GNSS Local Base Settings

Kevin Grover
2025-11-28T19:07:13Z

Whether you are downloading the GNSS corrections yourself from a public network such as CORS, purchasing corrections from a third party, or using your own GNSS equipment as a base station, the workflow with Looq is the same!

Know ahead of your capture if there is a GNSS correction source near your project that will work

Ensure the station you are interested in using is operational and healthy (can be determine from the third party site directly)

If using your own GNSS, ensure the base station is logging data during the entire length of the captures being done

Ensure you know the surveyed location of the station for the Looq processing

CORS / Paid vendors publish this information when downloading the data and usually embeds the position in the header of the RINEX file

When using your own Local GNSS, you will need to know the accurate location of the base station

Setup on a point with published coordinates

Process the base station data to a PPP service (like OPUS or NRCAN) to get its true coordinate

Survey the base point to derive known coordinates

This will be required to be done prior to a Looq capture to ensure all of the proper information is available for post processing.

Critical Requirements for Looq Processing

Regardless of the source, the RINEX file uploaded to the Looq platform must meet these strict criteria to process correctly:

File Format: Must be a RINEX observation file (extensions: .obs, .XXo like .23o).

Minimum Duration: The base file must cover the entire capture plus a buffer.

Rule of Thumb: Start the base 5 minutes before the capture and leave it running for 5 minutes after.

Sampling Rate: 1 Hz (1 second) is the gold standard.

It is possible to process the corrections with a higher interval (15 or 30 seconds), but the results won't be as accurate due to the slower sampling interval when doing a moving capture.

Using a Local Base Station (Recommended for Max Accuracy)

Placement of a local GNSS base station on your site is key to obtain the highest accuracy.

Open Sky: Place the tripod where it has a 360° unobstructed view of the sky. Avoid buildings, tree canopies, and vehicles (multipath interference).

Stability: Use a heavy-duty tripod or secure it to a fixed object. If the base moves even 1cm during recording, your entire dataset shifts by 1cm.

The "Known Point" Protocol:

For Relative Accuracy (measurements within the model are correct): You can set the base up anywhere.

For Absolute Accuracy (model matches the real world/grid): You must place the base on a known survey monument OR process the base's raw file through a PPP service (like OPUS or NRCAN) to get its true coordinate before uploading.

Antenna Height: Measure the height of the antenna from the ground to the center of phase (usually the bumper or specific mark on the receiver). Note this down; you may need to input it or account for it depending on if you are processing for absolute elevation.

Using CORS or Paid Networks (Trimble/Leica)

Both options are ideal with the Looq processing, if there is a base station from a vendor that is close to your project site. Here are some tips to be aware of:

Baseline Distance: Check the distance from your job site to the nearest station before you leave.

< 5 km (3 miles): Excellent accuracy.

5–20 km (3 to 12 miles): Good accuracy (acceptable for most topo/volumetrics).

> 30 km (over 12 miles): Accuracy degrades and may note result in accurate GNSS corrections.

Downloading the Data:

Log into the provider's portal (e.g., NOAA NGS, SmartNet User Portal).

Select the "Reference Station" closest to your site.

Select the time window (UTC time). Crucial: Convert your local flight time to UTC to ensure you download the correct hours.

Download the RINEX v3.0 (preferred) or v2.11 format.