Convert or transform coordinates across datums using the NOAA NGS NCAT web service
domain: geodesy.noaa.gov · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
Choose the sub-service matching your input format: latitude-longitude-height, SPC, UTM, XYZ, or USNG
Submit coordinates plus source/target reference frame (e.g., NAD83(2011), NAD27) and, for heights, source/target geopotential datum (e.g., NAVD88, NGVD29)
NCAT applies NADCON 5.0 for horizontal/ellipsoidal transformations and VERTCON 3.0 for orthometric height transformations
Parse the JSON response, using the metadata endpoint (geodesy.noaa.gov/api/ncat/meta) to interpret returned parameter names
Restrict requests to supported regions (CONUS, Alaska, Hawaii, Puerto Rico/USVI, American Samoa, Guam/CNMI) since NADCON/VERTCON reject out-of-bounds points
Known gotchas
NCAT does not convert between orthometric and ellipsoidal height types — only orthometric-to-orthometric or ellipsoidal-to-ellipsoidal
Valid reference frame/datum options differ by region (e.g., Hawaii uses OHD/NAD83(PA11), not CONUS frames) — passing a CONUS-only datum for a Hawaii point fails
This is a free NOAA government web service with no published SLA or authentication; fine for verification workflows but not guaranteed for high-volume production traffic
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