tofdr

Beacon ranging simulation with a web UI. A client moves at a set speed and bearing while fixed beacons measure their distance to it with uniform noise. The client periodically multilaterates its position from the latest range estimates (least-squares Gauss-Newton, minimum 4 beacons) and reports a 1-sigma position uncertainty. The web app shows the real and estimated client, track histories, and an uncertainty bubble on a top-down map.

Setup

Requires Python 3.10+.

source .venv/bin/activate
pip install -e ".[dev]"

Running the web app

python -m tofdr.webapp

Then open http://localhost:8000 (served on 127.0.0.1 only). The simulation runs server-side; the browser steps it at ~10 Hz and redraws the map.

Using the UI

Simulation panel (each change restarts the world):

Control	Meaning	Default
beacon estimate rate	how often each beacon produces a range estimate (Hz, fractional)	2
client report rate	how often the client computes a position fix (Hz; may exceed the beacon rate)	5
client speed	real client speed (m/s)	1.5
client direction	bearing in degrees clockwise from north	90
ranging noise	uniform noise added to each beacon's distance (± m)	5

Beacons panel:

• Number of beacons (1-32); new beacons are placed on a ring of radius 200 m around the start point. Position estimation needs at least 4 beacons — otherwise a warning is shown and no estimate is drawn.
• Each beacon's x (east), y (north), and altitude (meters above ground) can be edited in the table, or the beacon can be dragged directly on the map. Altitude spread matters: a couple of high beacons give the solver vertical information.

Map and readout:

• Green dot: real client; gray line: true track.
• Orange dot: estimated client; dashed orange line: estimate track; filled bubble: 2-sigma horizontal uncertainty, outline: 1-sigma.
• Blue squares: beacons (labeled b1, b2, ...).
• Readout above the map shows the current horizontal error, sigma horizontal, sigma vertical, and the rate configuration.
• The view auto-fits and only expands; it recenters on the next config change.
• Pause/Resume freezes the simulation; Reset restarts with the current settings.

HTTP API

The UI is a static page over a small JSON API:

• GET /api/state — current world state (beacons, true/estimated position, tracks, error, config).
• POST /api/config — replace the world. Body: {"beacons": [{"x", "y", "alt"}, ...], "beacon_rate", "report_rate", "speed", "bearing", "noise"}; omitting beacons uses n_beacons on the default ring. Invalid values fall back to defaults.
• POST /api/step — advance the world by {"dt": seconds} (capped at 5 s) and return the new state.

Tests

pytest