What is a CORS (Continuously Operating Reference Station)?

A Continuously Operating Reference Station (CORS) is a reference station that provides continuous and permanent real-time positioning information for a specific area. These stations are equipped with high-quality GNSS receivers and antennas installed at precisely known locations.

The fundamental purpose of a CORS is to provide an unwavering and ongoing source of positional reference data by collecting raw satellite signals continuously. By constantly comparing its known spatial coordinates with incoming satellite data, CORS generates highly precise correction information that dramatically improves the accuracy of standard satellite positioning – from errors measuring several meters down to a matter of centimeters or even millimeters.

These stations are often networked across wide areas, forming the technical backbone behind high-precision positioning for mission-critical fields such as land surveying, GIS mapping, precision agriculture, civil engineering, robotics, scientific research, and autonomous vehicles. By delivering both real-time corrections (Real-Time Kinematic, or RTK) and post-processed data (Post-Processed Kinematic, or PPK), CORS networks accommodate a broad array of professional and scientific workflows that demand pinpoint accuracy. The reliability, stability, and constant operation of CORS systems have made them indispensable wherever exact spatial information is required, and many CORS networks (usually those provided by governemnt entities) further foster innovation by publicly sharing their data and correction streams.

What Makes a CORS Station Different from a Regular GNSS Receiver?

A CORS is distinguished from a standard GNSS receiver by several characteristics:

Precisely surveyed location: The antenna’s position is known to millimetre accuracy through geodetic survey. This known position is the reference against which atmospheric and satellite errors are computed.
High-quality hardware: CORS use survey-grade (geodetic) antennas and receivers with multi-frequency, multi-constellation capability. Better hardware equals cleaner observations and more accurate corrections.
Continuous operation: CORS run 24 hours a day, 365 days a year. They log observations at high rates (1 Hz or faster) and deliver them in real time to a correction server.
Environmental stability: CORS antennas are mounted on stable structures (concrete pillars, building rooftops) away from signal obstructions and multipath sources.
Reliable connectivity: Redundant internet connections ensure correction data reaches the processing server with minimal interruption.
Publicly accessible: Government-run CORS networks usually offer public access to data, enabling wider adoption and technological advancement in geospatial fields.

How CORS Stations Fit Into a Network RTK System

In a Network RTK system like Skylark Nx RTK, CORS stations perform the following role:

Data collection: Each CORS simultaneously tracks all visible GNSS satellites and streams raw observations to the central cloud server.
Error estimation: The server compares observations from all CORS to build a regional model of ionospheric delay, tropospheric delay, satellite clock errors, and orbit errors.
Correction generation: When a rover requests corrections, the server interpolates from surrounding CORS data to generate corrections tailored to the rover’s specific location.

Public vs. Private CORS Networks

CORS networks come in two types:

Public networks: Government-operated networks like NOAA CORS Network (USA), EUREF Permanent GNSS Network (Europe), and national networks in many countries provide free data for scientific and some commercial use. Coverage density and real-time data quality vary significantly.

Commercial networks: Private operators like Swift Navigation build proprietary networks with guaranteed uptime SLAs, denser station spacing, higher-quality receivers, and optimised server infrastructure. Commercial networks typically offer better coverage, reliability, and correction quality for precision commercial applications.

Read our comparison of public vs. private networks here: Free vs. Paid RTK Correction Services

Frequently Asked Questions

Do I need to install a CORS to use RTK?

Not with a Network RTK service. Providers like Swift Navigation operate the CORS infrastructure and sell access as a subscription. You only need a compatible GNSS rover with an internet connection. If you choose single-base RTK, you would set up your own base station — but this is not a true CORS, as it lacks the survey precision and continuous uptime of a commercial CORS.

How far apart can CORS stations be in a network?

Typical spacing is 50–100 km for Network RTK. Closer spacing improves atmospheric modelling accuracy and allows faster convergence. Skylark's proprietary atmospheric model can maintain high accuracy even with wider station spacing by using machine learning to model spatial ionospheric variation between stations.

What is the difference between a CORS and a VRS?

A CORS is a physical reference station with real hardware at a fixed location. A VRS (Virtual Reference Station) is a software-generated synthetic station near the rover's position, created by the Network RTK server by interpolating data from surrounding CORS. The VRS mimics a physical base station within metres of the rover, maximising correction accuracy.