I just noticed the Indiegogo campaign for the Reach GPS receiver at www.indiegogo.com/projects/reach-first-affordable-rtk-gps-receiver which promises a small GPS receiver with cm level accuracy. I think it gives a view of what will be possible with GPS in the future.

The device is small, cheap, and uses open-source software and an ublox chip that can record at 18 Hz. Nice start. But the really interesting part is that it uses RTK GPS. I read a little about this, and did not really understand most of it. But it seems that the potential precision is in the millimeter range because the a more than 1000-fold higher frequency is used (compared to the normal GPS units) to get rid of atmospheric distortions. This also requires the use of two receivers - a stationary one that acts as reference, and the normal moving one. However, the stationary one can be used to many moving receivers. What's more, the cost for two receivers (with enough CPU power to do the calculations) is less than $500.

The "RT" part in RTK GPS stands for "real-time". This requires that the two units are connected by radio, Wi-Fi, cellular, or similar (the stationary unit can basically be connected to a web server). That might be impractical for windsurfing. However, it seems that post-processing is also possible, so the corrections could be done later at home.

The technology promises absolute position accuracy of 2 cm. I think that requires that the position of the stationary unit is known to this level of precision. However, I think the relative position accuracy should always be in this range (assuming a good GPS signal, etc). I think at this level of accuracy, the positional speed data could actually be more accurate than doppler speed data.

The units will probably be first available for drones. The developers (emlid.com/) are already selling an autopilot chip, the Navio+, for drones. that includes a ublox GPS for less than $200. The chip includes not just a ublox-based GPS, but also a bunch of other things the autopilot needs, including wi-fi and servo outputs.

Any geeks out there looking for a project? The Reach receiver should be available within a month or two, maybe even before the new Locosys becomes available. You'll have to hook up your own screen etc, though. But you do get a "9DOF IMU" with 3-axis accelerometer, so you can spend many windless days in front of a computer, trying to figure out how to use the acceleration data to further improve speed accuracy .

You probably should add a warning that if you follow the link to the Indiegogo site, you will end wasting heaps of time just looking at all the really,really cool gadgets in development.

Essentially, as I understand it, Carrier wave RTK with differential correction is what they Survey Grade GPS's use. The Trimble units that are used by Macquarie Innovation and Hydroptre are based on this system and technology.

I know of other projects that are developing RTK GPS devices that could be quite inexpensive, practical and affordable for GPS Windsurfing, and possibly work easily with other current hardware and devices for levels of accuracy that are order of magnitudes better than the current best we use.

It is my understanding that such devices can produce Doppler speed data with incredible accuracy as well. The advantage of Doppler may still remain as it is less susceptible to atmospheric interference.

It is amazing that despite our small market to drive specialist GPS development, we may well have what is now almost unimaginable accuracy available to us in the not too distant future at a very modest cost.

The survey grade equipment like Trimble etc use L1 L2 GPS data, the L2 containing the essential differential correction. The system Reach is developing is only L1. I looked at a similar system back when I first developed the GT11 in 2006 and then, as now, realised without L2 there is now way to get cm accuracy. Even using a base station and logging error data the weak point was the antenna on the moving GPS. Essentially you needed a helmet sized antenna to get the required signal strength. Doppler speed measurement is still the most accurate way of determining how fast we are going. Doing it at 10hz or higher rates is the easiest way to improve accuracy, just like the U-Blox system I developed back in 2008.

It'll be interesting to see how it develops.

As roo said, without the second GPS providing corrections off a known point, the gps that surveyors use really aren't mucho better than a gt31, accuracy wise. They've just got a lot more fuctions....

As I understand it, survey gps already use real time too

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Roo said..
The survey grade equipment like Trimble etc use L1 L2 GPS data, the L2 containing the essential differential correction. The system Reach is developing is only L1. I looked at a similar system back when I first developed the GT11 in 2006 and then, as now, realised without L2 there is now way to get cm accuracy.

Well, a lot of things have changed since 2006. You pointed out a few years ago that GPS chips in phones have reached a high level of accuracy. A lot of the positional speed data on the $60 phone I'm using are darn close to the GT-31 doppler data. The Reach developers seem to understand the importance of the antenna, seeing that they have a $60 antenna in their perks, and that they suggest using a heavy antenna for the base station.

