Source: https://guthlabs.ai/docs/instruments/haversine-sunrise-azimuth-bearing-great-circle-course/implementation/

instrument implementation / implementation-contract

# Haversine Sunrise-Azimuth Bearing (great circle course) implementation

A source-bound implementation contract for Haversine Sunrise-Azimuth Bearing (great circle course); deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## 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**: t5-109

**Effect**: Computation or source lookup only

## Input and validation requirements

Coincident points produce atan2(0,0), so both bearings are undefined and must be rejected. The specification also leaves longitude sign, angular units, bearing normalization, and the final-bearing derivation implicit, creating convention-dependent outputs if those conventions are not fixed.

## 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": 0,
    "lon1": 0,
    "lat2": 0,
    "lon2": 90,
    "coordinate_units": "degrees"
  },
  "expected_outputs": {
    "initial_bearing_deg": 90,
    "final_bearing_deg": 90
  },
  "working": "Δλ=90°=π/2; φ1=φ2=0°=0 rad. y=sin(π/2)·cos(0)=1·1=1. x=cos(0)·sin(0)−sin(0)·cos(0)·cos(π/2)=0−0=0. θ=atan2(1,0)=π/2=90°. For the final bearing, reverse the route: bearing(0°,90°→0°,0°)=270°, then (270°+180°) mod 360°=90°."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/haversine-sunrise-azimuth-bearing-great-circle-course/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/haversine-sunrise-azimuth-bearing-great-circle-course/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/haversine-sunrise-azimuth-bearing-great-circle-course/qualification/>)

## Sources and evidence

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

- `VERIFIED_LEDGER.json`

- `evidence-tranche5/tranche5-results.json`