What is Garage mode?
With the garage option enabled, GPS will be blocked when the vehicle returns to the garage. You increase the initial delay if the vehicle is to be used in tunnels or where GPS will not be available for long periods, after the initial delay – the system will apply gentle velocity movements to maintain accuracy and will assume the vehicle is stationary. The GPS Control option is different because it tells the INS how long to ignore unexpected GPS measurements before being forced to believe them - it will not assume the vehicle is stationary and it will not apply velocity movements as does the Garage Mode.
What is the purpose of Garage mode?
The purpose of the “Garage Mode” is to stabilise (or reduce) the inertial drift when GPS is absent for a long period of time. If an Inertial Navigation System (INS) does not get regular position or velocity updates (from GPS), then it will start drifting: the drift increases with the time spent without updates (from GPS). The best method for reducing drift is to fit a wheel-speed sensor to the INS and to enable to “Advanced Slip” option. However this is not always possible as the customer may not be able to provide a wheel-speed input; this is where “Garage Mode” comes in.
What are the limitations of Garage mode?
What “Garage Mode” does is to tell the INS that its speed is somewhere around 0: if it is applied for a very long time it will cause the speed output by the INS to reduce close to zero; this is ideal for situations where the INS drives into a garage (and loses GPS) but comes to a standstill fairly soon (within a minute) of losing GPS – hence the name “Garage Mode”. The initial delay is really about deciding how long the vehicle is likely to drive in the garage before coming to a standstill. It is also possible to use “Garage Mode” in other conditions (city centre or in a tunnel) but although this will prevent the velocity from drifting to excessively large values, it will introduce an error by reducing the velocity when the vehicle may in fact be moving. This is why “Garage Mode” should be used with care and OxTS always recommends the use of a wheel-speed sensor instead.