Every GNSS receiver must estimate the distance between itself and the satellites overhead. The quality of those distance measurements ultimately determines the accuracy of the calculated position.

Professional GNSS receivers use two different observation methods: pseudorange measurements and carrier phase measurements. While both are essential, they serve different purposes and offer very different levels of precision.

Pseudorange is the measurement method used by most navigation devices, including smartphones, vehicle navigation systems, and recreational GPS units.

The receiver calculates the travel time of a satellite signal and multiplies it by the speed of light to estimate the distance between the satellite and the receiver.

This method has several advantages:

• Fast initialization
• Reliable under most conditions
• Suitable for real-time navigation

However, even very small timing errors translate into noticeable positioning errors on the ground. As a result, standalone pseudorange positioning typically delivers horizontal accuracy in the range of 3 to 10 meters, depending on satellite visibility and environmental conditions.

For applications such as vehicle navigation, outdoor recreation, or fleet tracking, this level of accuracy is more than adequate. For engineering surveys or construction layout, however, it is far from sufficient.

RTK surveying relies on a far more precise observation known as carrier phase measurement.

Instead of measuring only the travel time of the satellite signal, the receiver tracks the phase of the carrier wave itself. Because the wavelength of the GNSS carrier signal is only a few centimeters long, it can detect position changes with millimeter-level sensitivity.

The challenge is that the receiver initially does not know how many complete carrier wave cycles exist between the satellite and the antenna. This unknown value is referred to as the integer ambiguity.

Resolving these ambiguities is the key to RTK positioning. Once the receiver successfully fixes the integer ambiguities, it can continuously calculate positions with centimeter-level precision.

This is why professional surveyors always monitor the receiver status. A FIX solution indicates that ambiguities have been resolved and the receiver is operating at full RTK accuracy, while a FLOAT solution means the ambiguities are still being estimated and positioning accuracy is lower.

The biggest difference between conventional GNSS positioning and RTK is not the satellite system itself—both use the same satellites. The difference lies in how positioning errors are corrected.

RTK introduces a second receiver, known as the base station, which is installed over a point with accurately known coordinates.

Because the base station already knows its exact location, it can compare its calculated position with its true coordinates. The difference between the two represents the combined effect of satellite orbit errors, atmospheric delays, clock offsets, and other common error sources.

These correction values are then transmitted to the field receiver, commonly called the rover, in real time.

Depending on the project, correction data can be delivered through:

• Integrated UHF radio
• NTRIP over a cellular network
• Local CORS (Continuously Operating Reference Station) services

Since both the base station and rover observe nearly the same satellites at nearly the same time, most common errors affect both receivers similarly. By applying the correction data, the rover can remove the majority of these errors and calculate a far more accurate position.

This differential correction process is what enables RTK to consistently achieve centimeter-level accuracy in real time.

Although RTK positioning involves advanced mathematical models, the field workflow is straightforward and can be completed within minutes.

The survey begins by placing a base receiver over a known control point or connecting to an existing CORS network. The base continuously observes satellite signals and calculates real-time correction information.

Correction messages are sent to the rover using either UHF radio or an internet connection via NTRIP.

The communication method depends on the project environment. Radio communication is often preferred on remote construction sites or in areas without reliable mobile coverage, while NTRIP is widely used in urban regions served by permanent reference station networks.

The rover begins tracking satellites while simultaneously receiving correction data from the base.

Modern multi-frequency receivers can often achieve a fixed RTK solution within several seconds under favorable satellite conditions.

Once the receiver reaches a FIX solution, surveyors can begin measuring control points, property boundaries, topographic features, or construction stakeout locations with confidence.

Throughout the survey, the receiver continuously updates its coordinates in real time, allowing field crews to work efficiently without lengthy post-processing.

Actual RTK performance depends on satellite geometry, baseline distance, environmental conditions, and communication quality. Under normal surveying conditions, professional RTK GNSS receivers typically achieve:

These performance levels make RTK suitable for projects where even a few centimeters of error could lead to costly rework or construction delays.

It is important to note that published specifications assume favorable observing conditions. Dense tree canopy, severe multipath, poor satellite geometry, or unstable correction links may temporarily reduce performance. Experienced surveyors routinely verify FIX status and monitor quality indicators such as PDOP before recording critical measurements.