The documentation from Trimble published in 2006 about their RTK GPS does indeed state that they used L2 data to get better precision. But the explanations on Wikipedia state that RTK improvements can come just from using the L1 carrier wave phase. In a sense, this seems similar to doppler - we are looking at phase shifts for more accuracy. The improvements from using L1 carrier phase tracking come from the higher frequency - 1575.42 MHz, compared to 1 MHz for the C/A code that is normally used. The theoretically possible improvement in accuracy (to +- 1.9 mm) is rather impressive. I have a feeling that this level of improvement is significantly higher that what is possibly with Doppler data. The typical error numbers we get for Doppler data certainly point in this direction.

I have not checked into the history, by I believe that a lot of these improvements have become possible only after 2006. Version 1.0 of the open source software they are using, for example, was released in 2007.

Never underestimate what market forces will do to technology. The drone market is already a multi-billion dollar market, and GPS position is critical for many commercial drone applications. The production issues that the Reach guys deal with are not "How do I get $50K to design a water-proof GPS case for windsurfing" (which stopped the development of a Flysight-based GPS), but rather "How can I get a sufficient quantity of the Intel chips we need for the system".

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Subsonic said..
It'll be interesting to see how it develops.

As roo said, without the second GPS providing corrections off a known point, the gps that surveyors use really aren't mucho better than a gt31, accuracy wise. They've just got a lot more fuctions....

As I understand it, survey gps already use real time too

Difference is price. The Commodore PET was a few thousand dollars, the Sinclair ZX with similar power about $100 or $200. Neither was even 1/1000th as "smart" as any $60 smartphone you may use for GPSLogIt.

The stationary GPS is no big deal. For speed, we only need relative accuracy. Leave one of the two units you can buy for less than $500 on the beach, take the other one sailing. Don't even worry about the "real time" part - just post-process the data. You can still get feedback that's at least as good as the GPSLogIt or GT-31 data on the water just from the ublox GPS, even without the carrier-phase magic.

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boardsurfr said...

Subsonic said..
It'll be interesting to see how it develops.

As roo said, without the second GPS providing corrections off a known point, the gps that surveyors use really aren't mucho better than a gt31, accuracy wise. They've just got a lot more fuctions....

As I understand it, survey gps already use real time too

Difference is price. The Commodore PET was a few thousand dollars, the Sinclair ZX with similar power about $100 or $200. Neither was even 1/1000th as "smart" as any $60 smartphone you may use for GPSLogIt.

The stationary GPS is no big deal. For speed, we only need relative accuracy. Leave one of the two units you can buy for less than $500 on the beach, take the other one sailing. Don't even worry about the "real time" part - just post-process the data. You can still get feedback that's at least as good as the GPSLogIt or GT-31 data on the water just from the ublox GPS, even without the carrier-phase magic.

Forgive me for being skeptical, I find it a little hard to believe that the gps technology has gotten to the point where they could get 2mm accuracy. Survey gps gets about 30mm accuracy, with corrections.

Don't get me wrong, it's great news if we can start getting that kind of accuracy with an off the shelf gps.

Survey grade GPS are capable of 1cm and have been for quite some time*. Initially, some may have needed 15+ min's of geostationary time to resolve to that level, but now I think they can get it in real time. When Macquarie Innovation was using the Trimble system back in 2007-8, they were claiming better than 10cm accuracy in Dynamic mode with differential correction at 10hz.

The figure of 1.9mm quoted for RTK is the theoretical possible accuracy. I don't think anyone is claiming they have actually attained that level yet, at least not in a practical application.

Current (in the last couple of years) RTK developments using just L1 and Differential correction in real time from a dedicated second unit in a known location nearby, can do 1cm now, or very close to it, in real time. This capability has already been demonstrated using consumer grade GPS chips and relatively small antenna. With the developments underway, it is just a matter of time before solutions become available at very affordable cost that we can use.

