🛰️ GPS Trilateration

Satellites 4 Range noise σ (m) 8 Receiver clock bias (m) 0 Geometry preset

Ideal 4-sat

Clustered (high GDOP)

Noisy urban

Clock-bias demo

Satellite Range circle True position Estimate Error ellipse

Estimate (m)—

Position error—

GDOP—

Clock bias est.—

RMS residual—

Each satellite gives a range r = c·Δt — a circle of possible positions. Three circles intersect at one point in 2D; a 4th unknown (receiver clock bias) needs one more satellite. With noise the circles miss, so we solve a least-squares fix and report the error ellipse. GDOP (geometric dilution of precision) blows up when satellites cluster together. Drag any satellite to change the geometry.