The NGS Geodetic Tool Kit

NGS Geodetic Tool Kit Program Descriptions

on-line interactive computation of geodetic values

DEFLEC99: Computes deflections of the vertical at the surface of the Earth for the conterminous United States, Alaska, Puerto Rico, Virgin Islands, and Hawaii.
DYNAMIC_HT: Computes a dynamic height based on the NAVD88 orthometric height and gravity value.
G99SSS: Computes gravimetric, geocentric geoid undulations relative to the ITRF97/GRS-80 reference ellipsoid in the conterminous United States. Primarily for scientific use.
GEOID99: Computes hybrid geoid undulations, and used to convert between NAD 83 GPS derived ellipsoid heights and NAVD 88 Helmert orthometric heights. Areas covered are the conterminous United States, Hawaii, Alaska and Puerto Rico and the American Virgin Islands.
HTDP: This horizontal time-dependent positioning software program allows users to predict horizontal displacements and/or velocities at locations throughout the United States and its territories. This software also enables users to update geodetic coordinates and/or observations from one date to another.
Inverse/ForwardInvers3D/Forwrd3D: INVERSE is the tool for computing the geodetic azimuth and ellipsoidal distance between two points given their latitudes and longitudes. FORWARD is the tool for computing the geodetic position of a point given the geodetic position of a beginning point and the geodetic azimuth and ellipsoidal distance between the two points. INVERS3D and FORWRD3D are 3-dimensional versions of the above programs.
LVL_DH: LVL_DH Computes the expected leveled difference in height between two North American Vertical Datum of 1988 (NAVD 88) bench marks.
Magnetic Declination: Compute values of Earth's magnetic field, including declination, with a service provided by NOAA's National Geophysical Data Center. Users should be aware that solar storms can cause intense, short-term disturbances in the magnetic field. If there is a major solar storm during a survey, values could be off by as much as 10 degrees! A link to NOAA's Space Environment Center is provided for checking the current space weather forecast.
NADCON: Transforms geographic coordinates between the NAD 27, Old Hawaiian, Puerto Rico, or Alaska Island datums and NAD 83 values. Recommended for converting coordinate data for mapping, low-accuracy surveying, or navigation. PC software is available for download.
NAVD 88 Modelled Gravity: This process is similar to the Surface Gravity Prediction facility in this tool kit, but it uses the model surface developed for the NAVD 88 adjustment rather than current values of the gravity data base. The difference between these two sources of gravity values at a specific point should be no more than a few milligals. NAVD 88 Gravity is the modelled gravity that appears on NGS data sheets.
OnLine Positioning User Service (OPUS): OPUS allows users to submit their GPS data files in RINEX format to NGS, where the data will be processed to determine a position using NGS computers and software. Each RINEX file that is submitted will be processed with respect to the 3 best national CORS sites.
State Plane Coordinates: GPPCGP: Converts NAD 27 State plane coordinates to NAD 27 geographic positions (latitudes and longitudes) and conversely. Includes defining constants for all NAD 27 plane coordinate zones. PC software is available for download.; SPCS83: Converts NAD 83 state plane coordinates to NAD 83 geographic positions and conversely. Includes defining constants for NAD 83 coordinate zones. State plane coordinates are entered or computed to 1 mm accuracy, while the latitudes and longitudes entered or computed correspond to approximately 0.3 mm accuracy. PC software is available for download.
Surface Gravity Prediction: This process is designed to predict surface gravity at specified geographic position and topographic height. The value is determined by interpolation based on observed values. Observed gravity data in the NGS's Integrated Data Base are referenced to an absolute gravity datum.
Tidal and Orthometric Elevations: The tidal information and orthometric elevations of a specific survey control mark can be viewed graphically. Displayed will be the differences between the published NAVD 88 and NGVD29 and Mean Lower Low Water (MLLW) datums.
U.S. National Grid Conversion: Converts between USNG, UTM, and geodetic latitude/longitude. The U.S. National Grid (USNG) System is an alpha-numeric reference system that overlays the UTM coordinate system. It is a Federal Geographic Data Committee (FGDC) standard developed to improve public safety, commerce, as well as aid the casual GPS user. The USNG provides an easy to use geoaddress system for identifying and determining locations with the help of a USNG gridded map and/or a USNG enabled GPS system.; PC software is available for download.
Universal Transverse Mercator Coordinates: The Universal Transverse Mercator Coordinate (UTM) system provides coordinates on a world wide flat grid for easy computation. It divides the World into 60 zones, each being 6 degrees longitude wide, and extending from 80 degrees south latitude to 84 degrees north latitude. The polar regions are excluded. The utilities in this package provide methods for converting between Geodetic Positions and UTM.; PC software is available for download.
VERTCON: Computes the modeled difference in orthometric height between the North American Vertical Datum of 1988 (NAVD 88) and the National Geodetic Vertical Datum of 1929 (NGVD 29) for a given location specified by latitude and longitude. This conversion is sufficient for many mapping purposes.
XYZ Coordinate Conversion: Cartesian Coordinates (XYZ) allow for Geodetic quality three dimensional positioning on an earth centered ellipsoid. The utilities in this package provide methods for converting between Geodetic Latitude-Longitude-Ellipsoid_ht and XYZ on the GRS80 Ellipsoid.

For more information contact NGS Information Services:
by e-mail,
or call (301) 713-3242, Monday - Friday, 7:00 AM - 4:30 PM eastern time.

www.ngs.noaa.gov/TOOLS/program_descriptions.html

updated: April 2, 2002