Convert NAD83 GNSS ellipsoidal heights to NAVD88 orthometric heights using the NOAA NGS Geoid Height Service API

domain: geodesy.noaa.gov · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗

Steps

  1. Determine which geoid model your project datum requires (GEOID18 is default, model=14; earlier models use IDs 1-13)
  2. Call geodesy.noaa.gov/api/geoid?lat=<DD>&lon=<DD>&model=14
  3. Read the geoid height value from the JSON response
  4. Combine the geoid height with the GNSS-derived ellipsoid height per the sign convention documented at geodesy.noaa.gov/GEOID/ to get NAVD88 orthometric elevation
  5. Batch process multiple bench marks by looping the same call across a point list, pacing requests to avoid hammering the server

Known gotchas

Related routes

Programmatically convert a set of NAD83 GPS-derived coordinates into State Plane Coordinates and NAVD88 orthometric heights using NGS's transformation engine.
geodesy.noaa.gov/web_services/ncat · 5 steps · unrated
Compute the NAVD88 geoid separation for a GNSS-derived ellipsoid height at a specific project point.
geodesy.noaa.gov/web_services/geoid.shtml · 5 steps · unrated
Apply the current NGS hybrid geoid model in GNSS workflows
geodesy.noaa.gov · 5 steps · unrated

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