Data Acquisition

Sidereon.GNSS.Data fetches GNSS archive products and DTED terrain tiles into a verified local cache. It is cache-first, supports offline reads, records provenance next to each data file, and derives product names, URLs, terrain paths, and DTED bytes through the core NIF.

Terrain Quick Start

Fetch the tile first, then pass the terrain cache root to the terrain reader:

{:ok, tile_path} = Sidereon.GNSS.Data.fetch_dted(36.75, -106.25)
terrain_root = tile_path |> Path.dirname() |> Path.dirname()

{:ok, terrain} = Sidereon.Terrain.dted(terrain_root)
{:ok, height_m} = Sidereon.Terrain.height(terrain, -106.25, 36.75)

For fully ocean or no-data tiles, fetch_dted/3 returns:

{:ok, {:no_coverage, tile_id}}

The terrain reader treats absent tiles as sea level, so callers can decide whether to prefetch no-coverage markers or simply rely on the reader fallback.

Bulk Terrain Cache

Populate a region while online:

terrain_root = "/tmp/sidereon-terrain"

{:ok, report} =
  Sidereon.GNSS.Data.prefetch_dted_bbox({36.0, -107.0, 37.0, -106.0},
    cache_dir: terrain_root
  )

report.fetched
report.cached
report.no_coverage
report.errors

Tile lists accept core Skadi ids or {lat_index, lon_index} pairs:

{:ok, report} =
  Sidereon.GNSS.Data.prefetch_dted_tiles(["N36W107", {36, -106}],
    cache_dir: terrain_root
  )

Later, run without network:

{:ok, tile_path} =
  Sidereon.GNSS.Data.fetch_dted(36.75, -106.25,
    cache_dir: terrain_root,
    offline: true
  )

GNSS Products

Build products through the catalog wrappers and fetch them to the GNSS cache:

{:ok, sp3_product} = Sidereon.GNSS.Data.mgex_sp3(:esa, ~D[2020-06-24])
{:ok, sp3_path} = Sidereon.GNSS.Data.fetch(sp3_product)
{:ok, sp3} = Sidereon.GNSS.SP3.load(sp3_path)

{:ok, ionex_path} = Sidereon.GNSS.Data.fetch_ionex(:cod_rap, ~D[2026-06-13])
{:ok, ionex} = Sidereon.GNSS.Ionosphere.load_ionex(ionex_path)

{:ok, nav_product} = Sidereon.GNSS.Data.mgex_nav(:igs, ~D[2020-06-25])
{:ok, nav_path} = Sidereon.GNSS.Data.fetch(nav_product)

{:ok, clk_product} = Sidereon.GNSS.Data.mgex_clk(:gfz, ~D[2020-06-24])
{:ok, clk_path} = Sidereon.GNSS.Data.fetch(clk_product)

Merged SP3 acquisition fetches each contributing center, parses the products, and uses the existing SP3 merge implementation:

{:ok, merged_sp3, report} =
  Sidereon.GNSS.Data.fetch_merged_sp3(~D[2024-09-03], [:igs_ult, :gfz_ult])

Ultra-rapid acquisition probes each center's current primary filename pattern, then known duration/sampling alternates and documented latest-product aliases when an archive returns 404. report.contributors records the pattern that succeeded. Merge policy options are forwarded unchanged, including guarded cell precedence:

{:ok, merged_sp3, report} =
  Sidereon.GNSS.Data.fetch_merged_sp3(
    ~N[2026-07-12 18:30:00],
    [:igs_ult, :cod_ult, :esa_ult, :gfz_ult],
    combine: :precedence,
    min_agree: 1,
    precedence_scope: :cell,
    outlier_reject: [position_m: 0.5, clock_ns: 5.0]
  )

prediction = Sidereon.GNSS.SP3.prediction_summary(merged_sp3)
prediction.observed_through

The default merge timeline uses the finest commensurate input cadence, with lower-precedence centers filling missing cells. No interpolation is introduced. Even one successful contributor passes through the same merge path so system filters and cadence validation remain consistent.

Every fetch returns either {:ok, value} or {:error, reason}. Offline misses, checksum failures, redirects, archive 404s, no-coverage terrain, cache failures, and catalog validation all use typed tagged reasons.