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How electronic fences work

创建于01.20
//working principle/electronic fence
1. How does an electronic fence work?
As shown in the figure, the administrator specifies a series of coordinate data on the server in advance to define the scope of the electronic fence.
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  • The positioning device regularly reports its location data to the server, which includes coordinate data and positioning time. The server compares two adjacent location data with the range of the electronic fence, and infers whether the device has entered or left the fence based on the comparison result:
  • If the previous location data is within the fence and the next location data is outside the fence, the "leave fence alarm" will be triggered.
  • If the previous location data is outside the fence and the next location data is inside the fence, the "enter fence alarm" will be triggered.
  • If the previous and next data are both within the fence, or both are outside the fence, no alarm will be triggered.
Taking Figure 1 as an example, the two adjacent positions reported by the device are position points A and A1. If A is outside the fence range and the position point A1 following it is within the fence range, the "enter fence alarm" is triggered.
The two adjacent bits reported by the device are position points B and B1. If B is within the fence range and the following position point B1 is outside the fence range, the "leave fence alarm" is triggered.
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(Figure 1)
2. How do false alarms/missed alarms/delayed alarms occur?
If the device uploads location data at a long interval, or the device fails to locate itself because it enters a building, culvert, valley, or high-rise building, the two adjacent location data may be far apart. The device may have actually passed through the fence, but the two adjacent location data received by the server are both outside the fence, so no alarm is triggered, resulting in missed reports.
As shown in Figure 1, the coordinates of C and C1 are both outside the fence, so no fence alarm will be triggered. In fact, the device has crossed the fence between the two data, but the server cannot know the actual movement path of the device based on C and C1, so it causes missed alarms.
3. Is the electronic fence a device-side function or a server-side function?
Electronic fence is a software function on the server side. Its data processing is all done on the server side, and no calculation is required on the device side. The location data processed by the electronic fence comes from the device. As long as the device reports its location data to the server regularly, the server can implement the electronic fence function.
4. Will positioning accuracy affect the accuracy of fence alarms? How can I improve the accuracy of alarms?
Yes. Each positioning method is affected by many different factors, and the positioning accuracy obtained is different. Because the positioning accuracy is not high enough, the location data reported by the device may be far away from its actual location, which may cause the server to miss, misreport, or delay the alarm. In addition, if the device uploads location data at a large time interval (for example, every 30 minutes), the accuracy of the electronic fence alarm will also be reduced. Considering that increasing the positioning frequency usually results in greater power consumption, it is necessary to comprehensively consider the wearer's actual usage scenario and the battery capacity of the device to set an appropriate positioning frequency.
In addition, when the device is in a building, culvert, valley, mine or a narrow street between tall buildings, the GPS signal will be blocked and positioning will fail. If the positioning accuracy obtained by Wifi positioning is not enough, you can consider using Bluetooth beacons for auxiliary positioning.
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Thinkrace has developed positioning and geo-fencing functions based on Bluetooth beacons. Please contact us for more information.

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