Survey & Construction Newsletter, Late September 2008

September 17, 2008  - By 0 Comments

ION GNSS Conference – Not This Year

Well, it wasn’t meant to be. Hurricane Ike made sure of that.

I travel quite a bit and I never fly Continental Airlines, but there aren’t a lot of choices when flying to Savannah, Georgia from Portland, Oregon. So a couple of months ago, I booked my flight to Savannah on Continental with a connection in Houston, Texas.

Hurricanes and Houston don’t mix well this time of year. Anyway, Hurricane Ike wreaked havoc on southeast Texas. Houston’s airports were closed for the weekend (my flight was supposed to depart last Sunday). Continental, being a small airline with limited routes, couldn’t get me to Savannah until Wednesday night at the earliest. Other airlines were jammed up trying to reroute people around the Hurricane-affected airports.

So be it … no ION conference for me this year. Too bad, it’s my favorite conference of the year because I get to see where companies and organizations are putting their research effort which, in turn, gives me a good idea where GNSS technology for surveying/construction is heading.

At ION, one of the things I was scheduled to do was give a presentation at the Civil GPS Service Interface Committee (CGSIC) meeting on Monday. This year is the first time the CGSIC is allocating GPS World a slot on the agenda. The topic of my presentation was entitled “WAAS for Mapping: It Works Where You Work.” So, instead of presenting it at ION this year, here you go.

First of all, let me tell you that even though the applications featured are focused on WAAS, this is really about SBAS (satellite-based augmentation systems) in general. That includes MSAS (Japan), EGNOS (Europe) and soon, GAGAN (India).

Trends in GPS mapping

The user community expects GNSS technology products to become smaller, cheaper, simpler, and higher performance.

For the most part, we have seen that trend develop in the past decade. GPS mapping products have migrated from heavy, backpack-based systems with a medium-sized dome antenna, DOS-based data collector, VHS recorder batteries, antenna cable, data collector cable, and power cable to the small handheld devices and small receiver boxes of today. Likewise, prices have fallen considerably. The market prices for a sub-meter mapping system are 50 percent to 60 percent 60 less than a decade ago.

The GPS mapping user community is moving away from post-process differential correction and towards real-time correction.

The reason is quite simple: simplicity and cost. Post-processing is a pain and it’s expensive. It’s not just the cost of the software and software maintenance contracts, it’s the personnel training to stay current on the software, it’s the cost of time to post-process and it’s the cost of not having real-time data in the field. Yes, there is a cost of not having timely data.

One of the arguments for post-processing is that it’s more accurate. From a pure scientific standpoint, that’s a correct statement, but it’s crazy to make that sort of general statement. I could show you data that shows that statement is correct and also incorrect. Like most answers to GPS accuracy questions, the answer is, it depends: it depends on the receiver, it depends on the application, it depends on your personnel qualifications, etc.

SBAS makes real-time GPS correction simple and cheap, as in free. WAAS has matured over the last five years since it was declared operational from providing 1 meter to 3 meter accuracy to where it is today, providing accuracies of well under a meter in the continental United States, Alaska, Mexico, and most parts of Canada. The simplicity and low-cost of SBAS makes sub-meter mapping attainable by a larger percentage of the user community.

All WAAS (SBAS)-Enabled Receivers Aren’t Created Equal

One of the common experiences with WAAS (SBAS) in mapping applications is that the user will attempt to use a consumer-grade GPS unit (eg. Garmin) and, predictably, the performance will be poor. Consumer-grade GPS units aren’t designed for accuracy. They are designed for fast satellite acquisition, low-power consumption, low-cost, and easy user interface.

I don’t know if you’ve been paying attention, but the newer consumer-grade GPS units don’t mention SBAS like they used to. It’s because the difference between autonomous positioning and WAAS-corrected positioning isn’t a significant issue with respect to the average GPS consumer who is navigating from point A to point B. Go look at the mapping Handhelds section on the Garmin website. There is no mention of WAAS in the specs. The reason? Garmin doesn’t care about WAAS for the ground user.

If the GPS manufacturer does care about WAAS for ground users, there is a lot they can do to optimize the use of WAAS (SBAS) so it can perform in environments where a standard WAAS-enabled receiver couldn’t dream of working. One technical paper on this subject was published by Stanford University and presented at the ION conference in 2006. Euiho Kim, Todd Walter, and David Powell from Stanford presented a paper entitled Optimizing WAAS Accuracy/Stability for a Single Frequency Receiver.

