CORS Network in India: How Survey of India Network RTK Works

What is a CORS network?

CORS stands for Continuously Operating Reference Stations: GNSS receivers fixed on stable monuments with precisely known coordinates, logging data all day, every day. A network links them to a central server that models the errors in GPS signals and other satellite signals across the region. A rover anywhere inside then receives corrections tailored to its own location instead of from one distant base.

What does the CORS network in India offer?

Survey of India runs the national system, opened to public and commercial users in 2023 with over 1,000 stations. Its published procedures cover:

• registration through a CORS registration form before access is granted;
• network RTK (NRTK) surveys in real time, with corrections in the open RTCM 2.4 and 3.2 formats and an accuracy of about ±3 cm;
• DGNSS surveys, the multi-constellation form of the differential global positioning system, and continuous topographic NRTK surveys;
• online post-processing and virtual reference station (VRS) data downloads.

Survey of India's own guidance mentions station spacing of about 60–70 km for network RTK. Corrections reach the rover over mobile internet, so the service is only as good as the data signal on site. The satellites behind it all are introduced in GNSS Explained for Surveyors.

When do we use CORS, and when our own base?

Many control jobs also need buried services checked along the line; calculate metres × rate yourself in our online tool.

A field scenario: a layout on the edge of the Aravallis

On a residential layout at the south edge of Faridabad, CORS network RTK handles the open plots and our own base takes over in the hills. The rover connects through the registered account, receives a correction stream generated for its own location and fixes within a minute on the flat ground near the road. Three hundred metres up the slope the mobile signal fades, corrections stop arriving and the rover drops to float. Instead of waiting, the crew sets a base station on a point already fixed through the network and finishes by radio. Both sets of points then sit in the same national frame, because the base itself was tied to it.

Common mistakes when relying on CORS

The network does its job well; the slips happen in how its results are used.

• Mixing frames or epochs. Points from an older survey in a different realisation can differ from new CORS results by several centimetres or more.
• Forgetting that heights are ellipsoidal. A network fix gives height above the ellipsoid; drawings normally need mean sea level.
• Planning without checking coverage. No data signal means no corrections, whatever the network's station count.
• Expecting more than the stated accuracy. About ±3 cm is the published figure; it is not a 1 cm service.
• Skipping check points. A network connection does not prove that the antenna height or the stored codes are right.

How CORS use is recorded in our reports

Each Mezux control sheet names the correction source for every point. Points fixed by Survey of India network RTK, by our own base, or by static sessions processed against CORS data are flagged separately. Each sheet also gives the frame, the geoid model applied for levels and the residuals on independent check points. The correction streams use RTCM formats delivered over NTRIP, and receivers can be field-tested by the ISO 17123-8 procedure for RTK equipment, which we follow for periodic checks.

Why does it matter for the client?

Because coordinates from satellite-based positioning tied to the national network agree with other surveys tied to it. A layout fixed this year and an extension surveyed in three years can match without hunting for an old site pillar, provided both record the same frame and epoch. For heights, a CORS-based value is still ellipsoidal; for drainage and plinth levels we carry levels from a known mark, as our guide to the survey benchmark (BM) explains. Final figures go into the output listed under what you receive from a total station survey.

To plan control for your site, ask for a quotation for your project.

Frequently asked questions

Is the Survey of India CORS service free?

Access requires registration and Survey of India sets its own terms for subscriptions; check its official CORS pages before relying on it for a project.

Can a phone use CORS corrections?

Ordinary phones cannot use them for centimetre work; a survey-grade GPS receiver and controller are needed.

What does a DGPS survey with CORS cost?

It depends on area and points, and on how the DGPS works on that site: network RTK, own base or static. See what a DGPS survey costs.

Do I need internet on site for CORS RTK?

Yes. Real-time corrections arrive over mobile data, so the rover needs a working connection for the whole time it is measuring.

Can CORS data be used after the survey?

Yes. Logged raw observations can be processed later against network data, which suits primary control where real-time fixes are not required.

Why do CORS and own-base results differ by a few centimetres?

Each carries its own small error, and the own-base values depend on how the base point was fixed. Tying the base to the network keeps the difference small.

Is network RTK good enough for boundary corners?

In most cases, for plots in open ground. Each corner must be fixed, checked by a second occupation and tied to the same frame as any earlier survey of the land.

What is a virtual reference station?

A set of correction data computed by the network for a point close to the rover, as if a base stood there. It shortens the effective baseline and improves the fix.

Written by Saniya Parveen · Technically reviewed by Rahul Rai · Updated 8 November 2026