After looking into it some more, I agree with Boardsurfr that centimetre level positional accuracy (with accuracy error data), looks like it will far surpass what is currently possible with Doppler speed data. At this very moment though, and probably for the next couple of years, the Ublox Doppler data at 10hz is about the best we can get access to.

However, it is worth noting that Survey grade GPS's have gone from around $60,000 in the early 2000's, to under $7,000* now, and even to $320!** And the models available have increased a lot.

For about $7,500 you can even have this hand held beauty and send data to your smartphone or tablet! www.gpsworld.com/gnss-systemaugmentation-assistancenewsgeneq-introduces-palm-sized-gpsglonass-rtk-receiver-real-ti/

* gpsworld.com/centimeter-level-rtk-accuracy-more-and-more-available-for-less-and-less/

** gpsworld.com/hemisphere-gps-announces-rtk-network-compatible-s320-survey-system/

Stop taking Andrew off topic. Any time he spends on the theory of 1.5cm accuracy of survey systems is time he is not spending on ratifying GPS equipment for gpsteamchallenge.

This website, gpsworld, is a great source of interesting info.

Here is a bit about an NMEA dongle that can connect to a GPS source, like a Survey grade GPS, and transmit the data via bluetooth to a IOS iPad or iPhone, over riding the internal IOS GPS and providing the IOS apps with extremely accurate locational data.

The interesting comment is this:

"Garg explained the need for the dongle on his Kickstarter page: "The accuracy and precision of the internal GPS on iPads and iPhones is highly unreliable - it works fine for navigational purposes but fails miserably for mapping and asset management applications. The accuracy varies in range from a few meters to a few hundred meters depending on operating conditions, and there is no easy way to reliably ascertain that. Tests have proven that the accuracy rating on the location data returned by Apple is more of a general estimate than a reliable metric."

You can see two important points here:

1. Accuracy not that great.
2. Can't quantify accuracy.

That is the same problem with any phone I'd say.

www.gpsworld.com/kickstarter-launched-for-nmea-dongle-to-connect-gps-ios/

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John340 said..
Stop taking Andrew off topic. Any time he spends on the theory of 1.5cm accuracy of survey systems is time he is not spending on ratifying GPS equipment for gpsteamchallenge.

LOL!

Actually, today I spent about 6 hours reacquainting myself with some of the finer points of GPS theory and educating myself up to date with recent progress. It all helps....

Plus, I am fascinated but some of the stuff I learned today........

Like this little tidbit:

www.gpsworld.com/gnss-the-new-gps/

China has launched its own GNSS system and it now has the most satellites in view in the sky to use (with GPS and Glosnass), more than Europe and North America. More sats used = better accuracy and reliability.

But guess what?!

Australia is covered by those Chinese sats as well! That means when, or if we have GNSS devices that can use China's BeiDou system as well as GPS and Glosnass, we will have potentially greater accuracy as well! Many of you will have noticed that most phone now use both the GPS and Glosnass satellite constellations. I don't think it will be long before they use the Chinese BeiDou system as well!

Thanks for all the clarifications, sailquik. If we had a GPS that delivers highly accurate position data, we could use the correlation between doppler and positional speed to set error margins.

The big thing that gets me excited is seeing market forces in action. We are using ancient GPS technology with the GT-31 because the market for a windsurfing GPS is maybe a thousand units a year. Anyone who puts in more than $50K in development of a new unit will have to be very patient if he wants to make a profit. The GP102 is available and a lot cheaper because it was made for a market that is at least 100x larger. But it does not do all we need, and cannot be changed. The Thingsee also was developed for a much larger market, but has an open firmware model, so it can be adapted. Cool. The Reach also is open software based, and cheaper. Very cool.

Once the market drives it, the technology will follow. When we set out to sequence the first human genome 25 years ago, the technology was not there yet. Most scientist thought the idea was crazy, and the cost of several billion dollars seemed ridiculous. When a Nobel prize winner got up at an early genome sequencing conference and predicted that we would not only beat the deadline, but that it would be possible to sequence a human genome for less than $1000 before today, almost everyone thought he was crazy. Well, he was right, and they all were wrong.

