Spatial reference system updates

At the Canadian Geodetic Survey (CGS), we maintain and update the standards you use to reference positions (latitude, longitude and height) and gravity in Canada.

Our published coordinates and gravity values may change with updates to the reference system or the reference frame. They also change in time, either from sudden events that have a dramatic impact (e.g., earthquakes, landslides) or long-term events that are not very noticeable (e.g., tectonic plate motion and glacial isostatic adjustment). We identify the reference frame version and coordinate epoch in all metadata so you know which reference system, reference frame and epoch they’re from.

The sections below outline the current reference systems, frames and epochs adopted by the CGS and the provinces. They also provide an overview of the current modernization project underway in the U.S. and how it will impact Canada.

 

Updates to the reference systems

We rarely update reference systems because updates can create significant changes to the published coordinates across Canada. Still, sometimes it’s simply necessary to correct systematic positioning issues. Below, you can learn about the status of the geometric, vertical and gravimetric reference systems used for positioning in Canada.

Geometric reference system

Although some users continue to work in legacy reference systems (e.g., the oil and gas industry in the North American Datum of 1927 [NAD27]), the current geometric reference system adopted by most jurisdictions in Canada and the U.S. is the North American Datum of 1983 (NAD83). It has evolved over the years and there have been many updates, but the fundamental system hasn’t changed for more than three decades.

That’s why the U.S. National Geodetic Survey is now modernizing its National Spatial Reference System (NSRS). They will replace NAD83 as their national geometric reference system with the North American Terrestrial Reference Frame of 2022 (NATRF2022). This update was originally planned for 2022 but has been delayed until 2025. This new system will be aligned to the new International Terrestrial Reference Frame of 2020 (ITRF2020) at epoch 2020.0 but will be fixed to the North American tectonic plate and will drift away from ITRF2020 as the tectonic plate moves about 2.5 cm/yr within the ITRF2020 frame.

The change in coordinates from NAD83 to NATRF2022 will be mainly due to a 2.2 m shift between the NAD83 and NATRF2022 origin at the Earth’s center of mass. The horizontal coordinate difference between these two systems will range from 1.3 to 1.5 m along the U.S.-Canada border.

For more than 100 years, Canada has maintained a common geometric reference frame with the U.S. Consequently, CGS plans to adopt NATRF2022 in parallel with the U.S. in 2025. CGS is working with the provinces through the Canadian Geodetic Reference System Committee (CGRSC), a federal-provincial government committee, to support their efforts to migrate to NATRF2022, with the goal of moving to a unified reference system across Canada.

For more information about what this means for Canada, consult this Geomatica paper and our summary pamphlet, Mind the gap! A new positioning reference.

Height reference system

In 2015, Canada adopted a new height reference system: Canadian Geodetic Vertical Datum of 2013 (CGVD2013). It replaced the Canadian Geodetic Vertical Datum of 1928 (CGVD28). The new system corrects for systematic errors in the old datum, and is also realized by a geoid model instead of a network of benchmarks whose heights are measured by levelling. We continue to publish heights in CGVD28 to assure a smooth transition.

Show me more about CGVD2013 and transforming between vertical datums (PDF, 1.2 MB)

The U.S. is also updating its height reference system. Just like we did, they are moving to a geoid-based vertical datum that’s compatible with global navigation satellite systems (GNSS). The U.S. will call its new datum the North American–Pacific Geopotential Datum of 2022 (NAPGD2022). Its release has been delayed until at least 2024. Fortunately, their height reference system has the same definition as CGVD2013, making our vertical datums consistent at the border.

Although we’ve agreed with the U.S. on the definition of the modernized height systems, we are still working out a few details:

• Should Canada make use of the name NAPGD2022 instead of CGVD2013 when the U.S. rolls out its new datum?
• Should Canada and the U.S. adopt a common naming convention for the geoid model, which would cover North America? If so, Canadian Gravimetric Geoid of 2013 (CGG2013) would be replaced by GEOID2022 (v1) and improved models would be recognized by an incremental version.
• Most importantly, NAPGD2022 would be a dynamic datum, i.e., the geoid would change shape as masses are redistributed. Currently, we neglect the small (-2 to 1 mm/year) temporal variation of the geoid in CGVD2013.

