History


What is VERTCON 3.0?

NGS's Vertical Datum Conversion Utility (VERTCON) tool helped users transform orthometric heights between a few specified datums, but that tool had limitations. It was poorly documented and only supported one pair of datums in one region of the United States.

VERTCON 3.0 was a project whose intent was to create new “build software”, and use that software to build and release new transformation grids both replacing earlier VERTCON transformation grids and creating some new transformations as well. These new transformation grids, as well as the VERTCON 3.0 build software were packaged and released to the public as “VERTCON 3.0 release 20190601”.

VERTCON 3.0 is not a stand-alone product, like previous versions of VERTCON. Rather it is the name of the project and the name of the “build software” created within that project. Once the build software was complete, it was used to generate grids as part of VERTCON 3.0 release 20190601. However, the actual functionality of using those grids is encoded in the NGS Coordinate Conversion and Transformation Tool (NCAT).

Other improvements include:

  • consistent and well-documented methods;
  • user-friendly access through the NGS Coordinate Conversion and Transformation Tool; and
  • downloadable transformation grids that can be integrated into third-party software.

In addition, an effort was made to maintain consistency of physical models used in VERTCON 2.0/2.1, while also respecting large regional changes in NAVD 88 heights which have occurred since the original 1991 release of NAVD 88.

More specifically, VERTCON 3.0 release 20190601 supports transformations between all chronologically paired vertical datums of the National Spatial Reference System, dating back to the 1920’s. Unlike previous transformation tools, VERTCON 3.0 provides local error estimates for each transformation grid.

VERTCON 3.0 release 20190601 contains high resolution grids used in NCAT to obtain unprecedented exactness in modeling coordinate differences. While reported transformation quality is extremely good, it is not comparable to a geodetic readjustment of survey measurements. NGS considers readjustment of survey measurements as best practice, rather than coordinate transformations.

How can I learn more about VERTCON 3.0?

NOAA Technical Report NOS NGS 68 (PDF, 17 MB) provides detailed information on VERTCON 3.0 and a digital archive includes additional plots and data. The report:

  • discusses the scientific approach used for the transformations;
  • provides plots and discussion for each transformation and its errors; and
  • details the history of datum transformations and coordinate transformation tools at NGS.