (S309).

In the case of FIG. 4, when the state of the vehicle is detected at time t2 and the state is maintained at t3, the amount of change of the earth's magnetic field by the first vehicle 11 is maintained and the first condition is satisfied. The vehicle is moved out of the distance sensor P so that the distance measured by the distance sensor P becomes equal to or greater than the first reference distance and the second condition is changed to the dissatisfied state. Thus, vehicle detection for the first vehicle is terminated.

Since the change of the earth's magnetic field by the first vehicle 11 or the second vehicle 13 is maintained at the time t4 and the first condition is maintained and the distance sensor P again detects the second vehicle 13 The second condition is satisfied again, so that the vehicle detection for the second vehicle 13 is started. At time t5, the second condition is again unsatisfactory as at time t3, and the vehicle detection for the second vehicle 13 is terminated. At time t6, both the first condition and the second condition are unsatisfactory.

&Lt; Counting the Number of Passed Vehicles: S311 >

When the vehicle detection unit 203 outputs a signal corresponding to the start and end of vehicle detection to the passing vehicle calculation unit 205, the passing vehicle calculation unit 205 determines whether the vehicle detection is started in step S305, It is recognized that one vehicle has passed, and the number of passing vehicles is counted.

In the case of Fig. 4, the vehicle sensing unit 203 generates a signal indicating that the vehicle is passing between t2 and t3, and generates a signal indicating that the vehicle is passing between t4 and t5. The passing vehicle calculation section 205 recognizes that the two vehicles have passed. Therefore, according to the method of the present invention, there is no problem that the magnetic field change regions of the two vehicles are overlapped and recognized as one vehicle passage as the two vehicles continue to pass like in the conventional case.

<Examples>

)에서의 자속밀도(

)는 다음의 수학식 1과 같다. A certain distance from the ferromagnetic body

) Of the magnetic flux density (

) &Lt; / RTI &gt;

은 자기 모멘트(Magnetic Moment), 그리고 μ₀는 공기의 투자율이다. 거리(

)는 강자성체의 형상의 가장 긴 부분의 3배 이상되는 거리이다. 수학식 1에서처럼, 지자기 센서(M)로부터 거리가 멀어지면 그 만큼 지구자기장의 세기가 작아지므로, 지구자기장 측정에 문제가 생길 수 있다. here,

Is the magnetic moment, and ₀ is the permeability of air. Street(

) Is a distance at least three times longer than the longest portion of the shape of the ferromagnetic body. As shown in Equation (1), as the distance from the geomagnetic sensor M increases, the intensity of the earth's magnetic field becomes smaller, which may cause a problem in the measurement of the earth's magnetic field.

In order to solve this problem, the geomagnetism change amount calculation unit 201 can correct the intensity of the earth magnetic field measured by the geomagnetic sensor M based on the measurement distance measured by the distance sensor P. [ This embodiment is preferable in the case where the width of the vehicle passage is wide and a part of the passing vehicle 11 can be excessively deviated from the geomagnetic sensor M. [ It does not need to be applied to a traffic route where only one vehicle can pass.

Hereinafter, for the sake of convenience of explanation, for example, it is assumed that a vehicle passage through which two vehicles can pass at the same time is described. At this time, it is assumed that the geomagnetic sensor M and the distance sensor P are installed at the edge of the vehicle passage, and the first reference distance is set to the entire vehicle width of the vehicle passage. Therefore, when the measured distance is equal to or greater than the first reference distance, the vehicle or the object does not pass.

The geomagnetism change amount calculation unit 201 may calculate the geomagnetic sensor change amount based on Equation 1 by using the distance measured from the distance sensor P to the vehicle 11 have. To this end, the geomagnetism change amount calculation unit 201 sets a second reference distance having a value smaller than the first reference distance. If the measured distance of the distance sensor P is smaller than the second reference distance, it means that the vehicle 11 and the geomagnetic sensor M are closer to each other. ) Is corrected only when the measured distance is smaller than the first reference distance and larger than the second reference distance. In other words, the greater the difference between the measured distance and the second reference distance, the greater the magnitude of the geomagnetic field measured by the geomagnetic sensor M (e.g., proportional to the third power of the difference). Here, the second reference distance may be set to a distance at which the vehicle can be sensed without correcting the intensity of the earth's magnetic field.

