Centimeter-Level RTK Accuracy More and More Available — for Less and Less

February 4, 2014  - By 19 Comments
Eric Gakstatter

Eric Gakstatter

Last month, I started off 2014 with a bang by listing all the public RTK bases available in the United States, most of them being free. I received a lot of positive feedback and some enlightenment. For example, I didn’t know that in California, there are more than 330 RTK public base stations accessible by anyone for free via the California Real Time Network website at the University of California at San Diego! What a tremendous resource for California surveyors and GISers.

Remember that RTK will give you 1-2 cm accuracy horizontally and twice that for vertical. If you know that and also know that there are 330 free RTK bases in California, why would anyone use post-processing for high-precision (e.g., sub-foot) GIS data collection? RTK technology used to be reserved for people who could spend tens of thousands of dollars on a GNSS receiver. Not any longer. RTK receivers are available for under $7,000, and you don’t need to invest in a RTK base unit if you’re in range of a public one on my list (or a commercial one not on my list).

I’m pretty sure it was Charlie Trimble (founder of Trimble Navigation) who said “accuracy is addictive.” It sure is. Once you experience real-time centimeter-level accuracy (RTK) in the field, you won’t be satisfied with anything less, and neither will your GIS.

I’ll keep updating the List of Public RTK Base Stations in the U.S. as people continue to inform me of ones that aren’t on my list. If you know of one, please email me.

Keeping on the subject of RTK, 2014 might be the year of inexpensive RTK receivers. Whereas today you can find L1/L2 GNSS RTK receivers (in the U.S.) ranging from US$6,500 to US$25,000, there are rumors that some manufacturers are going to break through the US$6,500 price point.

This is in line with the prediction I made a few years ago, but for a different reason. In 2010, I wrote that RTK receivers would become very inexpensive due to the new L5 signal being introduced, which would increase competition among GNSS receiver designers. I speculated that with more competition, the selling prices would significantly decline. Well, we are still without a usable L5 signal (although making progress) due to the slow deployment of modernized GPS satellites and the delay in Europe’s Galileo system, but we are still seeing a steady decline in the price of RTK receivers. Why is this?

Even though there are a limited number of designers of RTK GNSS receivers, an increasing number of companies are buying RTK GNSS boards from these designers and making their own finished RTK GNSS receivers that look and perform very similar to receivers available today, for a fraction of the price. This is especially true in China, where there are several manufacturers buying RTK GNSS receiver boards from Trimble, Novatel, Hemisphere et al, making their own finished products and selling them. They were initially selling to very price-sensitive markets such as Africa, but now you see them setting up distribution in North America.

This “OEM Syndrome” has put tremendous price pressure on existing brand-name RTK GNSS receivers as the Chinese-equivalent products are priced as little as 25% of the equivalent brand-name products. Of course, this drives the leading brand-name companies crazy. They are forced to either drop their price or otherwise convince buyers that their products are worth a significant premium. During these times of tight capital budgets, it’s increasingly difficult to do the latter. When enough satellites are in orbit broadcasting the L5 signal, you’ll really see this effect gain traction because there will be a lot more RTK GNSS designs to choose from, and the result will be better quality. More competition always results in better product quality and performance.

The fact is that RTK receivers are moving towards becoming a commodity. As much as your local salesperson would like you to think they are selling a better RTK GNSS receiver, the technology gap between leading-brand designers and others is closing and probably unnoticeable to most of you. The major differences end up being the quality and reliability of the finished product (system design, battery, display, antenna integration, power supply, etc.). Having a great RTK GNSS receiver board inside is useless if the system design is unreliable.

More Real-time PPP Competition

For the longest time, it’s only been OmniStar (now owned by Trimble) and Starfire (owned by Deere & Co.) in the L-band high-precision correction game. Then, last year, the International GNSS Service announced its free decimeter real-time PPP service.  The catch is that receiver designers must incorporate IGS firmware to make use of the signal and…it’s only an Internet-based service (no satellite communications).

