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Corrections Services Abound

January 25, 2023  - By
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While single-base real-time kinematics RTK can, under specific conditions, be the best option for certain applications in surveying and construction, corrections services typically eschew this solution in favor of network RTK, PPP, and PPP-RTK. There are, though, some agricultural networks made up of clusters of reference stations delivering RTK corrections. (Images: courtesy of Gavin Schrock and Courtney Townsend
Bigmouse108/iStock / Getty Images/Gettu Images)

The boom in the development of corrections services for applications such as autonomy and robotics has brought a whole new slate of market players, and an expansion of services from established corrections providers. This has benefitted high-precision users as well as the new not-so-high-precision applications.

Whereas very high precision — centimeters — is of paramount importance to sectors such as precision agriculture, construction automation, surveying and mapping, new market sectors are less concerned with precision as they are with reliability, availability and resilience. There are many corrections services that can deliver reliable lane-level precision, decimeter precision, sub-meter or whatever the application requires.

Corrections have been around in various forms for nearly 30 years. Whereas traditional high-precision applications would access corrections services or network infrastructure directly, the user of a mass-market application, such as assisted or autonomous driving, receives corrections second or third hand.

A car manufacturer may install an integrated navigation and positioning system (GNSS is typically only one of many technologies in a complete system) from a vendor that receives corrections from one or more corrections services.

A Recap of the Technology

Uncorrected GNSS is limited to precisions in meters. This may be fine for many purposes, such as coarse navigation and local-based apps. However, for high precision uses, external augmentations (commonly referred to as “corrections”) add more and higher accuracy data to help mitigate multiple sources of error that otherwise limit standalone GNSS results. Various augmented data can be delivered via radio, the internet, or communications satellites. Delivery of augmentations by public or commercial generators of this add-on data is broadly referred to as “positioning services.”

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Network RTK, implemented as real-time networks (RTN), covers hundreds of localities, states, and entire countries and is a go-to for many applications in surveying, mapping, construction, monitoring and agriculture. One disadvantage, compared to PPP, is reliance on terrestrial IP communications. (Images: courtesy of Gavin Schrock and Courtney Townsend
Bigmouse108/iStock / Getty Images/Gettu Images)

There are two fundamental approaches to generating corrections: Observation Space Representation (OSR) and State Space Representation (SSR). OSR uses observations of one or more base receivers to derive correction values representative of local conditions. Examples of OSR include base-rover real-time kinematics (RTK) and network RTK (NRTK). SSR provides “states” of conditions derived from terrestrial tracking networks, to improve clock and orbit “products,” and may also include data from global, regional, or localized ionospheric and tropospheric models. Examples of SSR include precise point positioning (PPP) solutions.

Players in the corrections services sector include vendors who manufacture GNSS hardware, RTK systems, and NRTK software. One example is real-time networks (RTN), which have grown to cover hundreds of localities, states, regions, and even entire countries. Some of these vendors now operate their own wide region RTN. The same large vendors also have developed global PPP services. The most recent decade though has seen rapid growth in new corrections service providers that focus on one or more key markets and develop approaches specifically to serve them. For instance, many agricultural regions of the world have large clusters of RTK stations operated by a vendor or a cooperative. Some newer vendors, focused on the autonomy market, have developed global PPP services, regional NRTK, or hybrids for decimeter to meter precision. One Achilles heel of PPP is its relatively poor vertical precision compared to RTK and NRTK. This partly explains why adoption has been slow for certain high-precision applications, such as surveying.

Where corrections services have become quite interesting, is in amalgams of these approaches. In recent years, the rapid expansion of corrections services for mass-market applications has given rise to what developers call PPP-RTK. Ostensibly, this is to take advantage of the strengths in each approach, however it may be more about trade-offs between precision and the practicalities of serving wide regions in a cost-effective manner. There are many variations on how this hybridization is achieved; for example, PPP- ambiguity resolution (PPP-AR). PPP-RTK can be somewhat of a nebulous term, much in the same way as the term “AI” gets used. Developers of the specific PPP-RTK approaches for the many corrections services keep certain details close to their chests. Clients are less concerned with how it works as they are with the results.

Examples of Vendors

In compiling the following list, we tried to provide examples of all aspects of the corrections service industry — from GNSS network software development to hosting of national and regional networks to providing global PPP. This segment continues to grow; new players continue to develop solutions and enter the market, some with great fanfare, while others seek to stay under the radar. This list does not include the many hundreds of RTN worldwide — local, regional, or national — though the key providers of the NRTK software these networks use are listed.

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One advantage of PPP and PPP-RTK over RTK and NRTK is that they can deliver augmentations by satellites, eliminating reliance on terrestrial communications networks. Satellite delivery has a downside: the number of communications satellites broadcasting the augmentations is limited, which can be problematic in sky-view challenged areas. (Image: courtesy of Gavin Schrock and Courtney Townsend
Bigmouse108/iStock / Getty Images/Gettu Images)

Note that other vendors are also not listed, such as some that seek to limit their visibility to specific clients and partners. For example, some offer corrections services as an adjunct to inside hardware/software sales, and others work with developers of certain integrated navigation/autonomy systems. In addition, some of the smaller vendors may be working in conjunction with some of the more established developers, often licensing elements of their software, and in many instances piggybacking on their global tracking networks.

