Tech Chat | Which is better among Static Survey, RTK or PPK?
With the rapid development of the high precision GNSS industry, the GNSS surveys are becoming more and more popular worldwide. When selecting the GNSS products, we can see the static accuracy, RTK accuracy and PPK accuracy in the specifications. Of these common GNSS measurement methods, is the higher accuracy the better? What's the difference between these methods, and in which applications should we choose which corresponding method?
Static Measurement
GPS static measurement principle: According to the carrier phase observations measured by several GPS receivers tracking GPS satellite signals, using the method of difference, the coordinate difference between the observation stations is obtained, that is, the baseline vector. Then according to the known point coordinates and baseline vector to obtain the coordinates of other stations. Relative positioning can eliminate or greatly reduce errors (such as satellite clock errors, ionospheric delays, and process delays, etc.), so a high-precision relative position can be obtained, which is widely used in control measurements.
RTK
RTK (Real Time Kinematic) measurement system generally consists of three parts: GNSS receivers, data transmission system and dynamic measurement software system. RTK measurement technology is based on carrier phase observations and has a carrier phase differential measurement technology with fast and high-precision positioning functions. It can obtain the three-dimensional positioning results of the station in the specified coordinate system in real time, and has centimeter-level positioning accuracy.
The working principle of RTK measurement is: Set one GNSS receiver as the base station, and set up one or more receivers as the rover. The base station and the rover simultaneously receive the signals transmitted by the same GNSS satellite at the same time, and the observation value obtained by the base station is compared with the known position information to obtain the GNSS differential correction value. Then, this correction value is transmitted to the rover through the real-time data link to correct its GNSS observation value, so as to obtain the more accurate real-time position of the rover after differential correction.
PPK
The working principle of PPK (Post-Processing Kinematic) technology is to use a base station receiver and at least one mobile receiver to conduct synchronous observation of GNSS satellites. That is to say, the base station maintains continuous observation, and the initialized rover can move to the next point after measuring. During the movement, it is necessary to maintain continuous tracking of the satellite in order to transmit the ambiguity of the whole week to the point to be determined.
The data received by the base station and the rover synchronously are linearly combined in the computer to form a virtual carrier phase observation, determine the relative position between the receivers, and finally introduce the known coordinates of the base station to obtain the three-dimensional coordinates of the rover.
Static vs RTK vs PPK
| Survey Method | Static Survey | RTK | PPK |
|---|---|---|---|
| Quantity of GNSS device | At least 3 devices | At least 1 base + 1 rover | At least 1 base + 1 rover |
| Real-time Transmission | Not required | 4G/Radio | Not required |
| Measurement Time | ≥ 40 min | 1 – 10s per point | 1 – 10s per point |
| Processing time | Post-processing | Real-time processing | Post-processing |
| Working Range | ≥ 50 km | 10 – 20 km | ≥ 50 km |
| Positioning Frequency | Up to 50 Hz | 1 – 2 Hz | Up to 50 Hz |
| Positioning Accuracy | 2.5 mm + 1 ppm Horizontally 5 mm + 1 ppm Vertically |
8mm+1ppm Horizontally 15mm+1ppm Vertically |
2.5 mm + 1 ppm Horizontally 5 mm + 1 ppm Vertically |
| Applications | Control point survey | Detail survey & stakeout | UAV surveying & mapping |
According to the characteristics of different measurement methods, their application scenarios are also different. For the surveying project, the static survey with higher positioning accuracy can be used for control point survey. And RTK with fast and real-time positioning can be used for detail survey and stakeout tasks. As for the UAV surveying and mapping, PPK with 50Hz positioning frequency can meet the needs of its high-speed movement. Meanwhile, PPK does not require real-time communication, which can reduce the burden of UAVs and increase their endurance.
So which is better among static survey, RTK and PPK? It’s hard to judge. Just select the surveying method depending on your task characteristics, what fits is the best.
No matter for survey, RTK or PPK, are all supported by SingularXYZ products and software. Learn more about SingularXYZ products
https://www.singularxyz.com/Y1_Land_Surveying_Solution.html