In the past couple of months, Hexagon (which owns both Leica and Novatel), made a bid for Veripos. Veripos operates an L-band GNSS correction service for the oil and gas industry. Last year, TerraStar, a subsidiary of Veripos, announced its new decimeter service that is very similar to OmniStar and Starfire. It uses satellite communications for a data link. Altus Positioning Systems incorporated the TerraStar service into its receivers. Hexagon is very close to closing the deal with Veripos and just last week announced a partnership with competitor Topcon Positioning Systems. The result is that Leica and Topcon both will start offering high-precision L-band GNSS correction services with their receivers. If you’re an L-band decimeter user, this is probably good news for you. More competition = higher quality and lower price.

Thanks, and see you next month.

Follow me on Twitter at https://twitter.com/GPSGIS_Eric

This article is tagged with , and posted in Newsletter Editorials, Survey Scene
Eric Gakstatter

About the Author:

Eric Gakstatter has been involved in the GPS/GNSS industry for more than 20 years. For 10 years, he held several product management positions in the GPS/GNSS industry, managing the development of several medium- and high-precision GNSS products along with associated data-collection and post-processing software. Since 2000, he's been a power user of GPS/GNSS technology as well as consulted with capital management companies; federal, state and local government agencies; and private companies on the application and/or development of GPS technology. Since 2006, he's been a contributing editor to GPS World magazine,writing a monthly newsletter on high-precision GPS/GNSS technology. He is also editor of Geospatial Solutions, a weekly newsletter focused on geospatial technologies.

19 Comments on "Centimeter-Level RTK Accuracy More and More Available — for Less and Less"

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  1. JJM says:

    As an offshore user, my positioning efforts are always DYNAMIC.
    Refresh my memory please: RTK is for STATIC (stop and go) surveying? Or has RTK advanced to be valid for dynamic (constant movement of measurement point) situations?
    PPP – I have used Starfix/Omnistar and CNav/Starfire with good results and have seen Veripos in operation. My experience with them is now several years old but as of the last usage my preference was the single small box of CNav with very stable results. I imagine that all 3 are now single box solutions. At the time (I believe it was all 3) you could hire the level of accuracy you required (centimeter vs sub-meter). Also note that Land Use subscription was afford-ably priced vs offshore use. Just to mention some items to consider when shopping.

    • Eric Gakstatter Eric Gakstatter says:

      RTK is real-time dynamic like Omnistar/Starfire except there’s very little convergence time with RTKK and RTK is more accurate than real-time PPP.

      Yes, all are single-box solutions now, albeit likely draw more power with L-Band and GPS combined. Antennas are also combined.

      • Bocephus says:

        The problem with RTK offshore is that there are few places to setup RTK base stations.

        • JJM says:

          Many State Waters can be covered by a land based station.
          Federal Waters can be a problem, UNLESS you are working with (and within 10 miles of) a fixed platform.
          You might be surprised how much of the Gulf of Mexico is provided cell phone coverage (not satellite based).

  2. Michael McGee says:

    As the technology and surveyors knowledge base advances it is important to common-ize the definition and use of terms. In my neck of the wood, we use “RTK” to refer to a local perhaps temporary base (single baseline solution) and “RTN” to refer to a real time network which usually provides corrections. The California Real Time Network (CRTN), although considered an RTN, presently provides a single baseline solution but is expected to be upgraded to a true RTN solution. By the way, the 341 CRTN stations are part of 850 California “CORS” stations (we call them CGPS) of which about 170 are included in the national CORS network.

    • Eric Gakstatter Eric Gakstatter says:

      Thanks Michael. I’ve been referring to something like the CRTN as an RTK Cluster (single baseline). You see a lot of those in agriculture. But, that name likely won’t stick. RTN and RTK nomenclature seems to be similar to the GNSS and GPS nomenclature. It’s hard, at least for me, to shake old habits.

      I’m still amazed at the tremendous high-precision GNSS resource that Californians have at their fingertips.

  3. Reg Parks says:

    Eric,

    The ever astute Michael beat me to the punch on the numbers and the acronyms. Geologically speaking, compared to the rest of the continental US, California is a rocket ship. For now, California is moving to Alaska slowly and steadily as well as in fits and starts. Because of our unique geological situation, scientists have had used GPS to monitor plate movement and seismic related change.

    Roughly 3/4 of our statewide GPS network sites are funded through limited term scientific monies. Before we get too comfortable with the concept of “universal RTK or RTN” we want to make sure that someone will be funding these networks, properly maintaining them and publishing all the necessary data and metadata to make the best use of them.

