Method for vehicle classification using multiple geomagnetic sensors

A method for vehicle classification using multiple geomagnetic sensors, wherein, the method comprises the following steps:

• 1) sequentially deploying N geomagnetic sensors on a road side at equal intervals d, and a vehicle sequentially passing by each of the sensors when it runs, wherein 2≤N≤10, 5 m≤d≤15 m;
• 2) N geomagnetic sensors respectively collecting magnetic field data around the sensors in real time and sequentially transmitting the magnetic field data to a data processing module, wherein the data processing module adopts a low-power-consumption microprocessor;
• 3) the data processing module analyzing the data transmitted by the N sensors:
• 3a) the data processing module judging whether or not a data mark sent by a first geomagnetic sensor indicates a vehicle:
• if so, judging that there is a vehicle passing by, and executing 3b), otherwise, returning to 2);
• 3b) the data processing module judging whether a data mark sent by a second sensor to a Nth geomagnetic sensor indicates there is a vehicle or not:
• if so, judging that there is a vehicle passing by, and executing 3c), otherwise, returning to 2);
• 3c) the data processing module storing data about the vehicle passing by sent by the first geomagnetic sensor to the Nth geomagnetic sensor, and adding a time stamp;
• 4) the data processing module aligning the stored data:
• 4a) finding out data at a time when the vehicle drives in the N geomagnetic sensors, and then finding out data at a time when the vehicle leaves the N geomagnetic sensors;
• 4b) respectively aligning data, i.e. first data, at an initial time when a vehicle drives in N geomagnetic sensors, and sequentially aligning second data, third data . . . and M data acquired by the Nth sensor when the vehicle drives in, until aligning the data acquired when the vehicle leaves the Nth sensor, wherein M is the number of data acquired by the sensor;
• 5) calculating a time difference Δt1,2, Δt2,3, . . . , ΔtN-1,N obtained when the vehicle passes by two adjacent sensors among N sensors:
• 5a) sequentially calculating a time difference between the first data and a time difference between the second data between the first and second sensors after alignment, and a time difference between the M data until a time difference between the last data is calculated;
• 5b) taking an average value of the time differences among all the data, i.e. a time difference Δt1,2 obtained when the vehicle passes between the first sensor and the second sensor;
• 5c) sequentially calculating a time difference between the first data, a time difference between the second data . . . , and a time difference between the M data between the second and third sensors after alignment, until a time difference between the last data is calculated;
• 5d) taking a mean value of a time difference among all the data, i.e. a time difference Δt2,3 obtained when the vehicle passes between the second sensor and the third sensor;
• 5e) repeating steps 5a-5d to sequentially obtain a time difference Δt1,2, Δt2,3, . . . , ΔtN-1,N between two adjacent sensors;
• 6) calculating an average time
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• 7) calculating a magnetic length of a vehicle when it passes by;
• 7a) setting an arrival threshold value and a departure threshold value of a vehicle, acquiring durations Δt1, Δt2, . . . , ΔtN of the vehicle when it passes by N geomagnetic sensors respectively according to the recorded time stamps, and calculating an average duration of the vehicle when it passes by each of the sensors:
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• 7b) calculating a magnetic length VML:
• VML=v×Δt′ of a vehicle when it passes by according to a running speed v of the vehicle and an average duration Δt′ of the vehicle when it passes by each of the sensors;
• 8) setting a Z axis magnetic field strength threshold value S, subtracting a geomagnetic base line from Z axis magnetic field data detected by N geomagnetic sensors respectively, and detecting whether data less than the threshold value S exist;
• if the N geomagnetic sensors exist, marking as ‘1’, otherwise, marking as ‘0’;
• 9) judging vehicle classification results:
• 9a) setting double-threshold values L1 and L2 of the vehicle magnetic lengths, and L1>L2;
• 9b) comparing the magnetic length of the vehicle when it passes by with L1 and L2;
• if the magnetic length of the vehicle is greater than or equal to L1 when it passes by, the vehicle is judged to be a large one;
• if the magnetic length of the vehicle is less than or equal to L2 when it passes by, the vehicle is judged to be a small one;
• searching and judging whether or not the mark corresponding to the current vehicle is ‘1’ if the magnetic length of the vehicle is smaller than L1 but greater than L2 when it passes by, the vehicle is judged to be a large one, otherwise, to be a small one.