GPS/GNSS Calibration Services

GPS (Global Positioning System) is the United States-operated satellite navigation system — the one most people are familiar with. GNSS (Global Navigation Satellite System) is the broader term that refers to all satellite-based positioning systems worldwide.

In practice, modern positioning receivers are almost always multi-constellation GNSS devices, meaning they simultaneously receive signals from multiple satellite systems rather than GPS alone. This significantly improves positioning accuracy, availability, and reliability — particularly in challenging environments like urban canyons, dense tree cover, or deep construction sites where signal obstruction is a factor.

When we refer to GPS/GNSS calibration, we are calibrating the full positioning system your receiver uses — whether it relies primarily on GPS or draws from multiple GNSS constellations. The calibration process verifies positional accuracy against known reference positions and NIST-traceable standards regardless of which satellite systems the receiver is using.

RTK (Real-Time Kinematic) is a satellite positioning technique that dramatically improves the accuracy of GNSS measurements by using a fixed base station to correct the signal errors received by a mobile rover unit — typically achieving centimeter-level positional accuracy in real time.

A complete RTK system consists of several interdependent components:

• Base Station – a fixed receiver set up over a known control point that continuously calculates and broadcasts correction data

• Rover – the mobile receiver carried or mounted in the field that receives both satellite signals and correction data from the base

• Data Collector – the field controller or software used to log positions, manage workflows, and store measurement data

• Radios – the communication link that transmits correction data from the base to the rover in real time

Why does every component need to be calibrated? Because positional accuracy is only as good as the weakest link in the system. An error introduced by a misconfigured base station, a data collector with incorrect antenna offsets, or a radio causing communication latency will propagate through the entire positioning solution — often invisibly, with no warning to the operator.

Calibrating the RTK system as a whole — not just individual components in isolation — is what produces meaningful, defensible positional accuracy data. 

Positional accuracy describes how closely a GPS/GNSS system's reported position matches the true position of a point on the ground. It is typically expressed as a distance indicating the radius within which the true position is expected to fall with a defined level of statistical confidence.

Positional accuracy has two primary components:

• Horizontal accuracy – how accurately the system locates a point in the X/Y plane (latitude and longitude)
• Vertical accuracy – how accurately the system determines elevation (Z axis); vertical accuracy is typically two to three times worse than horizontal accuracy for most GNSS systems

How is positional accuracy measured? During calibration, we compare the GPS/GNSS system's reported positions against precisely established reference points with known, survey-grade coordinates. The differences between reported and known positions are measured, analyzed statistically, and reported in SI units with NIST traceability.

Several factors affect the positional accuracy a system can achieve in the field, including:

• Number and geometry of visible satellites (PDOP — Position Dilution of Precision)

• Multipath interference from nearby structures or terrain

• Atmospheric conditions affecting signal propagation

• Baseline distance between the RTK base station and rover

• Equipment quality and firmware version

Calibration frequency for GPS/GNSS equipment depends on several factors: the industry you operate in, the criticality of positioning accuracy to your work, how frequently the equipment is used, and whether the equipment has been subjected to any event that could affect its performance.

General guidelines by application:

• Construction and surveying: Most contractors and survey firms calibrate RTK systems annually, or at the start of a major project where positional accuracy documentation will be required. Equipment used daily in demanding field conditions may warrant more frequent intervals.

• Oil and gas and marine: Quality management systems in these industries often require calibration at defined intervals specified in the project quality plan — typically annually, but sometimes more frequently for critical applications.

• Nuclear construction: Calibration intervals are formally specified in the project quality assurance program and are non-negotiable. Equipment may need to be calibrated before use on a specific project regardless of its last calibration date.

• Automotive testing: Proving ground applications typically calibrate GPS systems before a test campaign or on a schedule defined by the testing protocol.

Beyond scheduled intervals, GPS/GNSS equipment should also be recalibrated after:

• Any significant physical impact or drop

• Firmware or software updates that affect positioning calculations

• Antenna replacement or changes to antenna height/offset settings

• An out-of-tolerance finding on a previous calibration

• Extended storage or periods of non-use

If you are unsure what interval is appropriate for your specific equipment and application, we can help you evaluate your situation and establish a calibration schedule that supports your quality management system and project requirements.