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.
Great job , wish you and your team all the best.
Albeit I agree on an exciting time but given the excitement I believe this migration to a new datum will unfortunately create a greater chaos. Especially with the Land Information Managers and getting their heads wrapped around how to manage this new datum/system. The ever changing positioning of the control network and the role it serves for the cadastral layer with regards to lengths and bearings, FEMA flood plain mapping, or even geospatial base data (i.e., orthoimagery) will ultimately create cost increases to their strapped budgets and possibly create confusion on their relationship to previous programs. These changes are tremendous and education is definitely part of it but it really boils down to educating the educators who need to start teaching so future GIS technicians and mapping scientists understand the role they will need to play in how this new system will work with their current data layers. The scientific world looks at new systems because they can, however, I think managers of geospatial data sets/layers need to really understand the significance before they look to move to this new system. You can look outside of the United States and find systems that separately support land management and another used by scientist and/or military. They both have a specific roles and both work quite well. Unfortunately, our current society tends to jump to something new because we can but we really must ask the question, does this really make sense? What role does it play and overall what ROI will this change provide going forward with this new datum?
Furthermore, having no real firm positions to reference digital base data is also a slippery slope especially given how metadata is typically poorly populated and/or not even completed which further complicates matter when one is trying to relate existing data to this new system or even when we look down the road and collect ortho imagery in 2040 or even 2050 for say a census year. Given that less than 30 years ago that the two systems were considered one-in-the-same and now today we are off over 2 meters (3D sense). This difference would exceed any large scale mapping tolerances and would create systematic errors if not properly referenced/shifted to the appropriate time in which the geospatial data was collected and referenced to data sets collected today. Personally, having it referenced and fixed to the North American plate (i.e. NAD83) which allows 95% (west coast being the exception) of the United States a stable platform for most geospatial data to be related on and more importantly a system that is fixed and serving municipalities, communities, counties, state, and federal agencies very well (in my opinion) makes it somewhat difficult in jumping to this new datum.
We understand that the earth is constantly moving given plate tectonics and glacier rebounding but this matter is really at a scientific and/or military level. Not at a local interest or even a state level interest. The existing base data that has been collected over the last 30 years has a greater significance that should not be ignored and to adjust/convert based on a newer datum that is considered 3D seems to be a bit overreaching since GPS technologies has been able to relate to the 2D – NAD83 and 1D – NAVD88 very well even though one might say it has been fraught with “some” inaccuracy. The current system (CORS network along with VRS capabilities) seem to be working well given we continue to see new systems coming online each day.
I don’t mean to come across harsh but I think we need to be less excited and be more diligent and practical with proper planning in place with a more in depth understanding of the tangible benefits before making the jump.
Great write-up but I think we need more information prior to migrating to this new datum.
Wow, great article.