Category Archives: gps

Something Interesting From Trimble

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I’ve been expecting one (or more) of the major survey & GIS data collector manufacturers to come out with something like this for some time now. I’m not surprised that Trimble was first out the gate. It’s called the Trimble Leap.

Trimble Leap

If you understand what’s going on with this new product you realize it’s a fascinating concept. It’s not just a small GPS receiver mated to a smartphone via Bluetooth – that capability has been available for a few years now. What this receiver provides is more advanced GPS signal tracking and the integration of Trimble’s RTX GPS data correction service. Trimble’s RTX service is a virtual reference station (VRS) system that receives GPS data corrections using the smartphones’s cellular data connection. This allows the Leap receiver to provide on-the-fly GPS positional accuracies that are less than 1 meter. Remember sports fans, the best your smartphone or Garmin Nuvi can do is about 15 feet, and that’s on a good day, under open skies, with lots of GPS satellites available.

Keep in mind that the Leap is not a survey grade device. It’s a lower precision field data collection device. The kind of thing a utility company would send a work crew out with to collect manhole locations. For applications like utility data collection, sub-meter accuracy is just fine.

The Leap concept is the next evolutionary step to take smartphones into the high accuracy/precision GIS data collection role. Smarphones are really just small computers with built-in modems, so they are the ideal computing platform for applications like this. However, smartphones have one huge Achilles heel – battery life. An ‘always on’ Bluetooth connection and cellular data connection will suck a smartphone battery dry in just a few hours. This is not a Trimble issue, but something that must be taken into consideration when putting devices like these into the field to collect a day’s worth of data. Better make darned sure you’ve got that in-car phone charger along with you!

There are still a lot of unknowns with regards to the capabilities of this system. Is the Leap receiver GLONASS capable? Does it allow data collection without the RTX connection? What about cost? I’ve read reports that the Leap hardware will run just under $1,000 and the RTX data correction service will be an additional $400/year per device. If you have any understanding of how much RTK compatible GPS receivers cost, and how much a VRS data service costs you will realize that $1,000 for the hardware and $400/year for the data service is a bargain.

Where I think Trimble stumbles is that they have slaved the Leap to their Terrain Navigator Pro (TNP) software. My impression is that TNP is a moribund product and Trimble is trying to breath some life into it by slaving it to a very capable hardware package. My hope is that Trimble quickly migrates the Leap software interface to other products like its own TerraFlex cloud service and even develops a plug-in that allows Leap data streams to be read by products like ArcGIS Online mobile applications.

– Brian

Some GNSS Musings

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First things first – GNSS is the new GPS.  Actually, GPS is a subset of GNSS. GPS stands for Global Positioning System, GNSS stands for Global Navigational Satellite System. For decades folks refereed to any and all satellite navigation systems as GPS, and for good reason – the US Global Positioning Satellite system was the only game in town. However, the term ‘GPS’ properly describes just the global positioning system established and maintained by the United States. Now that the Russian GLONASS system is operational, and systems from the European Union, China and perhaps other players (India?) are coming on-line, the term for ALL space-based satellite navigation systems has shifted to GNSS.

OK, now that that’s out of the way.

I spent the last two days in training finally learning how to run Trimble’s TerraSync and Pathfinder Office software.  We’ve had TerraSync and Pathfinder Office software in our office for years, but never got any formal training on how to use either package.  The training was actually very good, and I can see now why a lot of surveying and engineering firms prefer TerraSync over GIS-centric packages like ESRI’s ArcPad.

The class was taught by one of the training and support personnel from our local vendor, NEI, and he did a great job.  Woven throughout the class are discussions about GPS, datums, coordinate systems and issues like unanticipated coordinate system shifts due to improper datum selection or datum mis-matches between the software and virtual reference station (VRS) datums.  We spent a good deal of time in the field actually experiencing the impact of changing datum selections in the software (for example, the shift seen when selecting NAD83 vs. NAD83 HARN).

