Particle filter playground

Turn GPS off, add noise, and watch a particle filter keep track of a vehicle crossing hilly terrain. Everything runs in your browser.

LIVE DEMO · PARTICLE FILTER

GNSS UNAVAILABLE

Contour map of terrain with a dashed flight track and clouds of particles that start widely spread, tighten at each update and converge at the end, with a profile chart below comparing terrain height with radar altitude minus barometric altitude.
  • true route
  • estimate
  • particles

Illustrative

CONTROLS

500
Medium
1×
POSITION ERROR
± 12 m
HEADING
040°
EFFECTIVE PARTICLES
312 / 500

Simulated, with illustrative synthetic terrain. Runs locally; nothing is sent anywhere.

Assumptions behind the figures
  • The terrain is a made-up height field, not real elevation data
  • The robot measures the height under it with noise, and its own motion with a small error
  • With GNSS on, a noisy position fix is also used
  • Particles are resampled (systematic resampling) when the effective number drops below half

HOW IT WORKS

Three steps, repeated many times a second

  1. Predict

    Move every particle using the vehicle’s speed and heading, plus a little random noise.

  2. Weight

    Compare each particle with the latest measurement. Particles that agree get more weight.

  3. Resample

    Keep the likely particles, drop the unlikely ones. The cloud closes on the truth.

TRY THIS

Things to try

  • Turn GNSS off and watch the cloud spread out
  • Drop to 50 particles and see the filter lose track
  • Increase sensor noise and compare the heading error
  • Hide the true route and guess where the vehicle went

MORE

Other demos

LIVE DEMO

Spot the spoof

Watch a position get dragged away, and which checks catch it.