Saying Goodbye: The Vanishing Reality of NAD83 and NAVD88
I recently attended the National Geodetic Survey’s (NGS) workshop on the future of the horizontal and vertical datums. Industry leaders and software companies gathered with NGS representatives to discuss the logistics and implications of migrating to new datums.
Since the 1980s, the United States and some North American neighbors have used the North American Datum of 1983 (NAD83) and the North American Vertical Datum of 1988 (NAVD88) for horizontal and vertical georeferencing (respectively). Pre-GPS, both datums were designed and published before satellites were routinely used to determine earth shape and position, such as latitude and longitude.
NAD83 is a static datum, meaning that coordinates are fixed. However, because earth’s tectonic plates are constantly moving, changing location values render these fixed coordinates inaccurate.
Advancements in technology have also highlighted the inaccuracies of NAD83 and NAVD88. For example, space-based technologies and 3D positioning techniques have proven that NAD83 is off-center by as much as two meters. NAD83 is not the truly geocentric system that the International Terrestrial Reference System (ITRF) or World Geodetic System of 1983 (WGS83) is.
Through the National Spatial Reference System modernization program, which is expected to be completed during 2022, NAD83 is expected to be replaced with the following datums:
- North American Terrestrial Reference Frame of 2022 (NATRF2022)
- Pacific Terrestrial Reference Frame of 2022 (PATRF2022)
- Caribbean Terrestrial Reference Frame of 2022 (CATRF2022)
- Mariana Reference Frame of 2022 (MATRF2022)
Named for each of the four tectonic plates, each reference frame will rotate with its respective plate.
For vertical reference, NGS will replace NAVD88 with a consistent geopotential datum called the North American-Pacific Geopotential Datum of 2022 (NAPGD2022). Built upon the International GPS Service (IGS) frame, NAPGD2022 will operate equally well in any of four new horizontal reference frames. NAPGD2022 orthometric heights will primarily be accessed through Global Navigation Satellite System (GNSS) technology and defined through ellipsoid heights and the new gravity-based GEOID2022.
So, what’s next?
Around the year 2020, we will begin realigning our locations and positions with the world’s most accurate reference frames, ITRF and International GNSS Service, in a move reminiscent of the DoD’s switch to the World Geodetic System of 1984 (WGS84).
With this new GPS compatibility, we can expect better 3D positional accuracy. Dynamic survey positions will be updated over time to more accurately reflect the physical positions of specific locations on earth’s continuously shifting surface.
Sounds great. But what about the challenges this modernization program may present?
- There will no longer be a single coordinate for a single point on earth. Because surveyed coordinates will be time-dependent, over time, surveyed positions will become obsolete if they are not updated to reflect actual tectonic movement. Although the change itself will be small, future surveys of identical locations will produce different coordinate values.
- All existing maps and geospatial data referenced to NAD83 will be centered approximately two meters off the new reference frames (unless converted to the new reference frames). We currently manage a vast volume of geospatial data, and a conversion effort would be massive.
- Our technology toolbox may need to be either updated or completely rewritten to accommodate the new reference frames. Conscientious software companies will quickly implement such changes into their products.
- We will need to train our workforce, including not only technical but also sales and marketing staff, on the reality and applications of the new reference frames.
- We will need to educate clients and data users on the forthcoming changes to help them better understand the changes that affect their contracts and deliverable specifications.
Kudos to NGS for taking this giant leap during such an exciting time of rapidly advancing space-age surveying technology.