    Secondly, as advancing measurement technology continues to trim the error budget of surveying and especially GIS mapping; users will want to focus on methodology and coordinate system parity. The higher the precision the more detectable sloppy measurement technique will become. The correct selection and assignment of datums and coordinate systems and datum time alignment (epochs) will be a more significant factor, especially when working with data collected by different devices at different times.

    Let’s also not forget the vendors spec these devices under optimum conditions with highly trained users. Generally speaking, most users do not collect under the same conditions…and tree canopy is tree canopy no matter what they tell you. There is no silver bullet.

    For high precision work I’ll take a post-processed baseline and coordinate solution over an RTK baseline and coordinate solution any day. The main reason is that you can edit and clean static data to improve the solution. With RTK/RTN you get what “you” measure and what “they” solve. Also RTK/RTN is only as good as the radio or cellular link. In northern CA, the terrain and cellular tower availability can be a big factor in ANY signal reception continuity. Sure there is RT+infill (using it today) but then you are back to post processing.

    It’s all fun and getting better.

    RP

  4. Reg Parks says:

    Dude! Then there’s RTK with infill (static, not terrestrial)…It’s a hybrid blast man!!! Making my job today. Eric, RTK (in the right hands) is probably way fine for GIS topo/feature mapping which doesn’t require the higher precision like control, construction, boundary, deformation or geodetic surveys.

    Call me dorkey but I love getting in there and tweaking the guts of SV vectors to pump the SNR and see more ZEROES. Reg jonses for zeds (after the decimal point that is……………..

    Now, post processing resource grade (straight code phase) signal? That is a plain waste, of time; I agree. Spend the extra bucks and buy “centimeter” receivers, but learn how to use them to their max effectiveness………….. just sayin’.

    Now here is your next discussion concept….in your opinion does GIS mapping include stake out and design or just data collection?
    RP

    P.S………are you calling me OLD???

    • Eric Gakstatter Eric Gakstatter says:

      Reg, we are old. But we can run circles around the young guns :-)

      Yes, if you enjoy playing with satellite vectors, you are officially a dork. Accept it and move on.

      re: stakeout and design. Depends. I’ve taught architects and construction crews to use RTK for mass ex and feature staking. I have them check into project control first thing in the morning and last thing before leaving the site, and possibly some in between.

      Probably not curb&gutter…

  5. Dave says:

    Eric,
    You hit on two important words “local salesperson”. I am not one, I am a GPS user. The first two systems I worked with were purchased from and greatly supported by the “local salesperson”. Their help was very important to me in getting the systems up and running. But now, the last two (both network rovers, a Geomax and a CHC) I purchased were from mailorder shops. With my experience from using the first two systems, I was comfortable buying without the local salesperson support. Point being that if you are new to GPS, I would highly recommend buying from a local salesperson because that initial startup and the associated learning curve can be greatly reduced time-wise with someone standing next to you! The extra money up pay is worth it.

    • Eric Gakstatter Eric Gakstatter says:

      Hi Dave,

      Good point. The right local person can get you up and running fast. Glad to hear you are exploring the alternative brands.

      Eric

  6. Jon Proud says:

    I would like to brag about Oregon’s real time network (rtn), and Oregon coordinate reference system (OCRS) which are low distortion map projections. The Oregon department of transportation has put together a wonderful system for all the gps users to use for free state wide. It is a real positive addition to the public sector provided by a state agency making both more productive. Jon

  7. Michael McGee says:

    “You got to know when to hold em and when to fold em!
    I would caution users not to be dissuaded from static GNSS/post-processing, as RTK is not yet the best solution in all cases. We couldn’t have established the San Francisco “B” Order Deformation Network with RTK or RTN. However, our tests of the local RTN is proving to be consistent with the “B” Order Network at the centimeter level and less at times. We plan to formulate a high accuracy “RTN control” specifications and procedures for establishing the densification network.

  8. John W. Veatch PLS says:

    Professional Land Surveyors have been kept alive by things subsurface. Not minerals or oil or stuff like that but 1/2” iron rods set just below the surface so Joe Homeowner will not sue the guy who put it there because Joe Homeowner won’t hit it with a lawnmower. That said there is a residual value to this type of subsurface surveying to all the PLS’s of the world who deal in real property surveys. The fact is these iron rods or pipe represent Property Rights above and subsurface when are used to mark the corners of real estate. Because they are invisible to all of this hi-tech Lidar and other new field data collecting devices that, at 1000 XYZ coordinates a second, are keeping field data collecting PLS’s setting at their desk wondering what the hell has happen. And this is the very reason the airborne drowns, cars, trucks and all manor of mechanized field data collection systems will not (for now) replace “feet on the ground”.

