Eventually, this system was abandoned, but the experience gained by both teams led to the establishment of the Sydnet system in Sydney, and SiReNT in Singapore.
SiReNT works in three modes: differential correction to any one of its five base stations, Real Time Kinematic – which enables sub-metre positioning on the move – and post processing, requiring an internet connection.
Post processing is the most accurate. Khoo says that with one hour’s occupancy, the position is sufficiently accurate to conform to Singapore’s requirements for legal traceability of position.
However, less than half of local land surveyors have taken up the system. Khoo says the price – $1200 per annum or 50c/min – may be to blame, rather than the innate conservatism of surveyors.
The most interesting part of the SiReNT project is that it uses GPRS to communicate its RTK corrections. GPRS gives internet connectivity over a standard GSM telephone connection.
This is already in demand for machine guidance applications, says Julia Tan, the operations and marketing manager at GPS Lands, the local Trimble distributor. She says it may also provide a communications channel for information from traffic management authorities.
Authorities in Singapore are considering the idea of moving to a pay-per-kilometre charging system to replace an annual usage fee. GNSS would track the movement of vehicles and fees would be based on the distance travelled.
Such a system could also be tied to traffic management systems, enabling drivers to track congestion, so they can delay travel, or use alternative routes.