Some manufacturers have done this and more to exploit WAAS so it can be used in environments where a receiver implementing the traditional use of WAAS couldn’t. I can write about this until I’m blue in the face, but the proof is how the user community is using WAAS with high-performance receivers in applications where many people say WAAS can’t be used. I know of a few of them around North America and have provided a short synopsis of each to give you an idea.

Applications of WAAS in North America

Company: J.D. Irving Ltd.
Employees: 15,000
Industry: Forest products
Location: Eastern Canada
Application: harvesting timber
User Statement: “The general misconception is that WAAS doesn’t work under forest canopy. (For us) It’s proven to be a false assumption if the right receiver is used.”

Company: American Forest Management, Inc.
Employees: 250
Industry: Forest management
Location: Virginia to Texas, Maine to Michigan
Application: Area calculations, forest road work, land owner mapping
User Statement: “Our field efficiency has drastically increased due to reliable reception and ease of use … office productivity also increased because of real-time correction.”

 

Company: Portland General Electric
Employees: 2,600
Industry: utility
Location: Oregon
Application: utility pole mapping
User Statement: “Four years ago, we started out using low-end WAAS receivers, but switched to mapping-grade WAAS receivers after 60 days due to accuracy problems. 225,000 poles and four years later, we are still using the same WAAS receivers.”

Company: State of Minnesota
Employees: a bunch
Industry: state government
Location: Minnesota
Application: mapping abandoned chemical facilities
User Statement: “Approximately 500 facilities were mapped using a Bluetooth, sub-meter WAAS GPS and a Windows Mobile data collector. Wireless technology eliminated connectivity problems and the receivers had COAST technology, consistently giving us submeter, real-time results, even in areas that had poor visibility.”

Company: U.S. National Park Service
Industry: federal government
Location: sub-arctic Alaska
Application: map archaeological sites
User statement: “Many mapping grade GPS users still do not feel good about relying on WAAS. You can always post-process, but after reading these numbers, some may ask why bother?”

Other Related Trends in Real-Time GPS Mapping

Not only is WAAS (SBAS) being exploited by some manufacturers of sub-meter GPS mapping equipment, some manufacturers have introduced survey receivers that also exploit WAAS, but use another satellite observable for centimeter-level positioning rather than using the WAAS correction itself.

In optimal scenarios, this potentially adds another two observables when resolving ambiguities for RTK positioning.When manufacturers start designing products around a technology, it speaks highly of the future of that technology.

RTK networks (RTN) are experiencing explosive growth around the world.

It’s a relatively new technology that will add to the proliferation of real-time users for both RTK and sub-meter mapping systems. RTN’s primarily cover metro areas at this time, but some countries have recently announced the implementation of country-wide RTNs. Look for more editorial coverage on this in the future.

Commercial DGPS services have shifted from offering L1 sub-meter DGPS products to decimeter L1/L2 products in certain regions in the world.

DGPS signal providers have recognized that WAAS/SBAS fills the requirement for sub-meter corrections where it’s available. They haven’t stopped offering L1 sub-meter DGPS corrections, but certainly have shifted their focus to the GPS L1/L2 market.

On The Not-So-Positive Side of Things

We’ve enjoyed many years of relatively quiet ionospheric activity. In a sense, we’ve taken for granted the awesome increase of GPS accuracy (both autonomous and DGPS). This is going to change as the next solar cycle cranks up. It’s an 11 year cycle that began early this year and will reach its high point in 2011 or 2012.

What’s so bad about solar activity?

For GPS users, errors induced by significant ionospheric activity can be measured in meters or even tens of meters even if you are using a DGPS correction source such as WAAS, beacon or RTN. Some experts say the next solar cycle will be worse than average. Some say not. All of them say “we won’t know until it’s here.”

Read more about Solar Cycle 24 here. The subject is worthy of an entire article; which I will write in the coming months.

Be sure to watch the live coverage that my fellow editors will be providing from the ION GNSS conference in Savannah this week.

This article is tagged with and posted in Newsletter Editorials, Opinions, Survey, Survey Scene
GPS World staff

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