    As GIS becomes more user friendly the applications will surely follow. This is not good news for land surveyors. To be sure computer technology has made the tedious simple and the digital revolution has made the storage and retrieval of a universe of information a mouse chick away. Even so when it comes to Digital Mapping in the USA what you think you see may not necessarily be what you get. This is particularly true of property lines drawn on public and private online image maps. I am referring here to the proliferation of geographic information systems in every burg and hamlet in the USA. In a misguided attempt to show property lines on government & private systems the locale GIS managers have resorted to all kinds of low tech approaches. The result has been the dissemination of misinformation that the uninformed would justifiably assume to represent the actual legal delineation of property lines.

    What appears to be missing in any discussions regarding Digital Mapping is the recognition of the fact that lines on a map, or in our new virtual world, do not necessarily represent those same lines in the real world. Even if the person or persons creating these lines uses real world coordinates and connects the dots they create, unless those coordinates & connecting lines were created as a result of a real world professional land surveyor’s standard of care the lines connecting those dots cannot possible represent legal property lines.

    Maybe GIS really does mean “Get It Surveyed”

    Historically parcel level geographic information has been the realm of the professional land surveyor. Yet because of the utility of GIS, amateurs have taken over the process of deciding just what and how land parcel data will be represented on the internet. Even now it is very late in the game for surveyors to attempt to put a stake in the ground (pardon the pun) and claim what is legally and should rightfully be theirs. So how do we get back in the game? My suggestion would be to gather the resources and build a “Real Property GIS” using the new Lidar Mapping Headset I am developing. We are about to once again redesign the land surveying profession however this time we have a specific purpose that that will take 10s of thousands of property owners (some paying over $1000,000/yr.) out of a FEMA flood zone and save them a billion or 2 in insurance payments and my Lidar device is the key to the process. We are interested in exploiting freely available signals including GPS, cellular, digital television, and wireless LAN (e.g. WiFi), SCP based Doppler Aided Inertial Navigation (DAIN) determines location through a sensor fusion approach. Combining inertial, magnetic, and gravity data with the SCP RF observables, DAIN provides continuous position, velocity, and direction information to produce datasets and make them commercially available. So if you or your company would be interested in becoming one of my strategic partners; join me I know the perfect place to start.

    You can call me in my Florida USA office my direct line is 1-239 282 9170

    • Eric Gakstatter Eric Gakstatter says:

      Hi John,

      I agree that technology is squeezing the land surveyor. Surveyors must find a way to adapt or consider a career change. The good news is that there are lots of opportunities for properly-educated/skilled surveyors to solve problems that GIS managers are running into.

      You might want to take a look at the Nightmare on GIS Street articles I wrote last year.

      http://geospatial-solutions.com/nightmare-on-gis-street-accuracy-datums-and-geospatial-data/

      http://geospatial-solutions.com/part-2-nightmare-on-gis-street-accuracy-datums-and-geospatial-data/

      The bad news is that value of high-accuracy spatial data rapidly declining because it’s much less expensive to collect it with today’s technology and it is only going to become cheaper, so if your business is locating stuff, then look out.

      The “Get It Surveyed” phrase is a good chuckle, but that’s about it. GIS isn’t driven by accuracy. A perfectly good GIS could have spatial accuracy of +/- 100 feet and serve the purpose it was built for. GIS us driven by the database. Accuracy is secondary, and surely depends on what purpose it serves. Would it make sense for McDonalds to spend the $$ for a GIS database accurate to a tenth when trying to determine where to build its next restaurant? Certainly not.

      Is the accuracy of GIS parcel databases good enough to serve their intended purpose? Maybe not for your purpose, but was it built for land surveyors?

      No one would disagree that they would like a more accurate parcel database. The question is who would pay for it?

      Eric

  9. Tigre says:

    Hey Eric!

    What are your thoughts on the Swiftnav Piksi RTKS units? Do you think they can compare to the more expensive/established units? Any direct use/exposure with them?

    Thanks!

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