Great-Circle Distance (Haversine) implementation

Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

Record owner

Guth Instruments

Lifecycle

verified-clean

Evidence ID

t4-137

Effect

Computation or source lookup only

Input and validation requirements

• Validate latitude range −90° to 90° and longitude range, typically −180° to 180° or a clearly documented equivalent.
• Floating-point rounding can produce a slightly invalid a outside [0,1]; clamp a to [0,1] before sqrt to avoid NaN.
• The distance formula is safe for coincident points, but initial bearing is undefined for coincident points and antipodal points.
• Initial bearing is numerically unstable or undefined at exact pole configurations and must have documented behavior.
• A spherical distance can differ from an ellipsoidal geodesic distance by roughly up to 0.5% depending on the route; it must not be presented as an exact WGS84 ellipsoidal geodesic.
• If a radius is configurable, reject zero or negative radii.

Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

{
  "inputs": {
    "lat1_deg": 0,
    "lon1_deg": 0,
    "lat2_deg": 0,
    "lon2_deg": 0,
    "radius_km": 6371.0088
  },
  "expected_outputs": {
    "distance_km": 0,
    "initial_bearing_deg": null
  },
  "working": "Δφ=0 and Δλ=0. a=sin²(0/2)+cos(0)·cos(0)·sin²(0/2)=0+1·1·0=0. atan2(√a,√(1−a))=atan2(0,1)=0. d=2·6371.0088·0=0 km. The initial bearing is undefined because the two points coincide."
}

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche4/tranche4-results.json