Waymark / Routes / epqs.nationalmap.gov Query a single-point ground elevation from USGS 3DEP via the Elevation Point Query Service (EPQS) for spot-check QA of survey-grade GNSS heights
domain: epqs.nationalmap.gov · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checked community attestations: 0✓ / 0✗
Steps Build a GET request to epqs.nationalmap.gov/v1/json?x=<lon>&y=<lat>&units=Meters&wkid=4326 Confirm the response includes the interpolated elevation and the source resolution used (1m lidar where available, else 1/3 arc-second) Compare the returned elevation against your field-observed geoid-converted orthometric height as an independent QA check For multiple points, loop the request per coordinate; there is no documented bulk/batch endpoint on this service Review the accuracy caveat (roughly 0.53m RMSE nationally, varies locally) before using this as anything beyond a sanity check Known gotchas Coordinates outside CONUS/AK/HI/territory 3DEP coverage return no data or a lower-resolution fallback without a clear warning This is an interpolated raster query, not surveyed elevation — never substitute it for GNSS/leveling control on a legal survey Full docs live at epqs.nationalmap.gov/v1/docs; parameters differ from the older TNM elevation service, don't reuse old query strings
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