GPS World

Tag: editorial

  • Out in Front: An SVN up for Grabs

    Wednesday evening, September 23, Savannah, Georgia, 5:30 to 7:00 p.m., Session P2b — a date that will live in GPS history. The 400 to 600 of us who were there to witness it will never forget it. The SVN-49 Review Panel.

    Unprecedented puts it mildly.

    The ION program read: “SVN49 (GPS IIR-M 20) was launched in March of 2009 to support GPS constellation sustainment as well as to bring into use the new third civil signal, the L5. During the early orbit check out of this satellite, out-of-family measurements were observed impacting the legacy GPS L1 and L2 signals. The panel will review the background, current status, issues, and options moving forward with SVN49.”

    Col. David Goldstein, chief engineer, GPS Wing, gave a frank and open history and description of the situation. The panelists explained the options under consideration for partial fixes — a complete fix and eradication of the pseudorange error is not possible — and added a few remarks, but were mostly there to answer questions and provide perspective in response to opinions from the floor.

    It reminded me — now this is a leap — of a climb I led in days of yore up Mt. Kilimanjaro. Or escorted, really; the Swahili-speaking Tanzanian porters did all the leading. About two days in and a third of the way up, we realized that because of a schedule change we had made earlier for longer safari in the Selous, we didn’t have quite enough time to climb the mountain in the accepted manner and still make it back down for the once-weekly flight out. So over muesli and mangos the next morning in the A-frame hut, I just threw it open to everyone and said, “It’s your trip. What do you want to do?”

    Folks said later that in decades of group travel, they’d never seen the like.

    Basically, that’s what Col. Goldstein, Col. Madden, and the GPS Wing did. Just threw it open. “It’s your signal. What do you want to do?”

    The most likely solution may involve a partial adjustment to the signal, and then setting it useable with the caveat that it will not perform to the same degree of accuracy as other satellites, nor uniformly for all receivers.

    Javad Ashjaee of JAVAD GNSS had an interesting suggestion, which basically amounted to what my teenagers sometimes tell me: “Deal.” That is, just turn it on, and away we go. Use the anomaly to study multipath phenomena. Of course, he is in the enviable postion of having, or producing, receivers that can separate out the so-called defined multipath element.

    However it pans out, I commend the GPS Wing for taking such an open, public, and when you come right down to it, honest approach. I  heard a bit of grumbling behind the scenes that some protocols were not adhered to in going so public. But you know what? That’s how things get done, as opposed to bogging down under cover.

    And that Kili thing. We did make it up the mountain. Some of us. Sick as all getout from the altitude. Glad to come down. But we made it. Same’s gonna happen with this SVN.

  • The View From Here: Mapping Harmony

    By Glen Gibbons

    The Global Positioning System has provided more than a few ironies in its relatively short existence: A system so accurate that, until last year, government policy required operators to degrade the quality of the open C/A-code signal. A navigation instrument more accurate than the maps across which navigators plotted their courses. Early GPS-based car guidance systems that displayed vehicle location in the middle of buildings or lakes.

    But, as with so many other aspects of daily life, what may have seemed funny before September 11 is no longer a laughing matter..

    The need for a better correspondence of location information is underscored by the urgency being given to the Federal Communications Commission’s (FCC’s) five-year-old mandate for enhanced 911 (E911) services. E911 provides mobile telephone users with the same automatic location information (ALI) of emergency calls now en-joyed by users of wireline phones at fixed sites. The benefits of ALI for getting police, firefighters, and ambulances to an emergency quickly are obvious..

    The first phase of E911 implementation — identifying the nearest cell site from which a call comes — only covers less than half of the U.S. population. Implementation of Phase II, which requires much more accurate real-time positioning, was scheduled to begin October 1. Last month, however, the FCC granted extensions to five national wireless carriers for initiating their Phase II plans. The agency still expects carriers to provide all mobile phone users with E911 coverage by the end of 2005..

    Three wireless carriers will employ handset-based assisted-GPS techniques in providing ALI that must be twice as accurate (50 meters versus 100 meters) as the “network-based” positioning that the other carriers have selected. (This should prove interesting in the marketplace. Because the E911 capability imposes no direct cost on customers, why would consumers choose non-GPS equipment and carriers offering substantially less accurate service?).

    Little of the E911 delay stems from unavailability of GPS technology. Upgrading software at switching servers is the primary cause for postponements sought for handset-based systems. Even with the lower accuracy standards, however, carriers with network-based solutions pleaded for more time to get their positioning technology to work..

    After the communications and positioning kinks are worked out of the E911 systems, public safety and commercial location-based service providers will still face an operational dilemma. That is the mismatch between positioning techniques and mapbases and differences among maps discussed earlier. Cartographers have long understood that variations among coordinate systems and datums can make the same latitude/longitude mean different things to different people. But until GPS came along, navigation and tracking techniques were so much cruder that such cartographic variations disappeared inside the error ellipse of the positioning systems..

    Under Phase II, emergency call centers (public safety answering points or PSAPs, in FCC parlance), public safety agencies, and E911 callers need to be on the same page. Use of proprietary mapbases with incompatible grid designs in either paper or electronic format is a recipe for disaster. It will create coverage ambiguities near PSAP boundaries (Which agency should handle the call?) and lead rescuers tens or even hundreds of meters away from injured or imperiled callers. Yet a distinctive reference grid seems like a much less important proprietary feature for competing map vendors than the other information and cartographic design built into their products..

