This is an estimate
We compute where each satellite is from its published orbit (TLE) for your spot and day. We do not know about your trees, buildings, hills or truck. Raise the "hide satellites below" angle to act like a tighter spot. Real-world counts will be lower near obstructions, and signals bouncing off walls (multipath) can still cause trouble when the numbers look good.
What is PDOP?
PDOP (position dilution of precision) measures how well the satellites are spread around the sky. Spread out is good: low PDOP. Bunched up is bad: high PDOP. A common rule of thumb: under 2 is good, 2 to 4 is OK, over 4 is poor. RTK also needs at least 5 satellites. We use those rules to color each hour. Our PDOP treats all systems as one, so it's a little more hopeful than your receiver's.
Data and software
- Orbits: CelesTrak GPS operational, GLONASS operational, Galileo and BeiDou groups, refreshed every 6 hours (with a saved copy as backup).
- Math: satellite.js (MIT license), running in your browser.
- TLE orbits are good to a few miles, which is plenty for counting satellites, but not for precise work.
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