Fixed vs. Float in RTK GNSS — What’s the Difference and Why It Matters
If you’re using an RTK GNSS system, you’ve likely seen two status indicators during your survey work: FIXED and FLOAT. But what do they really mean? And why should you care?
This article breaks down the difference between FIXED and FLOAT RTK status, what affects it, and how to keep your GNSS system locked on FIXED.
📌 What Is RTK?
RTK (Real-Time Kinematic) is a satellite positioning technique that allows centimeter-level precision using correction data from a nearby base station.
In this system, your rover (moving unit) receives data from both satellites and a base. Your GNSS receiver then calculates a corrected position. But depending on signal quality, you’ll get either a FIXED or FLOAT solution.
✅ What Is FIXED?
FIXED means the receiver has confidently resolved the phase ambiguity of satellite signals. Your measurements are precise, typically within:
- ✔️ 1–2 cm horizontally
- ✔️ 2–3 cm vertically
This is the ideal state. It’s the reason you bought RTK gear.
⚠️ What Is FLOAT?
FLOAT means the receiver hasn’t fully solved the ambiguity. You’re still getting corrections, but the accuracy may range between:
- ➖ 10–50 cm horizontal error
- ➖ Up to 1 meter vertical error
FLOAT is unstable and not suitable for high-precision survey tasks.
📉 What Causes FLOAT RTK Status?
- 📶 Poor signal between base and rover
- 🌳 Obstructions like trees, buildings, or vehicles
- 📡 Weak satellite geometry (low DOP)
- 🔋 Low battery or overheating receiver
- 📡 Interference from radio towers or high-voltage lines
- 🚧 Improper base setup or incorrect antenna height
Even a few seconds of signal drop can force your FIXED status to revert to FLOAT.
🛠️ Tips to Maintain FIXED RTK
- 🔋 Keep base and rover fully charged
- 📶 Maintain line of sight between antenna and sky
- 📍 Place base on firm, known location
- 🔢 Use GNSS units that support multi-constellation (GPS + GLONASS + Galileo + BeiDou)
- 📱 Use a reliable NTRIP correction source if using CORS
Many surveyors forget that FLOAT can still look good — but lead to positional drift. Always wait for FIX before capturing critical points.
📊 Real-World Example
You’re surveying a boundary line in a suburban area. Your receiver reads FLOAT due to a nearby metal fence and tree cover. You mark a corner at FLOAT, thinking it’s “close enough.”
Later, the same point recorded at FIX is 30 cm off — and your boundary stake is now in your neighbor’s yard. 😬
Moral: Always wait for FIX!
🔍 FIX Quality Checklist
- ✔️ FIXED solution status shown in app
- ✔️ PDOP under 2.0
- ✔️ RMS error under 0.03m
- ✔️ Stable values across multiple epochs
🙋 Final Thoughts
Understanding the difference between FIXED and FLOAT RTK isn’t just technical trivia — it’s essential for professional, defendable survey results. Always strive for FIX, and if you’re stuck in FLOAT, investigate the cause before continuing.
🧰 Need Help Troubleshooting RTK?
We help surveyors identify and solve FIX issues with used GNSS receivers, NTRIP setups, and antenna placement. Contact us for free consultation or browse ready-to-use RTK kits.
Next article: “How to Use a GNSS Receiver with FieldGenius for Android”