RTK NETWEST TECHNOLOGY
RTKnetwest own and operate a network of Continuously Operating Reference Stations (CORS). Using Virtual Reference Station (VRS) position-correcting software, RTKnetwest provide a positioning service with a real time accuracy of ±2cm.
Real-Time Kinematic (RTK) is a widely accepted technology for accurate positioning and navigation. Initially this method was based on a mobile GNSS rover connecting to a single base or reference station with known coordinates. The resulting positioning accuracy can be ±2cm. However, the accuracy, availability and reliability of positioning data when using a single base station for real time positioning was dependent on the distance between the base station and the rover. With increased distance, clock errors, satellite orbit errors and atmospheric signal delays are greater. These result in deviations to the accuracy of positioning.
A big breakthrough in performance and accuracy was achieved by networking base stations together. These networked base stations (or GNSS receivers) are permanent installations and continuously stream satellite observations to a central server. The server running specialised software performs calculations to further refine the rover position by creating a virtual base station that is closer to the rover. The distance between a GNSS rover and the corresponding base station is no longer an issue.
Users subscribe to an RTK network to receive RTK corrections with their rover instead of having to set up their own base station.
The RTKnetwest network is available 24 hours per day, 7 days a week and 365 days a year*. Data streaming of DGPS, CMR, CMR+, RTCM 2.3, RTCM 3.0 is supported in real-time and users can also retrieve stored GNSS and modelled VRS data from the central server via the internet for post-processing.
*Dependent on Telstra communication service and satellite availability
SOFTWARE
RTKnetwest utilise Pivot V3.1 the latest networked GPS software supplied by Trimble. This software is located on a dedicated server with redundant power supply and redundant internet connections. The Pivot software is the central processing core of the GPS correction service provided by RTKnetwest. Pivot manages all of the data streaming in from the 22 CORS stations, continually processes the baselines between these points, calculates rover positions and streams out the correction services. The Pivot software also manages and stores the raw data from all base stations for 3 months.
CORS TECHNOLOGY
A network of RTK base stations requires a recommended minimum of five stations (there is no maximum) with an inter-station spacing of up to 70 km. These networked base stations are fixed to the ground and continuously stream satellite observations, at 1 second intervals to software running on a central server. This is known as a CORS network. It consists of several GNSS RTK base stations interconnected by reliable communications to enable real time computations and control. Each station, as a minimum, requires a receiver, an antenna, a modem for communication and a power supply.
VIRTUAL REFERENCE STATION (VRS) TECHNOLOGY
Quality checks are performed by the software running on the central server on the continuously streamed data delivered by the base stations. Correction models are calculated and made available to users. Users connect into the system using a wireless mobile connection; the software acknowledges the users' field positions, applies corrections for ephemeris, tropospheric and ionospheric errors and generates a “virtual base station”, for that individual rover.
Users operate as though this virtual base station is right next to their rover. The software then produces a set of standard format correction messages as if they were coming from the virtual base station and transmits them to the rover.
As a result, errors are eliminated or significantly reduced, allowing users to achieve RTK precision of ±2cm continuously over much greater distances.
SINGLE BASE STATION TECHNOLOGY
RTKnetwest’s software also offers single base corrections which works similarly to a traditional RTK method with corrections supplied via an internet connection. This service is suitable for some of the remote CORS which do not form part of the network solution. In particular the areas of Albany, Nyabing, Hyden and Dowerin. All of the individual CORS stations can also be utilised as a Single Base Station.
REFERENCE DATA SHOP
RTKnetwest’s software manages and stores the raw data from all 23 CORS operating in the network. This raw data is available for download from the “Reference Data Shop” interface for subscribed users. Data can be selected at 1 second to 60 second intervals from any base station and any time period within the last three months and exported in a variety of formats including: RINEX 2.11, RINEX 2.10, RINEX 3.0, DAT, TGD, T01 & T02.
The “Reference Data Shop” now includes a very valuable feature of being able to create Virtual Reference Station Data. Subscribed users can now enter a coordinate central to their project area along with a time interval, and Reference Data will be created at that point from the three nearest CORS stations. This is a useful feature for reducing baseline length when post processing static GPS data.
The RTKnetwest network is available 24 hours per day, 7 days a week and 365 days a year. Data streaming of DGPS, CMR, CMR+, RTCM 2.3, RTCM 3.0 is supported in real-time and users can also retrieve stored GNSS and modelled VRS data from the central server via the internet for post-processing.
