{"id":"19aafc70-9aa7-4783-be6a-5515a6564636","task":"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","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"],"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"],"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/19aafc70-9aa7-4783-be6a-5515a6564636"}