The total cost of the Human Genome Project was about $3 billion, spread over more than a decade. That has driven a technology improvement that exceeded Moore's law. Sequencing cost has dropped more than ten thousand fold over the last 15 years. So if you have an open, rapidly growing market that runs several billion dollars per year where GPS technology is a critical component, it is quite likely that GPS technology will improve dramatically. Typical RTK systems still cost a few thousand dollars, but most of them are in high-tech tractors or used for high-cost surveying. Once they become a common component in drones that sell for $1,000, their cost will drop dramatically. The Reach is just an example of this happening.

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sailquik said..

However, it is worth noting that Survey grade GPS's have gone from around $60,000 in the early 2000's, to under $7,000* now, and even to $320!** ...

** www.gpsworld.com/hemisphere-gps-announces-rtk-network-compatible-s320-survey-system/

The S320 retails for about $7000 (more in Australia, of course). The Piksi RTK system is available at store.swiftnav.com and costs $1000 for two receivers.

But there has been at least one report that "RTK GPS for Under $200 Works!" at www.isoblue.org/posts/2014/04/RTK-GPS-Under-00-Works/

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sailquik said..
Survey grade GPS are capable of 1cm and have been for quite some time*. Initially, some may have needed 15+ min's of geostationary time to resolve to that level, but now I think they can get it in real time. When Macquarie Innovation was using the Trimble system back in 2007-8, they were claiming better than 10cm accuracy in Dynamic mode with differential correction at 10hz.

The figure of 1.9mm quoted for RTK is the theoretical possible accuracy. I don't think anyone is claiming they have actually attained that level yet, at least not in a practical application.

Current (in the last couple of years) RTK developments using just L1 and Differential correction in real time from a dedicated second unit in a known location nearby, can do 1cm now, or very close to it, in real time. This capability has already been demonstrated using consumer grade GPS chips and relatively small antenna. With the developments underway, it is just a matter of time before solutions become available at very affordable cost that we can use.

After looking into it some more, I agree with Boardsurfr that centimetre level positional accuracy (with accuracy error data), looks like it will far surpass what is currently possible with Doppler speed data. At this very moment though, and probably for the next couple of years, the Ublox Doppler data at 10hz is about the best we can get access to.

However, it is worth noting that Survey grade GPS's have gone from around $60,000 in the early 2000's, to under $7,000* now, and even to $320!** And the models available have increased a lot.

For about $7,500 you can even have this hand held beauty and send data to your smartphone or tablet! www.gpsworld.com/gnss-systemaugmentation-assistancenewsgeneq-introduces-palm-sized-gpsglonass-rtk-receiver-real-ti/

* gpsworld.com/centimeter-level-rtk-accuracy-more-and-more-available-for-less-and-less/

** gpsworld.com/hemisphere-gps-announces-rtk-network-compatible-s320-survey-system/

Hmm sounds like they have come aways then, in a short space of time.

The Leica GPS we used surveying in 2010 could get 1cm accuracy, but as you say, it involved a period of stationary time to log it. They never maintained a constant 1cm accuracy though, they would generally hover around the 1.5/2cm mark. which is why the company i worked for never stated any better accuracy than 30mm with a gps survey.

Maintaining 1cm accuracy on a moving target would be very cool....

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boardsurfr said..

sailquik said..

However, it is worth noting that Survey grade GPS's have gone from around $60,000 in the early 2000's, to under $7,000* now, and even to $320!** ...

** www.gpsworld.com/hemisphere-gps-announces-rtk-network-compatible-s320-survey-system/

The S320 retails for about $7000 (more in Australia, of course). The Piksi RTK system is available at store.swiftnav.com and costs $1000 for two receivers.

But there has been at least one report that "RTK GPS for Under $200 Works!" at www.isoblue.org/posts/2014/04/RTK-GPS-Under-00-Works/

Opps! I blame may ageing eyes! "Should have gone to Spec Savers!" lol!

You know I actually went back to check what I thought was the price because it sounded to low to be true, but I still saw it as $320 instead of S320.

But you are quite right. These things will get a lot cheaper in the near future and the high accuracy technology will merge into consumer priced devices costing a few hundred dollars.