So this class got me thinking again about GNSS and data quality and accuracy…

In the olden days, like before the turn of the century, these datum shifts generally didn’t concern GIS folks.  The shifts introduced by any datum mis-match were well within most folk’s error budgets.  In most cases we were ecstatic when GPS got us within a few dozen feet of the features we were collecting.  When the accuracy standard of the 1:50,000 topographic map you were using as a base was +/- 50 meters having GPS points a dozen or so feet off was no big deal.  In fact, we were tickled pink to be able to get that level of autonomous GPS accuracy.

Today things are much different. Improved GNSS software, antenna designs, the open availability of reliable GPS and GLONASS signals and the wide availability of GPS augmentation services like WAAS and local virtual reference stations (VRS) means that these systems are capable of sub-meter, often sub-foot, accuracies. That’s just for GIS data collection.  Survey-grade GNSS systems are capable of real-time accuracies to tenths of a foot. Suddenly datum shift errors of even one foot become very, very important for high precision data collection and surveying.

One of the biggest problems people in my line of work face is a general lack of understanding of GNSS in the GIS and civil engineering fields. In particular, many professionals lack up-to-date training and working knowledge of GNSS system capabilities, limitations and application to their line of work.  Evaluating and planning for the potential impact of things like datum shift on GNSS-based surveys or data collection projects is something they can’t comprehend largely because they haven’t been trained on it and, perhaps most important, have’t been forced to consider it when planning or managing a project.

Sadly, I’ve met far too many people with a GISP certificate hanging on their wall who couldn’t tell me the fundamental difference between the NAD 27 and NAD 83 datums, and I have yet to meet a single civil engineer who is not also a licensed surveyor who could explain to me the importance of knowing the datum his or her CAD drawing coordinate system is based on.  Yet both of these groups – the GIS professional and the civil engineer – have a fundamental interest in controlling the overall accuracy and precision of their work.  For the GIS professional it’s a matter reputation and trust.  For the licensed civil engineer it could be a matter of putting his or her work at legal risk.

If you work in the GIS field you can not call yourself a GIS professional unless you have a fundamental understanding of datums, coordinate systems and the importance of applying this knowledge to your workflows.  A strong knowledge of datums and coordinate systems is one of the foundational building blocks of our profession, and since so much of what we do these days is GNSS-based it makes it equally important to have a strong understanding of the impact different datum selections can have on the spatial quality of our data.

I’ve said before in this blog that those GIS ‘professionals’ who consider GIS to be little more than making web maps are headed to extinction. Here in the Atlanta metro area it would take me about an hour to hire a busload of web developers who can make web maps (and this includes time out for a stop at Starbucks). If that bus accidentally rolls into the Chattahoochee River and everybody drowns I can get another busload just as fast. However, the number of GIS professionals I’ve run into who can tell me the anticipated shift in State Plane (NAD83) and State Plane (NAD83 HARN) coordinates wouldn’t fill the first row of that bus.

For the civil engineering community the issue is less obvious but just as critical. GNSS-based surveying and data collection is becoming the norm on many projects. It is faster, cheaper and just as accurate as conventional surveys under the right conditions. This means civil engineers will be incorporating more and more GNSS-based data into their designs and relying on GNSS for jobsite control, machine control and as-built data verification. While the task of establishing project control, setting up survey equipment configurations and managing project survey requirements will fall to the the project surveyor, the project engineer still has overall responsibility for ensuring things are built to design.  If the project stakeout is a few feet out from the design drawings it may not be because the instrument operator has a hangover; it may be because the design work was done in one datum and the GNSS survey unit is set to another. Being able to identify a potential datum shift problem is a key skill for civil engineers working in today’s GNSS-based world.

– Brian

GPS

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I’ll make this quick.

I’m deep into preparing a briefing/presentation/class on the issue of magnetic declination and the easiest rules to follow when you need to apply it.

