Tech Chat – What’s the difference between RTK & RTD?
In order to obtain higher accuracy of GNSS, we usually use DGPS (Differential Global Positioning System) to help improve accuracy. Both using the differential data to correct GNSS positioning, what’s the main difference between RTK (Real Time Kinematic) and RTD (Real Time Differential)? And what are the differences in their application fields? Let's discuss it in today's blog.
RTD (Real Time Differential)
As a type of DGPS technology, RTD also consists of ground base stations and rovers. The rover receives the correction data sent by the base station to improve the positioning accuracy. The main difference is in the content of the correction data.
RTD calculates the true distance based on the known coordinates of the reference station and the coordinates of each satellite, and calculates the pseudo-range from each satellite to the reference station at each moment. Then compare it with the measured pseudo-range, deduce the pseudo-range correction number and send it to the user receiver, which is a code (C/A, P) difference technology.
Since RTD uses pseudo-range code difference, which does not have high requirements for ionospheric errors, the base station range is up to 100km, and it's easy to fix. The accuracy of RTD positioning is typically sub-meter level.
| Pseudo-range code | C/A | P |
| Length period of pseudo-noise code | 1023bit | 1023bit |
| Code element width | about 293.1m | 29.3m |
| Repetition period of pseudo-noise code | 1ms | 0.097752μs |
| Clock pulse rate | 1.023Mbit/s | 10.23 Mb/s |
RTK (Real Time Kinematic)
For RTK, although the working principle is roughly the same as that of RTD, the content of its correction data is more advanced. RTK calculates the carrier phase observation value of two stations, that is, sends the carrier phase collected by the base station to the user receiver, and solves the coordinates through difference data, which belongs to the carrier (L1, L2, L5) phase difference technology.
As shown in the figure below, since the code rate of the carrier is higher than the pseudo-range, the positioning accuracy of RTK is also higher, usually up to centimeter level. But on the other hand, RTK is more difficult to fix than RTD, and its cost is also higher.
(a) Code (P), (b) Code (C/A)
(c) Carrier phase
Fig. 2 Waveforms of different codes
Conclusion
In summary, both RTD and RTK belong to DGPS. The accuracy of RTD can reach the sub-meter level, and it is more cost-effective, which can be used in projects with moderate accuracy requirements such as vehicle navigation and agricultural spraying. But if you need higher positioning accuracy, RTK will be a better choice for land surveying, machine guidance, etc.
| Method | RTD | RTK |
| DGPS | √ | √ |
| Differential Technology | Code (C/A, P) | Carrier phase (L1, L2, L5) |
| Accuracy | Meter level or sub-meter level | Centimeter level |
| Working Range | >100km | >20km |
| Fixed Difficulty | Easy | Moderate |
Nowadays, with the rapid development of the GNSS industry, the RTK technology is more advanced than before. With full constellation tracking, 2.5cm accuracy, high fixed rate even in harsh environments, SingularXYZ team keeps making RTK products and solutions more cost-effective and easy-to-use.
Learn more about SingularXYZ RTK products and solutions
https://www.singularxyz.com/Y1.html
https://www.singularxyz.com/SAgro100_Automated_Steering_System.html
https://www.singularxyz.com/SV100.html
