MyRTKnet: Get set and go!

Central Control KL

Hardware

The hardware for the CC KL configuration is shown in Figure 4.

The Control Centre consists of the following:
• GPSNet1 server for hot swap redundancy
• GPSNet2 server for hot swap redundancy
• Maintenance server for system monitoring and data archiving
• 3745 router for access to the Internet and GITN cloud
• HP Printer
• UPS to hold the system for 3 days backup
• Monitor for GPSNET Servers
• Monitor for GPStream Server
• KVM Keyboard for GPSNET Servers
• GPStream server for web server and data distribution
• Monitor for Maintenance Server
• 3COM 10/100/1000 switch to interconnect all components

Computer systems

The system comprises 3 HP Proliant servers and a single rack mount router computer, GPStream server. Each of these computers and their respective function are discussed below.

GPSNet servers

The VRS computers are server grade HP Proliant computers configured in a pure ‘hot standby’ mode and are designated as VRS primary and VRS secondary, GPSNet1 and GPSNet2 respectively. Each of the servers is on line with the VRS application running. Both servers receive data from all the reference stations, logging these RINEX data and deliver RTKnet corrections when connected. However, it is the function of the GPStream server to distribute the reference station receiver data to the GPSNet servers and controls which server get user requests for RTKnet or DGPSnet corrections. Since both servers are online, should GPSNet1 server fail to operate, any online field user receiving RTKnet or DGPSnet corrections will lose their connection and the line will hang up. As soon as the field user calls back in, the GPStream server will detect the failure of the GPSNet1 server and will pass the request from the user to GPSNet2 server. Since both servers would be continuously logging data, none of the logged RINEX data would be affected.

VRS router Computer – GPStream Server

The GPStream Server has two functions:
• To distribute the raw RT17 data in real-time from the reference stations the GPSNet1 and GPSNet2 servers.
• To route the requests from the users to the online VRS server.

User requests for RTKnet or DGPSnet
corrections are sent to the GPStream Server. The GPStream Server is in continual communication with both GPSNet servers and as aforementioned, can detect the failure of one in seconds. If GPSNet1 Server does not respond to the GPStream Server’s requests, it will forward the corrections’ request to the next server in its list, in this case the GPSNet2 Server. Since the GPSNet2 Server is already online and the ionospheric model computed, corrections will be delivered to the field user almost immediately.

The GPStream server is essential for the operations of the system; so it is built in a dual power supply rack mount chassis and uses RAID hot swap hard disks so as to minimize possibilities of failure.

Maintenance and Archiving Server

The maintenance and archiving server is used for archiving RINEX and alarm data to CD and for monitoring the physical status of the reference stations. An application running on the archiving machine will check the reference station status every 5 minutes. Also on this machine is an application that make at every second to check which users are logged onto the system. This data is logged so that phone billing records may be cross checked.

All computers are located in a 42U 19” rack with the GPSNet servers and the GPStream server sharing a monitor, keyboard and mouse via a KVM switch and the archiving/maintenance server having its own monitor, keyboard and mouse. All monitors, mice and keyboards are located at work table near the rack. Telnet access to the routers and remote sites are done from here.

Virtual Reference Station

Reference Station Connections

The Trimble 5700 has its serial ports 1 and 3 connected to the MOXA’s Terminal Server (TS) serial ports 1 and 2. The MOXA’s TS serial ports behave like TCP ports. MOXA TS serial port 1 is assigned TCP port 4001 and port 2 TCP port 4002. Both TCP/IP sockets that are connected to the GPS receiver’s serial ports are configured in ‘server’ mode which means they are waiting for connections from a socket client.

The GPStream server is configured to connect to the reference stations in socket client mode. This connection will initialize the receiver and start the RT17 data stream. It will then setup socket servers that can be connected to by the GPSNet servers to receive the streamed RT17 data. In this way both GPSNet servers will receive the data rather than only one. This connection will initialize the receiver and start the RT17 data stream.

Remote User RTK or DGPS Call In

GPSNet is configured in socket server mode for the RTKNet and DGPSNet modules. The remote user will use the registered Telco Mobile Phone Internet Connection through GSM or GPRS to access the Control Centre KL. When a call comes in, the router will authenticate the user before connecting to the system, by using the username and password. If it is in the authorization database, the connection is allowed to proceed, else the line is dropped. When the connection proceeds the router brings the line up and immediately connects to the appropriate socket on the GPStream server. The GPStream server then queries both of the available servers. If they both answer, the request is sent to GPSNet1 server. If only the secondary answers the request is then sent there. The GPStream server will continue to forward requests to and from the GPSNet servers. The field user is now connected and following the reception of a GGA NMEA string by the GPSNet server, GPSNet will begin sending RTK or DGPS corrections from a ‘virtual base’ whose coordinates are based from the field user submitted GGA string.

Archiving/Monitoring

User accounting will be done from the archiving and maintenance server. An application will make query every second to check when users connect and disconnect to the server. The time the connection was initiatedand the time the connection was terminated will be logged to a file.

Hot Swap

The system proposed runs the GPSNet servers in a ‘hot standby mode’ in which the secondary GPSNet2 server is up, connected to the reference stations and running VRS. The GPSNet2 server is also logging RINEX data along with the primary GPSNet1 server. The only thing that will happen when GPSNet1 sever fail is that the GPStream server will forward RTKnet and DGPSnet corrections’ requests to the GPSNet2 server. Thus, switching to the standby system will be done in seconds after the fault is confirmed rather than the 20-30 minutes with the clustering solution.

MyRTKnet SERVICES

VRS Correction

a) Within the limits of our MyRTKnet Dense Network, MyRTKnet provides VRS GPS corrections with an accuracy of 1 to 3 cm horizontally and 3 to 6 cm vertically.

b) Distance dependent errors are considerably minimized with utilization of the MyRTknet network, thereby achieving increased accuracy and reliability.
c) RTK Surveying works at its optimum with a base station network to achieve the pinnacle of RTK Technology production potential.

Static Correction Data

a) Within the larger limits of the Single Base Station Coverage, MyRTKnet Solutions provides data for post-processing of static survey sessions, enabling positioning in the order of 1 cm or even millimeter recovery limit. The data is provided in the standardized RINEX format and is available via our password protected internet website.

b) Information with a data rate of 1- 15 seconds is stored indefinitely.

c) Post-processing provides the highest accuracy and is suitable where increased precision is required.

DGPS Correction

a) This application is a submeter Mapping and Navigation Technology.

b) The service provided by MyRTKnet Solutions includes data for postprocessed positioning and Real Time Correction. Any receiver that is capable of Real Time Corrections and cell phone data service can be used to receive MyRTKnet Solutions’ Real Time RTCM corrections.

c) Distance dependant errors are eliminated for users’ observations due to MyRTKnet Solutions’ array of base station locations.
• Mapping and Navigation
• Other Sub-Meter Uses

Hardware Requirement

MyRTKnet Solutions correction can be applied to any mobile receiver capable of connecting to a data cell phone. Cell phone reception, therefore, is a requirement of the VRS correction service. Presently, there are

mobile receivers which has both the capabilities of wireless connection to the cell phone and data collector. Any single or dual frequency GPS receiver can be used to collect data and for static correction data application, postprocessing software package is needed to reduce the data to final position that uses standard RINEX files.