In alphabetical order:
Atlas. From Hemisphere GNSS. A global PPP service delivered by L-band satellites. It includes tiered precision for different applications, such as surveying, mapping, and asset management. Atlas Basic, Atlas H30, Atlas H10: bit.ly/3V42qxj.
CHCNAV. CPS NRTK software: bit.ly/3FI6zlN. It also hosts various RTN and has a global network partner program: bit.ly/3VQugOr.
CNH. Advance Farming Software (AFS) RTK+ network delivering corrections mostly via cellular to primarily precision agriculture users: bit.ly/3YiCZur.
DigiFarm. DigiFarm VBN. An example of another network that serves primarily agriculture users, however, it now has a spinoff to serve other high precision markets: bit.ly/3hgnYZs.
eSurvey. GNSS NET, a VRS management software: bit.ly/3Py0uMp.
Fugro. Global PPP corrections services; tiered precision for various applications, mostly maritime and marine construction. StarFix, SeaStar, MarineStar, OceanStar: bit.ly/3W4LkA8.
Geo++. One of the first developers of GNSS network and PPP solutions. Its GNSMART software suite provides NRTK and SSR broadcast capabilities: bit.ly/3FhGE2Z. 
HERE Technologies. HD GNSS, a PPP-RTK solution for mass-market applications: bit.ly/3Fnle4H. 
Hi-Target. Hi-RTP, a global PPP- RTK service: bit.ly/3hi2xHv. 
IGS. International GNSS Service, a federation of agencies and research entities with a global tracking network of more than 400 reference stations. The IGS is a vital component of the global geodetic infrastructure. RTS is its real-time PPP service. It is not fast converging like many of the commercial services, but it is free for many applications. It is not broadcast via satellites, only via the internet: igs.org.
Leica Geosystems. Part of Hexagon. Provider of NRTK software (Spider), and host of its own RTN covering various regions around the world (SmartNet), and global PPP (SmartLink): bit.ly/3uEwHb9. 
NovAtel. Part of Hexagon. Includes various tiers of PPP-RTK: RTK Assist, RTK Assist-Pro*, TerraStar-L, Oceanix, TerraStar-C PRO*, and TerraStar-X* (what NovAtel calls “RTK From the Sky”): bit.ly/3HzuqWh. 
Point One. RTK correction service called Polaris, available also via partners such as Bad Elf: bit.ly/3uPJGqA.
Premium Positioning. RTK corrections service called RTK Premium: bit.ly/3uT0xZi. 
Rx Networks. A mix of tiered positioning approaches for location- based applications. Truepoint. io (DGNSS, PPP, PPP-RTK): bit.ly/3We1rvT. 
SBAS (Public). Satellite-based augmentation systems, national or regional services. Like commercial PPP, SBAS corrections are mostly served via satellites. Public safety and civil aviation are the primary drivers for providing such services. For instance, in North America, the Wide Area Augmentation System (WAAS) was chartered by the Federal Aviation Administration (FAA). There are equivalent systems in Europe (EGNOS), India (GAGAN), Japan (MSAS and QZSS), Russia (SDCM), China (SNAS/BDSAS, which is still in development) and Australia and New Zealand (SouthPAN). Other systems are in development in South America and the Caribbean (SACCSA), Korea (KASS) and in Africa and the Indian Ocean (ASECNA). 
Sino/Comnav. CDC.NET CORS software, RTN software: bit.ly/3W56hvm. 
Swift Navigation. Skylark RTK and Skylark DGNSS services: bit.ly/3HyWVn5. 
Tersus GNSS. Tersus Advanced Positioning (TAP), a PPP service: bit.ly/3hoZkWD. 
Topcon. TopNet and Topnet Live. RTN Software, regional RTN, and PPP services: bit.ly/3FRRcaw. 
Trimble. RTN software, VRS Now (regional RTN), and tiered PPP services: CenterPoint RTX, RangePoint RTX, ViewPoint RTX, and FieldPoint RTX: bit.ly/3V3bbax. 
u-blox. PointPerfect regional PPP and PPP-RTK: bit.ly/3FPVmQo. 
Veripos. Part of Hexagon. Tiered global PPP services, originally focused on maritime applications: Standard, Ultra, APEX: bit.ly/3BBjfsf. 
Verizon. Telecom infrastructure-based PPP-RTK service called ThingSpace: bit.ly/3Fw1U55. 
Vodaphone. Currently developing corrections services in conjunction with Topcon: bit.ly/3Pug4s0. 

Whatever the application, there are now many options for corrections services. Non-mass-market applications, for traditional high- precision uses, have been tapping such services for (in some cases) decades. The prize of primacy in the autonomy market has been in the sights of many of these vendors for many years, yet there have been relatively few real-world applications to date. That should be changing soon. Early adoptions such as GM’s Super Cruise, which is powered by the same core PPP technology as RTX, have been quite successful. Which will come out on top? That might be a moot question. With the potential of such markets so great, perhaps there is room for all of them, and more. 

About the Author: Gavin Schrock

Gavin Schrock is a practicing surveyor, technology writer and operator of a cooperative GNSS network.