In the above description, the first condition and the second condition are described as one standard. However, depending on how the reference change amount is set, for example, the first condition may be changed as much as the "reference change amount" rather than the "reference change amount & It should not be construed as limited. The second condition is also the same as the technical idea of the present invention depending on how the first reference distance is set, but can be limited as different conditions. However, due to differences in the expressions, the scope of the present invention is not limited Should not.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be construed as limiting the scope of the invention as defined by the appended claims. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention.

Claims (8)

A vehicle sensing apparatus for sensing a vehicle passing through a vehicle passage,
A geomagnetic sensor for measuring an intensity of a geomagnetic field in the vehicle passage;
A distance sensor installed at an edge of the vehicle passage to measure a distance to an object passing through the vehicle passage;
A geomagnetism change amount calculation unit for calculating a change amount of a geomagnetic field when the vehicle travels on the vehicle passage based on the intensity of the geomagnetic field measured by the geomagnetic sensor; And
Whether or not the amount of change of the earth's magnetic field calculated by the geomagnetism change amount calculation unit is equal to or greater than a reference change amount based on a predetermined size of the vehicle (first condition) and whether the measured distance measured by the distance sensor is smaller than the first reference distance The second condition), and when the first condition and the second condition are all satisfied, the presence of the vehicle is recognized, so that even when the distance between the cars is short and the change of the earth's magnetic field by the two vehicles is not separated And a vehicle sensing unit capable of recognizing the two vehicles separately,
The geomagnetism change amount calculation unit calculates,
And a second reference distance that is smaller than the first reference distance, and when the measured distance measured by the distance sensor is smaller than the first reference distance and larger than the second reference distance, And calculates a change amount of the geomagnetic field by correcting the intensity of the geomagnetic field measured by the geomagnetic sensor by the difference of the second reference distance.
The method according to claim 1,
Wherein the vehicle-
When the first condition and the second condition are all satisfied, the detection for the vehicle is started, and when the first condition or the second condition is changed to the unsatisfactory condition, the detection for the vehicle is terminated And recognizes that the vehicle has passed.
3. The method of claim 2,
Further comprising a passing vehicle calculation unit that receives a signal corresponding to the detection start and the detection end of the vehicle from the vehicle detection unit and calculates the number of vehicles passing through the vehicle passage.
delete A vehicle detection method of a vehicle sensing apparatus that senses a vehicle passing through a vehicle passage,
Measuring a strength of a geomagnetic field in the vehicle passage using a geomagnetic sensor and measuring a distance to an object passing through the vehicle passage using a distance sensor installed at an edge of the vehicle passage;
Calculating a variation amount of a geomagnetic field when the vehicle passes through the vehicle passage based on the intensity of the geomagnetic field measured by the geomagnetic sensor; And
(Second condition) whether the measured distance measured by the distance sensor is smaller than a first reference distance (second condition), whether the calculated amount of change of the earth's magnetic field is equal to or larger than a reference change amount determined based on a predetermined- And recognizing the presence of the vehicle when both of the first condition and the second condition are satisfied, even if the distance between the cars is short and the change of the earth's magnetic field by the two vehicles is not separated The two vehicles can be separated and recognized,
Wherein the step of calculating the amount of change of the geomagnetic field includes:
And a second reference distance that is smaller than the first reference distance, and when the measured distance measured by the distance sensor is smaller than the first reference distance and larger than the second reference distance, And calculating a change amount of the geomagnetic field by correcting the intensity of the geomagnetic field measured by the geomagnetic sensor by a difference of the second reference distance.
6. The method of claim 5,
When the first condition and the second condition are all satisfied, the detection for the vehicle is started, and when the first condition or the second condition is changed to the unsatisfactory condition, the detection for the vehicle is terminated And recognizing that the vehicle has passed through the vehicle.
The method according to claim 6,
Further comprising the step of recognizing the presence of the vehicle and calculating the number of vehicles passing through the vehicle passage while repeating the step of recognizing that the vehicle has passed.
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