I think this guy is correct, and this was way back in 2010, long before the idea of low cost RTK took off:

In response to this claim: "Consumer-grade GPS receivers and survey-grade GPS receivers are not the same quality and never will be."

He says:

"This isn't the case according to several GNSS receiver designers I've spoken to. There's no reason a "consumer-grade" L1/L5 GPS receiver can't achieve cm-level precision (horizontally and vertically) with a good quality antenna. Of course, it will need a source of correction, but in the 5-10 year window, RTK corrections will be more available and less expensive than they are today. The RTK corrections will likely be free so the only expense will be the wireless data plan.

There will be dozens, maybe hundreds of GPS chipsets designed for L1/L5. Many will be open systems where companies will be able to load their own firmware into the receiver to add specific features (e.g., more robust ambiguity resolution for surveying). The baseline L1/L5 GPS receiver may be only a few hundred dollars, but a customized version for specific applications will have a premium of a few hundred, or maybe $1,000+. For example, a GPS L1/L5 receiver that also includes Galileo signal and is customized for machine control with specific features might be $1,500. Commercial users will pay that premium. They already justify paying tens of thousands of dollars for the same performance today. The difference is that a low price point will attract a much larger audience.

There's no doubt that there will be boutique, niche GPS L1/L5 receivers that will be able to garner a premium price, but surely the days of many thousands of dollars for high-precision GPS receiver are heading to an end."

Extract from:

gpsworld.com/surveynewsfollow-whats-going-happen-when-gps-accuracy-cheap-10082/

Love all the enthusiasm but the reality is 1 cm level precision in a stand alone hand held unit will never happen in my lifetime. What we have now is simple and works, other than a signal from gps satellites it's a stand alone unit. It doesn't need a base station setup, a connection to a data correction source, complicated programming etc. Right from the beginning I wanted a simple unit that anyone could use, the most difficult thing is posting your results online! Humans love complicating things, that's easier to do than making something simple. The accuracy of doppler based speed measurement is well documented, it will be many years before a positional based stand alone unit can match it.

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Roo said..
Love all the enthusiasm but the reality is 1 cm level precision in a stand alone hand held unit will never happen in my lifetime.

You're probably right about the 1 cm precision; typical real-world precision claims are 2 cm to 8 cm. Although your "not in my life time" reminds me a lot of what people said early in the Human Genome Project. Several articles come to mind where the authors painstakingly explained by it would be impossible to exceed the current performance by much, claiming physical limits had been reached or similar. They were proven wrong within a few years, as others discovered how to get around the limits.

In the United States, many states already have public base station networks, where the necessary reference data can be downloaded for free*. The state I live in, Massachusetts, has base stations spaced about 50 km apart**. Two of these are within less than 10 km of a speedsurfing location, and thus close enough. They state "the MaCORS Network Solution typically achieves an RTK accuracy of 1-2 cm horizontally and 2-3 cm vertically."

Your comments regarding simplicity are certainly valid. There are several members in our GPSTC team who find posting data quite challenging. Some of them like the ka72.com site, which simplifies things for them. Setting up a similar web service that analyzes raw GPS data is not much harder. The service could either load the reference data from the web automatically (if available), or require the upload of a second file from a reference station. So maybe that's twice as hard.

Regarding the accuracy of doppler data, I usually have a hard time finding anything that contains actual data, other than Tom Chalko's original paper. Sure, spikes are much less common, and having accuracy estimates is great. But what is the actual accuracy?

For GT-31 data, typical errors (given by GPSResults) for single data point in speed around 30 knots are +-0.5 to 1 knots. 10 second run errors are typically +- 0.3-0.5 knots. That's 1-2% accuracy.

For 5 Hz ublox data, I get errors of +- 0.3-0.6 knots at speeds around 30 knots. That's 1-2%. That goes down to +- 0.15 knots when looking at 10 second runs. 0.5% accuracy.