    The Public X-Y Mapping Project has proposed one solution to this mishmash of maps: adoption of a U.S. National Grid (USNG) for Spatial Addressing. The USNG would effectively match up with the Military Grid Reference System (MGRS), taking advantage of that public domain systemyy?s use of the Universal Transverse Mercator (UTM) grid. MGRS is one of the most common datums residing within GPS receivers and could be made the default mode for E911 calls, according to Jules McNeff, one of the mapping project’s principals and a well-known GPS advocate.

    Agreement between civilian and military mapping standards in these days of homeland security concerns probably wouldn’t be a bad idea. And the benefits, of course, would carry over into the commercial realm of value-added location-based services, too..

    The interagency Federal Geographic Data Committee’s standards working group recently recommended adoption of USNG as a preferred national standard. “Effective implementation of USNG on maps and in GPS receivers is the single most important thing [that we] can do to improve emergency response operations nationwide almost immediately,” says McNeff. Readers interested in exploring the USNG proposal can find more details on-line at and.

    Whether it’s USNG or another universal reference system, GPS manufacturers, public safety agencies, commercial service providers, mapmakers, and the general public have a common interest in achieving a GPS-friendly national spatial standard.

  • Apocalypse 911

    By Glen Gibbons

    “Limited only by our imaginations.”

    People like to say that about uses of GPS, or what some-one would do if they won the lottery, or a child’s options when released from school into an endless summer.

    But sometimes it’s good for our imagination to have limits. Some things our hearts and minds are better off not being able to visualize.

    Consider our recent horrors. Nazi death camps. Hiroshima. Cambodia’s killing fields. Genocidal Tutsis and Hutus. And now the twin towers of the World Trade Center. The Pentagon in flames, for crying out loud!

    One moment, an idea was unimaginable; the next, it’s historical fact — indelible, inescapable, unforgettable. The world has changed, and we along with it. The new millennium has cut its teeth on the edge of a sword.

    Probably John of Patmos would have preferred not to have had his imagination stoked by revelation 2,000 years ago. Yet there it was: the fourth seal, a pale horse and rider, his companions loose in the world, wielding death by sword, famine, pestilence, and wild beasts. Four horsemen, but riding under a single banner of terror.

    Many must feel the apocalypse is bearing down on us now, like the planes bearing down on those three buildings in New York and Washington. Even the date has an ominous numerological coincidence: September 11, 9-11, the same numbers that were punched frantically into cell phones as events rushed toward their horrible destiny.

    So, we find ourselves as though on the edge of a precipice, crevasses opening ahead of and behind us: irrevocably separated from what now seems a sweetly peaceful past, the way forward blocked by an abyss of certain dangers and uncertain risks.

    The already stuttering economy has mimicked those tumbling structures in New York and Washington, although the collapse has been nowhere near as devastating or profound. We have gone down into a valley – emotionally, economically – and it may be a long way till we climb back out.

    In this long journey back to the light, however, I expect that we will find GPS has become more a part of the recovery than a victim of the decline. Why? Because it is such a fine tool.

    In the present circumstances, of course, the first uses of GPS that come to mind are the military ones. The guided missiles, the handheld and vehicle-mounted navigators, GPS/wireless locators for downed pilots, precision munitions like those discussed in an article elsewhere in this issue. Yet even as an aroused world tries to extricate the sources and agents of terror from a global body politic, we will find broader uses for GPS.

    The Volpe Transportation Systems Center report on the vulnerability of transportation infrastructures relying on GPS, released the day before the terrorist attacks, will evoke even stronger resonance now. Security has become the watchword not merely for a day, but for the foreseeable future.

    Consequently, we’ll see a lot more GPS surveying, mapping, and machine control systems at work in securing physical assets. We’ll see increased efforts to ensure the use of GPS timing that underlies the world’s synchronized telecommunications infrastructure, the Internet, power systems, local and wide area computing networks. We may even see some innovations in emergency automatic landing of aircraft seized by hijackers, as discussed in an essay in this issue.

    But I suspect that the biggest incentive that these tragic events will provoke in GPS applications will be in its use in tracking people and assets. Figuratively reaching out and touching someone, as the well-known wireless marketing slogan puts it, is no longer enough. To more completely assuage the anxious undercurrents that these events have set in motion, we’ll need to be able to reach out and locate someone, or let someone know our own location. So, too, our public modes of transportation, our material goods in transit, will demand even greater real-time knowledge of their location and status.

    Yes, a chasm has opened before us. And yet, to come safely across to the other side, it doesn’t matter how deep the abyss is, but rather how wide. Our actions in the months and years ahead can widen or narrow the gap separating the world from a better future. In that regard, we should consider the words of German philosopher Friedrich Nietzsche, “He who fights with monsters might take care so that he doesn’t thereby become a monster. If you gaze long into an abyss, the abyss gazes also into you.”

    The United States has been grievously injured, innocent people wrongfully killed. Yet every nation has some cause to cry out for justice; every human being has a right to be delivered. To navigate this perilous terrain, will require better guidance than even that available from GPS.