Source: https://guthlabs.ai/docs/instruments/lat-lon-utm-converter/

instrument / verified-with-binding-errata

# Lat/Lon ↔ UTM Converter

The current ledger marks this instrument verified with errata that must be applied at binding time.

Status: **VERIFIED_WITH_ERRATA**Lifecycle: **verified-with-binding-errata**

## Inspectable records

[01**Overview**Purpose and lifecycle](<https://guthlabs.ai/docs/instruments/lat-lon-utm-converter/>)[02**Mechanism**Method and assumptions](<https://guthlabs.ai/docs/instruments/lat-lon-utm-converter/mechanism/>)[03**Implementation**Binding and validation](<https://guthlabs.ai/docs/instruments/lat-lon-utm-converter/implementation/>)[04**Qualification**Evidence and errata](<https://guthlabs.ai/docs/instruments/lat-lon-utm-converter/qualification/>)

## Ledger state

The current ledger marks this instrument verified with errata that must be applied at binding time.

**Area**: Earth & Space (astronomy, orbital mechanics, meteorology, geology, geodesy, oceanography)

**Tranche**: tranche-6

**Evidence ID**: t6-060

**Ledger rows**: 1

No ledger note is attached.

## Review findings

The projection family is standard and suitable for the claimed conversion, but the specification is not complete enough to verify one deterministic implementation. Require an explicit WGS84 datum, forward/inverse equations and series order, zone-selection rules, hemisphere encoding, valid latitude range, longitude normalization, and accuracy/rounding guarantees before marking PASS.

### Formula and scope findings

- The stated Transverse Mercator (Karney/USGS series) method is appropriate, but no actual forward or inverse equations, series order, or truncation/error tolerance are specified.

- The datum is not explicitly bound to WGS84 in the computation definition, although WGS84 constants are listed as a data need; results must state the ellipsoid/datum.

- Automatic zone selection is underspecified, including longitude-zone boundaries, longitude 180 degrees, and the Norway and Svalbard UTM exceptions.

- The inverse input must explicitly include hemisphere or a signed/encoded false northing convention; zone, easting, and northing alone are ambiguous between northern and southern UTM.

- UTM is not valid globally near the poles; the honest label correctly mentions UPS, but the accepted latitude range and validation behavior are not specified.

### Unit assumptions

- Latitude and longitude inputs are geodetic degrees; longitude is positive east and latitude is positive north.

- UTM easting and northing outputs and inputs are metres.

- Calculations below use the WGS84 ellipsoid: a = 6378137 m, inverse flattening = 298.257223563, e² = 0.00669437999014, and scale factor k0 = 0.9996.

- UTM uses a 500000 m false easting; northern-hemisphere false northing is 0 m and southern-hemisphere false northing is 10000000 m.

- The examples use the standard USGS high-order series, with results rounded to the shown decimal places.

## Boundary hardening

### Recorded hazards

- Reject or route latitudes outside approximately 80 degrees south to 84 degrees north to UPS; do not silently return ordinary UTM coordinates near the poles.

- Validate longitude range and define normalization, especially longitude 180 degrees and values outside [-180,180].

- Zone must be an integer from 1 through 60; inverse conversion also requires an explicit hemisphere.

- Do not confuse UTM false northing with signed northing. Southern UTM northings near the equator are close to 10000000 m.

- Central-meridian and zone-boundary behavior needs a documented convention; the Norway and Svalbard special zones must be implemented if automatic zone selection is claimed.

- Floating-point precision and series order affect sub-metre results; the instrument should expose or document its accuracy and rounding policy.

- A malformed zone, hemisphere, latitude, longitude, easting, or northing should produce a validation error rather than a plausible-looking coordinate.

## Errata and corrections

### Tranche errata

**northing_m** · vector 3

5411943.794

5411932.678

hand-evaluated TM series slip (~11 m); my series verified exactly on v1/v2

**northing_m** · vector 4

6347211.686

6348713.056

1.5 km error in the southern-hemisphere northing; numeric meridian-arc integral gives 3,652,748.04 m for 33 deg -> N = 1e7 - 0.9996*M = 6,348,713.06

## Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

````
{
  "inputs": {
    "direction": "forward",
    "latitude_deg": 0,
    "longitude_deg": 3,
    "zone": 31,
    "hemisphere": "N",
    "datum": "WGS84"
  },
  "expected_outputs": {
    "zone": 31,
    "hemisphere": "N",
    "easting_m": 500000,
    "northing_m": 0
  },
  "working": "Zone 31 central meridian = 6(31) - 183 = 3 degrees. Therefore longitude difference dlon = 3 - 3 = 0 degrees. At latitude phi = 0, meridional arc M = 0, and every transverse-Mercator correction containing dlon is 0. E = 500000 + k0*(0) = 500000 m. N = k0*M = 0 m."
}
````

## Related workflows

No source-defined multi-instrument workflow membership is recorded.

## Sources and evidence

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

- `VERIFIED_LEDGER.json · VERIFIED_WITH_ERRATA`

- `evidence-tranche6/tranche6-results.json`