Real-Time Kinematic (RTK) requires two receivers—a base and a rover. The rover is always positioned relative to the base. This means that the measurements taken by the rover are always relative to the position of the base. That’s why it’s important to pay special attention to the position of the base you set up. To better understand the effect of the base’s setup on the rover's measurements, let's take a closer look at its peculiarities.
Before you choose
Every survey requires a coordinate system setup which always depends on the base. To accurately represent the position of objects on Earth using coordinates, surveyors use special reference frames known as datums. The base is always tied to the datum and the datum should always be considered on the rover when setting up a coordinate system for a survey project.
This data is usually given in the technical assignment or official documents. In some cases, you can look it up in the EPSG Geodetic Parameter Dataset (also EPSG registry), a public registry of geodetic parameters. In the latter case, the decision should be based on the area you want to work in: for each region, there is a coordinate system optimized for this specific area.
The whole setup then ends with the project setup on your rover which requires specifying a coordinate system which is usually based on the datum of your base.
Learn more about the coordinate system setup in Emlid Flow & Emlid Flow 360 in the Introduction to the coordinate systems article.
In addition to paying special attention to the datum of the base, you should always consider the method you choose to enter the coordinates of the base.
Manual coordinates entry method
When the position of your base is known, its coordinates are entered manually. In this case, its position will be an exact point on the Earth’s surface and the rover will determine its position as a point with certain coordinates on the Earth’s surface too. This means that the accuracy of rover's measurements will be at centimeter level.
Setting up your base over a known point is the recommended base setup method if you want to get accurate and repeatable results with a reference to a particular area. You can get a known point in several ways:
- Work with the existing known point or benchmark,
- Work with an NTRIP service to get the known point,
- Work with the existing known point when you cannot place your base over it but you can place it nearby,
- Determine the coordinates of a point using static processing or post-processing services.
Averaged SINGLE coordinates entry method
When the position of the base is unknown, its coordinates can be averaged in SINGLE. Averaging is done in standalone mode without using any corrections and the position is determined within a radius of several meters. Each time you average the base's position, you'll get a point somewhere in that radius. This means that the rover's measurements will also be somewhere in that radius and the accuracy will be at meter level. See Figure 2 below.
This type of setup only works well if you need to measure the objects in relation to each other during a particular survey without a reference to a particular area. To reproduce it, you'll need to place the base over the same mark and enter the coordinates manually or pick them from the saved ones in Emlid Flow. Otherwise, you may end up with a different point that won’t fit your project and lead to coordinates mismatch. If you want to learn more about this method, check out our guide on using Average SINGLE coordinates entry method in Emlid Flow.