Scenario kind pagesEdit on GitHubSource: docs/kinds/by-kind/combined-altpnt.md

combined-altpnt (scenario kind)

Scenario kind of the engine v0.38.0, family GPS-denied alternative PNT. Advisory: analysis output from a research and engineering tool, not type-approved navigation equipment and not a safety-of-life service. Every label here is the engine's or the verification matrix's; a kind is MODELLED unless the matrix says otherwise (how a label is earned: the README's Evidence section).

What it does#

GPS-denied combined gravity + magnetic + terrain navigator: three scalar field channels fused per waypoint for a sharper (lower-CRLB) drift fix than any single field.

One run of scenarios/combined-altpnt.toml summarises as: combined-altpnt | free-inertial drift 70659 m | gravity 464 m magnetic 782 m terrain 368 m | FUSED 365 m

Inputs#

From the schema (kshana kinds --json):

  • Required fields: start_lat_deg, start_lon_deg, step_lat_deg, step_lon_deg, waypoints, drift_lat_deg, drift_lon_deg, search_half_deg, search_step_deg, nmax, gravity_sigma_mgal, igrf_year, magnetic_sigma_nt, dem_seed, terrain_sigma_m
  • Optional fields: coeffs, mascons, magnetic_mascons, igrf_alt_km, refine_stages, refine_factor, noise_seed, magnetic_grid

The example scenarios/combined-altpnt.toml sets, among others:

Field Value Unit
coeffs[0].cbar 6.0000e-6 not stated
coeffs[0].m 0 not stated
coeffs[0].n 2 not stated
coeffs[0].sbar 0 not stated
coeffs[1].cbar 3.0000e-6 not stated
coeffs[1].m 1 not stated
coeffs[1].n 3 not stated
coeffs[1].sbar 2.0000e-6 not stated
dem_seed 1 not stated
drift_lat_deg 0.5 deg
drift_lon_deg -0.4 deg
gravity_sigma_mgal 3 mGal

Run it#

kshana scenarios/combined-altpnt.toml

What it gives#

The scalar results of that run, with the units the engine states:

Result Value Unit
combined_m 364.881333 m
free_inertial_drift_m 70658.643788 m
gravity_only_m 464.136358 m
magnetic_only_m 782.430009 m
terrain_only_m 367.623242 m
The chart the engine writes for scenarios/combined-altpnt.toml, kind combined-altpnt

Evidence#

No matrix row names this kind by name; the label on its result is the engine's own, above.

The rows the run itself exercised, with the oracle the matrix gives each (the public sources are named there):

  • MODELLED Gravity-map matching, terrain-referenced (TERCOM/SITAN), magnetic anomaly. Oracle (InternalConsistency): IGRF-14 coefficients; first-principles matched-filter CRLB. The real-field gravity benchmark's field is externally checked (row 'Gravity-anomaly synthesis from a spherical-harmonic model'), but its navigation outcome has no external oracle
  • MODELLED Deterministic, scenario-hashed, SBOM + cross-platform golden gates. Oracle (ExternalDataset): SBOM conformance to the official CycloneDX 1.5 JSON Schema (+ valid SPDX identifiers) — an external published standard, zero validation errors over the full dependency graph; the FoM-determinism / byte-reproducibility part remains a pinned self-consistency check, so the row stays MODELLED

Limitations#

What the run's own report says is not modelled or not validated:

  • Alternative / complementary PNT is MODELLED, not validated: checked against its own closed-form / analytic identity — catches transcription and coefficient errors, but is not an external oracle. (verification matrix (docs/MODELLED-RATIONALE.md))
  • Reproducibility & software assurance is MODELLED, not validated: a sub-claim is externally checked, but the whole capability composes modelled pieces, so the capability stays Modelled. (verification matrix (docs/MODELLED-RATIONALE.md))

See also#