VDatum Free Software - Convert Horizontal, Vertical Datums

Posted by GIS talk On Sunday, October 23, 2011
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VDatum is a free software tool being developed jointly by NOAA's National Geodetic Survey (NGS), Office of Coast Survey (OCS), and Center for Operational Oceanographic Products and Services (CO-OPS). VDatum is designed to vertically transform geospatial data among a variety of tidal, orthometric and ellipsoidal vertical datums - allowing users to convert their data from different horizontal / vertical references into a common system and enabling the fusion of diverse geospatial data in desired reference levels.

VDatum converts the following:

1. Horizontal datums: from NAD 27 or NAD 83(1986) to NAD 83(HARN) and other ellisoidal datums such as WGS 84 and ITRF

2. Vertical datums: among three vertical groups: tidal datums, orthometric datums and ellipsoidal datums (i.e. three-dimension or 3-D datums), in which:

- Tidal datums are available along the coastlines from Rhode Islands to Texas and from Washington to California. (Why doesn't VDatum provide tidal conversions inland?)
- Transforms among ellipsoidal and orthometric datums are available throughout the United States;
- Conversions between the NAD 83 ellipsoidal datum and the NAVD 88 orthometric datum are calculated base on the current GEOID model of 2009. Previous NGS's GEOID models are also supported, including GEOID 99, GEOID 03, GEOID 06 ;
- Conversions between the NGVD 29 datum and the NAVD 88 datum are done by the NGS's VERTCON model;
- Conversions between IGLD 85 datum and the NAVD 88 datum in the Great Lakes are done by the NGS's IGLD85 model;

3. Input elevation data in geographic (latitude, longitude), UTM (northing, easting) and geocentric XYZ coordinates.

VDatum was first introduced to support a seamless bathymetric - topographic digital elevation model (DEM) for Florida's Tampa Bay region by merging the "best available" NOAA bathymetric data and USGS topography data. The best available bathymetric data were selected from the NOAA / NOS Hydrographic Survey database. For the Tampa bay region, approximately half of the sounding data collected were referenced to a mean low water (MLW) vertical datum, and the other half to a mean lower low water (MLLW) vertical datum. The best available topographic data were selected from the USGS National Elevation Dataset (NED). The NED dataset is horizontally referenced to NAD 83 and vertically referenced to NAVD 88. Prior to merging, both dataset were transformed to a common reference coordinate system, both horizontally and vertically, using VDatum.

The seamless bathy-topo DEM resulting from the VDatum Demonstration Project in Tampa Bay has not only proved to solve the problem of inconsistency among diverse dataset of bathymetry, topography and shorelines data that causes difficulty in mapping coastal regions, but also provides standard geospatial data for multiple applications. Applications benefiting from VDatum include:

- Inundation modeling: storm surge, tsunami, sea level rise impacts
- Ecosystem modeling and coastal managements
- Hydrographic survey depths using Kinematic GPS for vertical referencing
- Shoreline extraction from LiDAR data

Download the free VDatum software here.


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