If we had positional data with an accuracy of +-3 cm (relative to the base station, not absolute), we'd also have an accuracy of +-1-2% for 1 second data points, since 30 knots is about 3 m/sec. But the error model for average speed changes! To get Doppler speed for 10 seconds, we average the individual speeds. By assuming that errors are random, we get lower errors when looking at more data points - either longer runs, or higher frequency data. Of course, if there is a systematic error in the doppler speeds, our accuracy estimates will be incorrect.

For positional data, however, the errors do not accumulate. If any point has a precision of +- 3m cm, the expected error for two points that are 10 seconds apart is +-6 cm or less. 6 cm of 30 meters is 0.2%. That's better than 5 Hz doppler data.

Note that for 500 m record runs, using positional data is actually conceptually more similar to gate timing than using Doppler speeds. Again assuming 3 cm errors, but allowing for 3 sigma on both ends, the observed time different to cross a distance of 500.18 m would give us a reliable estimate of the minimum achieved speed. Adding the 18 cm "safety" would add an expected error of 0.036%. For comparison, the +- error margins I get in GPSResults for 500 m runs are around 0.8% for GT-31 data, and 0.3% for 5 Hz ubox data. So positional data could actually be substantially more accurate, even at +- 3 cm.


* www.gpsworld.com/finally-a-list-of-public-rtk-base-stations-in-the-u-s/
** macors.massdot.state.ma.us/spiderweb/frmIndex.aspx

As I said will never happen in my lifetime! You are talking about a connected system still, I'm referring to a stand alone system that relies only on the data from the sats, doesn't need any other connection. Currently the sats don't provide enough information to correct to cm level positional accuracy for a small handheld unit with built in antenna. Once you start connecting multiple devices i.e. antenna, base station, MaCORS etc it is no longer stand alone system. It all gets complicated and opens up the possibility for more errors. KISS

Comparing positional data and velocity opens up a different can of worms. Two totally different measurements that are like apples and oranges. One measures displacement from a position and the other measures directional movement. At the end of the day measuring displacement to cm level accuracy will always be more accurate and provable but not possible with a hand held stand alone unit in my lifetime or until they put more powerful gps sats into orbit the broadcast the necessary correctional data. Measuring 3D velocity is simple, accurate and we have it already.

How long do you plan to live Roo?

Actually, it is here right now. 1cm positional accuracy in real time in a single, stand alone device.

A device receiving signals from many satellites plus a base station without the need for the user to have any other device is no different from what we do now. What is the difference if one of the many signals a GPS receives comes from a free, land based station or even over a mobile phone connection from the internet?

The WSSRC accepts the Trimble GPS units for their records, and, at least when they were first approved, they were only 8-10cm claimed accuracy. It is possible to get that now from other RTK devices that don't use a signal from a land based station, just from satellites.

Unfortunately for us, all that still still costs 7,000 dollars plus, but it will not for too long.

So the only real question is, will the stand alone GPS with 1cm real time precision become affordable for windsurfing in your lifetime?

I certainly hope it will because I hope to see you still around here for at least a few more years.

I agree entirely about simplicity. But of course, simplicity is just related to the user experience. For user simplicity it is just a matter if having clever designers who can mask the underlying ultra complexity from the user so as to provide him with a solution at the press of a few buttons. As you mention, we already have that available if you so desire. It's also easy to conceptualise systems which have even more complexity under the skin, but still with the same simple interface that anyone who can program a VCR can use. (Or use apps on a mobile phone? )

But of course, all this does not change the current reality that 5hz and 10hz Doppler based devices are the best we can do for speed precision at the moment for a few hundred dollars.

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sailquik said..
A device receiving signals from many satellites plus a base station without the need for the user to have any other device is no different from what we do now.

Exactly.

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sailquik said..

The WSSRC accepts the Trimble GPS units for their records, and, at least when they were first approved, they were only 8-10cm claimed accuracy. It is possible to get that now from other RTK devices that don't use a signal from a land based station, just from satellites.

Unfortunately for us, all that still still costs 7,000 dollars plus, but it will not for too long.

So the only real question is, will the stand alone GPS with 1cm real time precision become affordable for windsurfing in your lifetime?

Interesting to hear about the Trimble. My original post was that a 2-unit GPS with accuracy in the cm range at an affordable price is on the horizon. If the WSSRC things 8-10 cm is good enough, then why argue about "1 cm" vs. "3 cm"? Seems rather pointless.

