PPP: IGS Announces the Launch of RTS-IGS
Professional Surveyor Magazine - May 2013
By Gavin Schrock, PLS
If anything underscores the fact that high-precision, global, real-time GNSS is real, viable, and here for the long run, it is the news that the International GNSS Service (IGS) has launched an open access real-time precise-point-positioning (PPP) service. While a few years behind some commercial (and sometimes proprietary) real-time PPP services, this international cooperative of scientific and academic partners (formed to serve geodetic and geophysical research and reference frameworks) launching RTS-IGS is a truly significant development on many levels.
On April 2, 2013 the International GNSS Service issued a press release announcing a real-time, global (and free) GNSS precise-point-positioning service. To fully understand why this news should be viewed as significant for surveyors, we need to back up a bit and answer a few questions, like what is the IGS, and what is PPP? An examination of these questions can be found in the article “Beyond RTK” in the June 2012 issue of Professional Surveyor. A thumbnail of these two terms is:
IGS – International GNSS Service:
An international cooperative of scientific, academic, and respective national geodetic concerns, such as JPL, NASA, the BKG (the federal geodesy and cartographic agency in Germany), Geosciences Australia, Natural resources Canada (NRCAN), and many more—too many to mention. Key for surveyors to consider is that the IGS is a service of the International Association of Geodesy (IAG) and the Global Geodetic Observing System (GGOS), and surveyors are going to be exposed to more global geodesy in coming years. (It might be hard to see how so many countries could agree on such matters, but as one IGS wonk mused “the politicians cannot agree on anything, but the scientists can.”) But what do all of these affiliations and acronyms do for us? The earth-centered-earth-fixed reference frameworks (ECEF) that we are increasingly dependent on are established, operated, and maintained by these entities, and as the National Geodetic Survey (NGS) moves to closer alignment (and eventual full adoption of) the International Terrestrial Reference Framework (ITRF), the Earth itself (and the framework stewarded by the IGS) becomes the upstream geodetic reference. In short: the IGS is like the NGS for the whole globe.
PPP – Precise Point Positioning:
A method to achieve high-precision positions from GPS (and GNSS) uses primarily very precise orbit and clock data (from global and regional tracking systems) applied to the observations of a receiver. There are many kinds of tracked “products” that different flavors of PPP can use, such as clock, orbits, global and regional ionospheric models, and more. This has long been used for post-processing and through many free services like those hosted by NASA and NRCAN. But as Dr. Georg Weber has said on several occasions, “Why produce a daily newspaper if you are only going to deliver it once a week?” contrasting post-processing services with real-time. There are real-time products produced by the tracking infrastructure of the IGS and by commercial entities serving their own customers in key markets like precision agriculture, marine, and energy exploration. PPP is increasingly available via real-time services (RT-PPP), like those of John Deere, Fugro, Veripos, Trimble RTX, and others. These are for-fee and/or proprietary authorized services, and the “products” are made available via real-time internet and/or satellite broadcasts. These private entities have established their own tracking capabilities to add local augmentation and refine their products for their customers with amazing results.
There are two key reasons why the real-time PPP service of the IGS (RTS-IGS) is significant despite being a few years behind the commercial RT-PPP and arguably lower precisions (at this time). One is that the service is free—there’s no other way paint that as anything but significant. The other is that this new service is (or will become) an integral component of the ITRF, sharing the same tracking network, references, and contributing players/entities.
But what does RTS-IGS deliver? If you have a decent dual (or even single) frequency receiver, with a decent antenna, you can fire it up anywhere in the world, and if the receiver is capable of processing the type of PPP products from the service (or you run one of a number of open-source applications like BNC or RTK-LIB on a laptop), and provided you have a live connection to the internet, you can (after an initial convergence time of 15-30 minutes) start taking decimeter level (or better) shots. Sounds like a lot of hoops to jump through for what a survey would likely consider low precision, but if you’ve ever tried to resolve geodesy in a remote part of the world then this can start to look like a godsend. Many surveyors already utilize post-processed PPP, and many involved in energy exploration, geotechnical, resource management etc, already utilize some of the commercial RT-PPP services (which have an edge with shorter convergence times and precisions). While this may not be quite ready for primetime for commercial development and residential cadastral surveys (but never say never; it can only get better), there are those who are chomping at the bit where use may be appropriate.
