API for Geoid - The Geoid Height Service

Purpose

This web service distributes the geoid height of the NGS geoid models in a concise and portable way. The web service provides the geoid height (of a model specified by its model ID) at any given latitude and longitude. The primary purpose of the tool is to calculate the geoid height to be used in converting a GNSS derived NAD83 ellipsoidal height into the NAVD88 official orthometric height. This service can be embedded in external websites/software to support other products and services.

Background

The geoid models have been computed in two steps. At the first step, the gravimetric geoid is computed for the United States and its territories including the Conterminous US (CONUS), Alaska, Hawaii, Guam, the Commonwealth of the Northern Mariana Islands, American Samoa, Puerto Rico and the US Virgin Islands. The models are based on a 1′ × 1′ gravity grid derived from the NGS surface gravity data and the altimetry-derived anomalies, the SRTM 3′′ DEM for its topographic reductions, and global satellite geopotential models. At the second step, the gravimetric geoid model is superimposed by the up-to-date GPS data on benchmarks to form so-called geoid using the least squares collocation. The geoid models are designated by GEOIDXX, where XX denotes the two digits year. Since the GPS positions have improved after the latest nationwide adjustment, and since the new satellite gravity models provide an improved gravity field at long wavelengths, the later geoid models are more accurate. Learn more about geoid models.

Metadata

The following URL provides metadata for various parameters used in the JSON response: https://geodesy.noaa.gov/api/geoid/meta

Query Parameter

Description

lat *

Latitude in decimal degrees or degrees-minutes-seconds(DMS) format; if DMS format is used, prefix the value with a hemisphere designator (N or S) and use DDMMSS.ssssss format; decimal seconds are optional.

Example: decimal degrees: 40.75 DMS format N404500.0

lon *

Longitude in decimal degrees or degrees-minutes-seconds(DMS) format; if DMS format is used, prefix the value with a hemisphere designator (E or W) and use DDDMMSS.ssssss format; decimal seconds are optional. For decimal degrees, negative west longitude convention is used.

Example: decimal degrees: -80.75 DMS format W0804500.0

model **

Numeric ID associated with a Geoid model Valid IDs are:

  • 1 = GEOID99
  • 2 = G99SSS
  • 3 = GEOID03
  • 4 = USGG2003
  • 5 = GEOID06
  • 6 = USGG2009
  • 7 = GEOID09
  • 9 = The latest experimental Geoid (XUSHG)
  • 11 = USGG2012
  • 12 = GEOID12A
  • 13 = GEOID12B
  • 14 = GEOID18

defaults to 14, Geoid18, if the parameter is not used

station **
Alphanumeric name associated with a given lat-lon
defaults to UserStation, if the parameter is not used

Example:

https://geodesy.noaa.gov/api/geoid/ght?lat=40.0&lon=W0800000.0
Sample Result Set (Units of Geoid Height and Error are meters):
{
"geoidModel": "GEOID12B",
"station": "UserStation",
"lat": 40.0,
"latDms": "N400000.00000",
"lon": -80.0,
"lonDms": "W0800000.00000",
"geoidHeight": -33.185,
"error": 0.07
}

* Required Field
** Optional Field, to override defaults