Lat/Lon ↔ UTM Converter mechanism

Model scope

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.

• 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.

Units and conventions

• 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.

Inspectable vector

One of 4 source-bound review vectors:

{
  "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."
}

Failure boundary

• 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.

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-tranche6/tranche6-results.json