But an affordable GPS system with cm resolution is already available - the Piksi. Claimed accuracy is 2 cm, better than the initial trimble. Size (53 mm) is small enough for windsurfing. Cost for a receiver is $500, comparable to the ThingSee. You'll need a base station for another $500. But together, it's still cheaper than a new race sail or speed board. That is now.

How relevant is that? What if you could get the WSSRC to accept the Piksi as a Trimble alternative, and then take a few units to Lüderitz? Rent the canal after the main event for cheap, without having to pay for gated speed measurements. Use a Piksi, and get world-record class data. For less than the cost of the flight + board transportation. Oh, and the Piksi does 50 Hz. According to prevalent thinking that higher Hz rates are better (which I do not totally buy into), that alone is an argument to use it.

I'm not really advocating to use the Piksi. I am just using it as an example that an affordable system is available already. Hobbyists who want to use if for a drone will argue against the "affordable". So there is plenty of incentive to develop comparable systems that cost less. The reach is just one example, at roughly half the price of the Piksi.

The potential relevance for the user? Allow me one more little leap of faith, even if we risk leaving Roo behind again. Let's assume someone takes the Reach and packages is like the ThingSee, with the screen, data storage, and software. That person is smart enough to market it to skiers, bikers, and other sports that have 1000-fold more participants than windsurfing, and to keep it open source (or at least customizable). The unit is set up so that it can function as a "standalone", as Roo defines it, or as an RTK system. It can also log raw GPS data for later offline analysis (e.g. though a web server that hides all complexity from the user).
Now we have a top-end system that is at least comparable to the ThingSee, and thus superior to the GT-31 and the GP102, even in standalone mode. Anyone who wants additional accuracy, say for record attempts or speed events, can add a base station. As the unit becomes popular with skiers (who routinely pluck down $1000 for new skies) and bikers (who don't think twice about spending $5000 on a decent bike), public base stations proliferate, and RTK online or offline analysis becomes the standard, even if you do not have your own base station.

Will that happen in Roo's life time? That only depends on how long Roo will live!

I had to search around a bit to find confirmation of my memory of conversations with Tim Daddo from the MI team.

This is from: www.trimble.com/technologyandmore/i3-2010/Download/TM%2016HQWEB_.pdf

the relevant quote is:

According to the International Sailing Federation World Sailing Speed Record Council (the governing body of the WSSRC) Rules 2010, the GPS survey equipment receiver logging rates must be set at 10 hertz, which results in a GPS position every 1/10th of a second. The GPS must also provide a time stamp with each position accurate within .001 second. The data needs to be so precise that a horizontal position error (hpe) of greater than 0.10 meter (one sigma) will not be accepted.

Note that no other GPS devices had been approved for use by the WSSRC at the time this article was written. I suggest this is mainly because someone would have to put a lot of effort into the validation of the accuracy in a form that the WSSRC would accept. It's probably a lot easier to just use the device that already has approval. I am pretty sure there would be many other GPS device around now that could perform at least as well, if not quite a bit better than the Trimble device approved over 10 years ago.

Another quote from the same article:

“The advantage of using the Trimble system is that it allows us to take the fastest 500-meter stretch from any high-speed run, rather than just a time between two fixed points,” says Paul Larsen, Vestas SailRocket’s team leader. “Using the 5700 means we can simply look at the GPS data for the day and pick out the fastest 500 meters wherever it happened.”

This is a very important concept that came about as a result of the MI syndicates earlier work to get approval for the speed timing cameras to be mounted on Yellow Pages, rather than on the shore. A number of surveyed markers were set up on the shore 500m apart for the cameras to reference. They were able to use any of the marked courses depending on the prevailing conditions. It is then not a very big leap to have the GPS mounted on the boat measure the best 500m speed anywhere in the course area.
It is clearly established (and has been for a very long time now) that for the WSSRC 500m records do not need to be set between two fixed points on the earths surface. You can sail for much more than 500m and simply take the fastest 500m section recorded anywhere along that course.