How to Set Up a GPS Base Station for Construction

The GPS base station is the foundation of all RTK accuracy. Every position your rovers collect is relative to the base — if the base is set up wrong, everything is wrong by the same amount. This guide covers the complete base station setup sequence from tripod to transmitting corrections.

Choosing the Base Location

The base location affects rover accuracy, radio range, and reliability. Best base locations: high ground with clear sky view (no buildings or trees within 20 degrees of horizon), central within the rover working area, and secure — not in the path of equipment or traffic. The base needs to stay undisturbed for the full shift. A base that gets bumped mid-shift invalidates all subsequent rover positions until the base is re-established and verified.

For maximum radio range, put the base on the highest available point with clear line of sight to the rover working area. Every meter of additional base elevation adds approximately 5-10km of UHF radio range. On large sites, the base on a hilltop serves the whole site; a base in a depression may not reach the far end.

Setting Up on a Control Point

Set the tripod over your control point — the specific known-coordinate point from which the base will transmit corrections. Use a tribrach with optical or laser plummet to center exactly over the point. Centering error transfers directly to rover positions, so take the time to get it right: centering within 1-2mm is standard practice for construction GPS base setup.

Measure the antenna height carefully. This is a common source of large position errors. The antenna height is measured from the control point to the antenna reference point (ARP) — typically the bottom of the antenna, but check your antenna's documentation. A 10mm error in antenna height = 10mm vertical error on every rover shot. Measure twice, enter once.

Configuring Correction Output

In the base controller (Trimble Access, MAGNET Field, Leica Captivate), enter the base point coordinates, antenna height, and select the correction format. Match the correction format to your rover configuration: if the rover expects RTCM 3.2, the base must transmit RTCM 3.2. Format mismatches are the #1 cause of "I can receive corrections but can't get a fix" problems.

Set the radio transmit interval to 1 second. Set the base altitude to match your project coordinate system — using WGS84 ellipsoidal height when your project is in NAD83 state plane coordinates causes a systematic vertical offset. Configure the base before walking away from it.

Verifying the Base Before Staking

Before staking any design points, verify the base setup by shooting a check shot on a second control point (not the base point itself). The check shot should match the control point's known coordinates within 15-20mm horizontal and 25mm vertical. If the check exceeds tolerance: verify the base point coordinates were entered correctly, verify the antenna height, and confirm the coordinate system is correct. Never start staking without a passing check shot.

Frequently Asked Questions

How do I set up a GPS base station?

Set up a tripod over a known control point, mount the GPS receiver, measure and record the antenna height, enter the control point coordinates into the base controller, configure the correction format to match your rover, and turn on the radio transmitter. Verify with a check shot on a second control point before staking.

How accurate does the base station antenna height measurement need to be?

Measure to ±2mm accuracy. Antenna height errors transfer directly to every rover position — a 10mm antenna height error = 10mm vertical error on all rover shots.

What happens if the base station gets bumped during the day?

If the base moves, all subsequent rover positions may be shifted. Re-verify the base position by shooting a check shot on a known control point. If the check fails, you need to identify which shots were taken before and after the bump.