Developers and researchers have been testing some of the IGS products, and once advance word got out of the impending launch of RTS-IGS, end users signed up and began testing and production usage. One such user, from an international geotech firm, told me excitedly the day of the launch how he took a $250 receiver, attached geodetic rover antenna, ran RTKLIB (open source at rtklib.com), and got decimeter precision testing in his backyard here in the U.S.
Above are results from a 30-day test of the service by the Bundesamt für Kartographie und Geodäsie (BKG). The results are not stellar (if compared to RTK), but this is achieved without localized infrastructure, is resolved to the ITRF in real-time, and is free. It will only get better.
Resolving the fourth “D” of the ITRF in real-time is the other key point of significance, and probably the one with the most lasting impact. A labyrinth of legacy national, regional, and local systems has been developed to realize geodetic values, and the complexity has been compounded by having to reconcile temporal changes in published values for passive control—infrastructure that is becoming much harder to fund. Much of this may be by-passed, carefully and with proper procedures, in the future through the use of tools like RTS-IGS, which is precisely why the IGS has developed such tools. None of this affects the legal primacy of physical cadastral monumentation, but instead further enables the use (where appropriate) of geodetic tools in establishing relative positions for, and even preservation of, such valuable infrastructure.
Dave Doyle (retired NGS and now geodesy editor for PSM
) commented on the news, “This could really be a game changer. If the results [can soon be] in the range of just a few cm, I wonder if this won't have an impact on [timelines] for pushing new geometric datums. A goal has been to roll out the geometric and geopotential [gravity-based vertical] datums at the same time, which really makes good sense. However, if everyone can start getting ITRF/IGS coordinates at the few cm level now then I suspect that this may force a re-think of that [timeline]. It will be interesting to see how this all shakes out.”
When will we see this on our rovers? Developers I contacted indicated that development was well under way, and there are indeed PPP-enabled devices (typically for niche, scientific, or industrial uses) on the market. The specific Initial Operating Capability (IOC) documentation for RTS-IGS has just been released, and a notice to GNSS manufacturers from IGS states: “NTRIP-based streaming of GNSS correction data enables world-wide, highly accurate Precise Point Positioning (PPP) following the State Space Representation (SSR) approach wherever mobile communication is available. As NTRIP is an RTCM standard, no licensing is involved regarding stream transport or stream format, allowing GNSS equipment manufacturers to freely integrate this functionality into their products. To encourage this, IGS will consider on a case basis providing generic company accounts for the RTS broadcasters that allow direct access to the RTS correction streams without specific user registration. Once GNSS equipment manufacturers incorporate this functionality into their receiver firmware, RTS will be directly accessed through receivers having a built-in PPP capability.”
You could expect to see this capability (or similar commercial services) in the release notes of the next (or soon thereafter) firmware releases of some types of rovers.
For some surveyors the IGS announcement could be viewed as a prime example of what people mean when they say, “I have good news for you and bad news for you, but it is the same news.” Such a service holds promise for (at least future) uses by surveyors, but it can also waken that gorilla in the room of fear that soon high precision positioning will be in the hands of anyone and everyone. That notion would be fodder for a much longer discussion (and likely a heated one). But inasmuch as the positioning cat is already pretty much out of the bag, perhaps this news, and that of RT-PPP in general, should be viewed as an opportunity. There is more to the surveying profession than just measurement. Some non-surveyors may try the measurement part, but without the skills and knowledge of full context, a “precise” measurement in the wrong hands can only do them harm. For surveyors it is better to know what is coming down the pike than not—we should stay on top of such developments. PSM will continue to follow PPP and related developments closely.
Gavin Schrock, PLS is a surveyor, technology writer, and operator of an RTN. He’s also associate editor of this magazine.
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