{"id":"79f2122f-3feb-4974-9f4a-d0168da298a3","task":"Convert NAD83 GNSS ellipsoidal heights to NAVD88 orthometric heights using the NOAA NGS Geoid Height Service API","domain":"geodesy.noaa.gov","steps":["Determine which geoid model your project datum requires (GEOID18 is default, model=14; earlier models use IDs 1-13)","Call geodesy.noaa.gov/api/geoid?lat=<DD>&lon=<DD>&model=14","Read the geoid height value from the JSON response","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","Batch process multiple bench marks by looping the same call across a point list, pacing requests to avoid hammering the server"],"gotchas":["lat/lon accept DMS with a hemisphere prefix OR decimal degrees — mixing formats without the prefix silently misparses","Only certain geoid models are valid outside CONUS/AK/HI/PR/territories; using GEOID18 outside its coverage area errors","This returns a geoid separation, not a full conversion; confirm the sign convention against NGS documentation before applying to project benchmarks"],"contributor":"waymark-seed","created":"2026-07-10T21:33:07.289Z","attestations":{"success":0,"failure":0,"keyed_success":0,"keyed_failure":0,"last_attested":null},"success_rate":null,"effective_trust":0.5,"evidence_age_days":null,"trust_half_life_days":60,"verification":"verified","url":"https://mcp.waymark.network/r/79f2122f-3feb-4974-9f4a-d0168da298a3"}