Gravity reference system

Currently, the Canadian Gravity Standardization Network (CGSN) is tied to the International Gravity Standardization Network of 1971 (IGSN71). Therefore, the datum is considered accurate to several tens of microgals (1 microgal = 10^-8 m/s²). We are currently updating the gravity network to the new International Gravity Reference System adopted at the general assembly of the International Union of Geodesy and Geophysics (IUGG) in 2015. CGSN will be adjusted by constraining it to absolute gravity stations (few microgals accuracy) distributed across Canada, allowing for better accuracy nationwide. The new adjustment will provide gravity values at epoch 2020.0 and a velocity model of the gravity field. The network should be known as CGSN2020.

Updates to the reference frames

A reference frame is never errorless; there are always uncertainties in the input information. As we collect more data and adopt improved models, theories and technologies, we improve the coordinates of the control stations in Canada.

Each time the International Global Navigation Satellite Systems Service (IGS) releases a new International Terrestrial Reference Frame (ITRF) realization, we produce a new version of the North American Datum of 1983 of the Canadian Spatial Reference System (NAD83(CSRS)). These new versions include more recent data and account for any new earthquakes and local disturbances of stations. Each new version represents a more accurate realization of the reference frame. Simultaneously, an improved velocity model is also produced in the new reference frame, which more accurately describes the motions of the Canadian landmass and enables positions to be more accurately propagated to different epochs. Figure 1 shows the evolution of NAD83 in Canada.

In 2019, CGS released version 7 of NAD83(CSRS). This version is based on a transformation from ITRF2014, the latest realization of the ITRF at that time. NAD83(CSRS) v7 is compatible with all previous versions of NAD83(CSRS) and uses the same 2010.0 coordinate reference epoch as NAD83(CSRS) v6. It also provides a more accurate realization of NAD83(CSRS) for both coordinates and velocities of the Canadian Active Control System (CACS) and the Canadian Base Network (CBN) stations. The coordinate differences with NAD83(CSRS) v6 at epoch 2010.0 are generally less than 1 cm, while the velocity differences are 0.5 to 1 mm/yr.

Differences in versions of NAD83(CSRS) have several causes:

• More years of observation at stations already in NAD83(CSRS)
• New stations filling gaps in coverage, especially in northern and remote regions
• The effects of earthquakes and other transient changes in position and velocity
• The re-processing of all GNSS data with the latest software and models (e.g., updated antenna calibrations, ionospheric and earth models, etc.)
• Changes in adjustment methodology

Reference frame epochs

Although each new realization of NAD83(CSRS) produces slightly improved control station coordinates, there are larger variations in coordinates over time due to crustal motion. We monitor this motion through observations at active control points in Canada and periodic re-observations of the CBN monuments. To account for crustal motion, survey agencies publish their NAD83(CSRS) coordinates at specific epochs.

Height reference frame

The update of the height reference frame requires updating the geoid model for CGVD2013. We released the original geoid model (CGG2013) in 2013, and developed an updated version in 2015 called the Canadian Gravimetric Geoid of 2013 — Version A (CGG2013a). This update consists of a regional improvement for the region of Lake of the Woods, which intersects the provinces of Ontario and Manitoba and the state of Minnesota.

We continue to improve the geoid model on a yearly basis. However, the next geoid model will only be published following the recommendation of the CGRSC, which includes representatives from federal agencies and all 10 provinces.

In addition, we are working with the U.S. National Geodetic Survey and Mexico’s National Institute of Statistics and Geography (INEGI) to develop a unified geoid model for North America, which will serve as the realization for NAPGD2022.

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