On a recent survey project, the team discovered the local CORS tower was offline. Luckily they were able to use the free Emlid Caster service to share NTRIP corrections from a local base – via the Internet.

What is CORS?

A Continuously Operating Reference Station or CORS network, consists of stationary GNSS receivers that continuously collect satellite data. Users apply these corrections to their GNSS data, achieving highly accurate positioning for applications like surveying and mapping. AUSCORS is a free CORS service provided by the Australian government.

Tower offline

In some parts of Australia there are plenty of reference stations around. Private services such as HxGN or the free AUSCORS services can provide options to select an alternative reference point. In the case of Cooktown, there are no local alternatives that would satisfy our teams preference for a short baseline between our GNSS Base and Rover.

A short baseline?

A GNSS Base and Rover setup involves two GNSS receivers working together for high-precision positioning:

In the context of GNSS, a baseline is the vector between a GNSS base station and a rover. It represents the difference in their positions and is calculated by comparing the satellite data collected by both receivers.

Longer baselines introduce more error – so the shorter the baseline, the better!

Tower offline – but still have Internet?

With the local CORS tower offline, one option was to get corrections using a standard base and rover setup. The Emlid Reach RS2+ base could transmit corrections to the Reach RS3 rover using the inbuilt LoRA radio. However, this would require moving the base to optimal locations – especially with some hilly terrain to the south of town.

As the community still had mobile coverage – and Internet, the simplest solution was to share corrections using the free Emlid Caster service.

Given the project involved a range of locations, the best setup was the middle of town. It had a great skyview, was in the public eye and with reliable Internet. Coincidentally it was less than 100m from the inoperative CORS station.

Caster setup

The base in this case was an Emlid Reach RS2+. The unit has an internal LTE modem allowing it to connect directly to the Internet.

With the base established over a quality known point – the next step was to login to a free Emlid Caster account at https://emlid.com/ntrip-caster/

After logging in, a free mount point configuration will be shown. Enter the mount point credentials into the base settings.

• Go to Reach settings
• Go to Correction output
• Select NTRIP
• Fill in the credentials of your mount point

Setup Rover Credentials

Up to 10 rovers can be connected to a single mount point. Enter the rover credentials into the NTRIP profile on your rovers.

• Go to Reach settings
• Go to Correction input
• Select NTRIP
• Fill in the credentials for your rover