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3• USING TEXT MESSAGES TO CONTROL
3•5•2 TIMEROFF X AND TIMERON X COMMANDS
The commands TimerOff X and TimerOn X have the same functionality
as the global commands TimerOff and TimerOn described in chapter 3•4
but for the sole specified zone X (X = A, B or C).
3•6 SECURITY COMMAND: VIRTUAL
FENCE
The virtual fence commands allow to define a virtual zone identified
by the robot using its GPS position. The goal of these commands is to
enhance the security of the robot with respect to theft.
As soon as the robot will self identify to be out of the virtual zone, it
will send an Alarm_SMS 'out of zone' to the 'ALARM_PHONE'.
The user must define the virtual zone large enough so that it
completely encloses the normal operating zone defined by the wire.
The virtual fence is defined as a square (or rectangular) zone centred
at the position where the robot is located when it is receiving the
command. It is thus recommended to go with the robot in the middle
of its working zone and send the command.
THE GPS/GPRS MODULE
Below snapshots show SMS messages of TimerOff X command
applied to Zone
As the GPS accuracy can be affected by external factors (trees,
buildings,...), it is also recommended to take some margin in the
distance defining the fence so to avoid receiving false alarms.
When receiving the command, the GPS/GPRS module is already
taking some margin by adding 15 m to the parameter passed in
the command.
The virtual fence commands can only be sent by the 'ALARM_
PHONE'. If the ALARM_PHONE is not yet defined, it is set to
the number that issued the 'Setfence' command.
A confirmation SMS is sent to the caller.
The virtual fence is defined using the command 'SetFence'. The syntax
of the command is: SetFence [width in meters] [height in meters]
- When no arguments are given explicitly, the default width and height are
300 m.
- When only 1 argument is given, the zone is defined as a square.
15 m in both directions are automatically added by the system.
In order to ensure a maximum accuracy, when receiving the 'SetFence'
command, the GPS/GPRS module checks that the current GPS position
is accurate enough. If not the case, the confirmation SMS suggests
'Retry within 2 minutes'.
The virtual fence mechanism can be disabled by sending the command
'NoFence'.
A.
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