RTK Precision Positioning¶
Real Time Kinematic (RTK) is a precision satellite positioning technique which utilizes a base station to transmit position corrections to a receiver. The Inertial Sense RTK solution provides centimeter level position accuracy.
To use RTK, a base station, arover (receiver), and a method to send corrections from the base to the rover are required.
See the multi-band GNSS section for details on using our multi-frequency ZED-F9 GNSS system.
RTK Hardware Setup¶
Base Station Options¶
Any of the following devices can be used as a RTK base station. All Inertial Sense base station options require a GPS antenna.
- Inertial Sense EVB 2 - Sends corrections using the onboard 915 MHz radio, the onboard WiFi module, either serial port, or USB.
- Inertial Sense µINS module, EVB 1 or Rugged - Sends corrections on either serial port or USB that can then be forwarded to a rover using a communication method of choice.
- 3rd Party Base Station - e.g. Emlid Reach Receiver.
- Public NTRIP Caster - e.g. CORS Network.
The following configurations can be used for the RTK rover:
- Inertial Sense EVB 2 - Can receive corrections via the onboard 915 MHz radio, onboard WiFi module, serial ports, or USB.
- Inertial Sense µINS module, EVB 1 or Rugged - Can receive corrections via either serial port or USB.
Base to Rover Communication¶
- Direct Serial - Using USB, RS232, RS422/485, or TTL to pass corrections from Base to Rover.
- Radio Link - Inertial Sense EVB 2 uses the Digi Xbee Pro SX module to send RTK corrections. Other communication methods such as Bluetooth may also work for the chosen application.
- NTRIP - Transmits RTK correction data over the Internet. To receive messages with NTRIP, the user must supply a URL, port number, and mount point . Often a username and password are also required.
- TCP/IP - A protocol for communicating directly between computers. In order to receive messages using TCP/IP, an address (IP Address or DNS) must be suppled to the Base where the corrections will be transmitted.
How to Know RTK is Working¶
Using the EvalTool¶
- Connect the µINS Rover to a computer with the EvalTool running. Open the comport for the unit in the Settings > Serial Ports.
- Navigate to Settings > RTK.
- Under the Status section, RTK functionality can be verified in 3 ways:
- Status field will show Single. Over the course of several minutes this status will change to Float then Fix.
- The Differential Age will show a timestamp that increments and resets back to zero about every second. This shows that the Rover is receiving Base messages.
- The Accuracy: H, V will show a large number at first. This number will decrease over time as the system acquires RTK Fix. Once in Fix, this number will average at +- 0.08, 0.14 m.
Using the CLTool¶
- Connect the µINS Rover to a computer with the CLTool running.
- Include the argument -msgPresetPPD in the CLTool command.
- Observe the DID_GPS_RTK_NAV message, Status: 0x******** (Single) over the course of several minutes this will change to (Float) then (Fix).
RTK Fix Status¶
The LEDs on the IMX will indicate RTK fix status.
|3D Fix, RTK Float||Allows improved accuracy up to ~1m|
|RTK Fix||Allows increased accuracy up to ~3cm|
RTK Positioning Valid Flags¶
The RTK precision positioning fix status can be identified using the valid bit in the INS and GPS status flags.
// INS status INS_STATUS_NAV_FIX_STATUS(DID_INS_1.insStatus) == GPS_NAV_FIX_POSITIONING_RTK_FIX // GPS status DID_GPS1_POS.status & GPS_STATUS_FLAGS_GPS1_RTK_POSITION_VALID
RTK precision positioning fix is indicated is indicated when the RTK-Pos radio button turns purple in the EvalTool INS tab.
Progress and Accuracy¶
The ambiguity resolution ratio,
arRatio, is a metric that indicates progress of the solution that ranges from 0 to 999. Typically values above 3 indicate RTK fix progress.
DID_GPS1_RTK_POS_REL.arRatio // Ambiguity resolution ratio
The DID_GPS1_RTK_POS_REL status can be monitored in the EvalTool GPS tab.