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Understanding Accuracy
This tool infers distance from signal strength, then trilaterates. Both steps are approximate — knowing why tells you when to trust the fix.
Distance comes from the log-distance path-loss model:
d = d₀ · 10^((PL(d) − PL(d₀)) / (10·n))
d₀ = 1 m reference · n = path-loss exponent · PL = Tx_power − RSSI
It assumes signal decays smoothly with distance. Reality breaks that assumption:
| Assumption | Reality |
|---|---|
| Free propagation | Reflections off buildings, vehicles, ground |
| Single path | Multipath — copies arrive with different phases |
| Static environment | People, doors, cars shift RSSI 5–15 dB |
| Isotropic antenna | The Flipper's PCB antenna is directional |
| Known Tx power | Actual output often differs from nominal |
Multipath is the primary failure mode. A reflection can arrive stronger than the direct path, pushing the estimate in the wrong direction — that's why dense-urban error explodes.
Set it in the drawer to match the environment:
n |
Environment |
|---|---|
| 2.0 | Free space / very open field |
| 2.7 | Suburban |
| 3.0 | Urban (default) |
| 3.5 | Dense urban |
| 4.5–5.0 | Indoor / heavy obstruction |
A wrong n gives systematically biased distances — bad triangulation even with perfect
capture geometry. When in doubt, pick the value that matches what's physically around you.
The solver reports RMS residual in metres — how well the distance circles agree:
- < 30 m — circles agree well, higher confidence.
- 30–100 m — usable as a search area.
- > 100 m — noisy environment or bad geometry; re-capture from better spots.
RMS measures internal consistency, not truth. Low RMS with bad geometry can still be wrong — geometry matters as much as the number (see Field Guide).
- RSSI smoothing — an exponential moving average damps single-sample multipath spikes before a capture is taken.
- Outlier rejection — a leave-one-out residual check flags and excludes captures that look like multipath before the final solve.
- Geometry hint — warns when your captures are too collinear to give an unambiguous fix.
- ❌ Real-time tracking of a moving transmitter
- ❌ Sub-10 m precision in any environment
- ❌ Direction finding (no antenna array)
- ❌ Reliable indoor / room-level localisation
- ❌ A replacement for dedicated DF gear
For the measured numbers, see the Field Validation table in the README.