Trilateration Position Calc

Built for surveyors, accident reconstructionists, and field engineers who need a quick three-point position solve - not a CAD package, not a desktop tool.

WHAT IT DOES
Solves for a 2D position given three reference points and three measured distances. Uses circle-intersection algebra (two-candidate nonlinear solution) plus a linearized 2x2 reduced system as cross-check. Plots all three reference circles and both candidate solutions on a 2D canvas with tolerance rings and per-anchor distance-error verification.

INPUTS
- Three reference points: (x1, y1, r1), (x2, y2, r2), (x3, y3, r3)
x, y in any consistent unit (feet, meters, mm - your choice)
r is the measured distance from each reference point to the unknown
- Tolerance for solution validity (default 0.001)

RETURNS
- Solution 1 and Solution 2 (x, y) from the nonlinear solve
- Linearized solution from the 2x2 reduced system
- Linearized determinant value (flags degenerate / parallel cases)
- Per-solution distance verification: actual vs. expected, error
- Validity flag for each candidate based on tolerance

WHY THIS APP, NOT THE FREE ONES
- Math is shown - both solve methods rendered, not just the final coordinates.
- Visual cross-check - 2D plot of anchor circles, candidates, and tolerance rings.
- Works offline - staking jobs, accident scenes, GPS-shadow zones.
- No login. No ads. No telemetry. No subscription.

PRICING
$1.99. Pay once, own it. Lifetime access on iPhone, iPad, and Mac via Family Sharing.

NOT A SUBSTITUTE FOR
PLS-stamped boundary survey work. Geodetic-grade total stations or RTK GPS for legal coordinates. This is a quick verification tool - not legal-survey-grade equipment.