User's Manual Part 1
92 OEMV Family Installation and Operation User Manual Rev 5B
Chapter 5 Positioning Modes of Operation
5.5.1 Real-Time Kinematic (RTK)
RT-2 (OEMV-2 and OEMV-3 with AdVance RTK) and RT-20 (OEMV-1 and OEMV-1G) are real-time
kinematic software products developed by NovAtel. They can only be used in conjunction with
NovAtel GPS receivers. A quick comparison of RT-2 and RT-20 is shown in Table 17 below.
Table 17: Comparison of RT-2 and RT-20
NovAtel’s RTK software algorithms utilize both carrier and code phase measurements; thus, the
solutions are robust, reliable, accurate and rapid. While both RT-20 and RT-2 operate along similar
principles, RT-2 achieves its extra accuracy and precision due to its being able to utilize dual-
frequency measurements. Dual-frequency GPS receivers have two main advantages over their single-
frequency counterparts when running RTK software:
1. resolution of cycle ambiguity is possible due to the additional information
2. longer baselines are possible due to the removal of ionospheric errors
Depending on the transmitting/receiving receivers and the message content, various levels of accuracy
can be obtained. Please refer to the particular accuracy as shown in the following table:
Table 18: Summary of RTK Messages and Expected Accuracy
The RTK system in the receiver provides two kinds of position solutions. The Matched RTK position
is computed with buffered observations, so there is no error due to the extrapolation of base station
measurements. This provides the highest accuracy solution possible at the expense of some latency
RT-2 RT-20
GPS Frequencies Utilized
L1 and L2 L1
Nominal Accuracy
1 cm (RMS) 20 cm (RMS)
Lane Searching
L1/L2 None
Message Formats
Transmitting
(Base)
Receiving
(Rover)
Accuracy
Expected
L1 and L2 RTK:
RTCAOBS with RTCAREF
RTCM Types 18 and 19 with
Types 3 and 22
RTCM Types 20 and 21 with
Types 3 and 22
CMROBS with CMRREF
L1/L2 RT-2 1 cm +1 ppm
RMS (RT-2)
RT-20 20 cm RMS
(RT-20)
L1 only RT-2 or RT-20 20 cm RMS
(RT-20)
L1 RTK:
RTCM Type 59 with Type 3
L1/ L2 or L1 only RT-2 or RT-20 20 cm RMS
(RT-20)
L1 Pseudorange Corrections:
RTCM Type 1
RTCA Type 1
L1/L2 or L1 only Any differential
enabled OEMV
0.45 m RMS
(DGPS)