What’s magnetic declination, you ask?  Sorry, that’s not the topic of today’s post.  If you really – REALLY – need more information right now check out the Wikipedia page on Magnetic Declination.  I’ll be referring to it in a later post.

Anyway…  I was mentioning to a friend that I was working on this presentation and he commented “Does anyone really care about that anymore?  I think everyone has just gone out and bought a GPS.”

I actually get that reaction a lot when I talk to people about compasses and using a map and compass to navigate.  “Compasses confuse me.  I’d rather just use a GPS” seems to be the common refrain.

(For the uninitiated, GPS stands for Global Positioning System, or space-based satellite navigation system.  There are several operational (US, Russian) and developing (the European Union’s Galileo) satellite navigation systems, but ‘GPS’ has become an almost a generic term used to describe the US developed and operated NAVSTAR system.)

I live and work in the world of GPS.  I’m a geospatial professional and I run the GPS-based survey and data collection program at the World’s Busiest Airport.  Every day I am thinking about, using, training, developing policies on and attending meetings about GPS and how we use it at our airport.  Everything from upgrading our high-precision GPS receivers to providing airport-specific input for the FAAs GPS-based NextGen precision approach program to review and quality control of project layouts generated using GPS-based survey systems.  And more.

I am the biggest cheerleader for the GPS system and GPS-based technologies.  GPS is perhaps the best example of a project that only the United States could do, and do right.  The driver who switches on his Garmin Nuvi for the drive to the airport is leveraging tens of billions of dollars and decades of research, development, testing, deployment, maintenance and upgrades.  All paid for by the US taxpayer, and all free to any user anywhere in the world.

Conceptually the GPS system is simple – satellites in space broadcast their position and your receiver (example – our driver’s Garmin Nuvi) uses time shift calculations to determine the precise distance from your location back to the satellite.  Once the receiver picks up and processes signals from at least two more satellites it can triangulate your position.  The size of the position ‘triangle’ determines the accuracy of the position fix provided by the receiver, but in general a modern receiver tracking three or more good satellite signals can locate you to within about 15 feet of your true position anywhere on earth.  That’s pretty damned good by anybody’s reckoning.

GPS has revolutionized many industries and spawned completely new ones.  GPS systems are so pervasive that most people no longer give them a second thought.  Today GPS technology tracks your package as it travels from the retailer to your door, and it tracks the paroled felon sporting the nifty ankle bracelet.  GPS technology manages the hand-off of your phone conversation from one cell tower to another as you speed down the interstate, and GPS technology guides the angle of the bulldozer blade working a local road construction project.  Anything that locates you on a map is universally identified as ‘GPS’, even if the function has nothing to do with satellite-based navigation.  GPS has become an integral part of our lives and impacts us for the better every day.

And yet, GPS is a system with serious limitations.  It can’t locate you indoors, in tunnels, under overpasses, in dense forests or even in the man made canyons of large cities.  The signals can be easily corrupted, blocked or bounced around so much they are virtually useless.  The entire GPS system is a delicate balance of high technology and rocket science, enormously expensive to maintain and upgrade.  At some point the GPS system – certainly a system that succeeds what we have now – will fail.  It will fail due to funding shortfalls, political upheaval, changing national priorities or simple neglect.  This failure is merely a recognition of a historical inevitability – man made systems always fail at some point.

Long after the GPS satellites go cold and dark in their far orbits and GPS receivers become little more than technological oddities, the magnetic compass will continue to offer reliable wayfinding.  Using a compass (along with a map) is not easy or intuitive for most people, but once learned it provides a reasonably accurate, reliable, steady and ‘always on’ navigation capability that can not be turned off by man’s whim or neglect.  I feel fairly certain that at some time in mankind’s future we’ll be back to navigating using the simple, reliable magnetic compass.  It’s inevitable.

That’s why I still practice my map and compass skills.