Pacific Connection(英語)

Navigating the Backcountry with a GPS

For a while now, I've been obsessed by a palm-size, wireless device that receives useful data from anywhere in the world. No, it's not a personal digital assistant or a cell phone. My favorite gadget these days is a global positing system, or GPS---a sort of homing pigeon for your pocket that can get you through mountains, deserts, snow fields, savannahs and oceans. Seemingly overnight, the GPS has turned the trusty compass into a mere backup device.

GPSs do essentially one thing: determine where in the world you are within about a hundred feet or less. Global positioning systems are the ultimate answer to the problems of navigation that have challenged everyone from the Polynesians to Captain Cook. That even the lowest-end GPS can do this with extreme accuracy is due to a $10 billion U.S. military project that put 24 satellites in orbit, all tracked and synchronized by ground stations. When a GPS is activated, it downloads or updates an "almanac" of orbit information that includes the location of each satellite. By receiving a known number sequence from three of the satellites, a GPS can determine its distance from each---then triangulate the results to determine your position. Add data from a fourth satellite, and the device makes a credible estimate of your altitude.

GPS accuracy improved after a Clinton administration decision to stop broadcast of the Selective Availability signal, which intentionally degraded accuracy. Overnight, GPSs that could only find the parking lot could suddenly could locate your car---or at least get you close. An earlier advance, called multi-channel reception, has also given GPSs a boost by shortening the time required for a unit to "lock" onto a location. The feature was once found only in military models costing $20,000 and up.

GPSs "know" where they are and can remember where they've been or where you want to go. By recording a "waypoint," a fixed latitude/longitude position, you can tell the distance and direction from your current position to that waypoint. You can store a waypoint onsite, say at the beginning of a trailhead. Or you can determine waypoints ahead of time using online maps---which I do with the help of an Australian software package (more on that in a moment). Either way, waypoints are invaluable for navigating the world without getting lost.

I have proved the technology's worth to my satisfaction innumerable times in the car, on foot, on sailboats, and once, on bicycle while visiting friends in Holland. Weiger and Diane live in a semi-rural, bicycle-friendly area an hour by train from Amsterdam. One morning I borrowed Weiger's bike, took a waypoint of their house, then pedaled through the maze of streets as randomly as possible.. An hour later, I turned the GPS back on and used it for a guide. At every turn, the GPSs arrow pointed the direction to their home, while a kilometer reading showed the remaining distance. At .3 Km, I was back in their neighborhood. At .2 Km, I was on their block. And at a reading of nearly zero, I was standing in front of their house. So ended my long career of getting lost---including one time in Gstaad, Switzerland where a walk for a morning croissant required the services of an English-speaking cab driver to get back. These days in unfamiliar places, I can wander recklessly, then turn on the GPS when I'm ready to return. My GPS has helped me find companies in strange cities, rental car return lot at airports, and most recently, the big Central Library in downtown Los Angeles.

Indeed, the most popular use of GPSs is---or soon will be---for automobile navigation on city streets. Here, Japan, as usual, is leading the way as in-car GPSs are rapidly growing in popularity. Some Americans, too, are testing the technology in rental cars, or as an option in some high-end automobiles. But for the most part, we are still asking directions. (Well, American women are asking directions; American men would rather stay lost.) In the U.S., GPSs' pioneering users are not city drivers, but hunters, skiers, bicyclists, drivers of off-road vehicle, snowmobilers, mariners, and hang-gliders, as well as hikers like me. In many ways, these constituencies have little in common, and in the U.S., they fight continually over land use. But for better or worse, the global positioning system serves us all.

Locating waypoints in advance

When Americans go outdoors, they sometimes take highly detailed topographical ("topo") maps produced by the United States Geological Survey. Sold at outdoor supply stores and directly by the U.S. government, topo maps give a detailed portrait of the landscape, with elevation lines and many trails. The most precise topo maps are printed at 1:24,000 scale, or two inches to the mile, spanning 7.5 minutes of latitude and longitude. With the help of a compass, a skilled map reader can use distant peaks to triangulate an approximate position. With a GPS readout of your current coordinates, you can also interpolate your position using the map's grid. But there's a better way---more convenient and exact---in which you mark waypoints on a digitized map in advance of your trip, download those waypoints to the GPS, and use them in conjunction with a map you print out at home.

For many countries, the best way to get a digitized map is to scan one in. In the U.S., you can also purchase maps on CD-ROM. National Geographic is the best-known source with its Topo! packages, which "stitch" several maps together into a easy-to-use continuum. But there's an alternative, one that is less convenient, but much less expensive. U.S. topographical maps are not copyrighted and can be found, for free, on the Web. The website www.gisdatadepot has amassed the Internet's largest collection of free topographical maps from throughout the U.S., all in .TIF format. (As far as I can determine, comparable digitized maps are not, at least yet, available online for Japan. )

Once a digitized map is obtained, it must be "georeferenced." A georeferenced map is one in which every pixel has been mapped to a latitude/longitude coordinate, so that every mouse position has a corresponding coordinate. Most online maps already come georeferenced. Others, including maps you scan yourself, can be georeferenced with the appropriate software: you mark at least two (preferably more) known waypoints, and the package interpolates the rest.

That's where my Australian shareware package comes in. OziExplorer ("Ozi" is slang for "Aussi," as in Australian.) is coded and maintained by Des Newman, while his wife, Lorraine, produces the package's graphics and is his business partner. The Newmans provide a limited trial version from their website ( A $75 registration fee activates the disabled features. Compared to more mainstream packages, OziExplorer is a bit rough around the edges, but the package's help menu imparts a sense of camaraderie that harkens back to an earlier era when personal computing was truly personal. "I have tried to make OziExplorer as user friendly as possible," writes Newman in the "Getting Started" section, "but mapping is a very complex subject and there are many things you must know..." Newman invites users to write him with their concerns and has made extensive changes from user suggestions. While the source code isn't open, the API and waypoint formats are fully documented. Users can also avail themselves of a friendly OziExplorer discussion group hosted by Yahoo!.

A hobby turns into a business

As with many good packages, Newman first developed OziExplorer for his personal use, to map four-wheel drive trips through the Australian outback, the vast interior region of Australia. "I bought my first GPS and wrote OziExplorer because on one trip (without a GPS) the roads did not appear to be where I thought they should have been," Newman wrote in an e-mail correspondence. "A GPS and laptop with a moving map running would certainly have made that trip easier."

To develop the program, Newman taught himself about mapping, "reading everything that looked useful I could find on the subject." He began coding OziExplorer in April 1997, writing in Delphi 3. He produced his first beta ready for downloading in three months and made his first sale that September. "It was a crude program only supporting Lowrance receivers (which was the GPS I purchased), and of very limited capability," Newman wrote. But at the time, there was nothing else quite like it. And except for one competitor, there still isn't.

These days, Newman scans in the relevant map, works out where he wants to go, and, using OziExplorer, places waypoints on all the road and track intersections, towns, and other landmarks. He adds annotated comments where appropriate, as well as "events"---non-waypoint points that could embody a photo or notes. When he's satisfied, he prints out the map and downloads the waypoints to his GPS. Hence in one of earth's most unpopulated regions, Newman knows exactly where he is at all times---which is a big source of comfort when you're a hundred miles from nowhere. "There has not been a place I would not have gotten to without OziExplorer, but it gives you a peace of mind and allows you to concentrate on other issues."

Newman has continued to enhance OziExplorer, and now the package's growing popularity is threatening to turn the hobby into a full-time business. "Development is starting to suffer so sometime in the near future I will have to make a decision about my full-time job," Newman writes, referring to his career as an IT professional.

Meanwhile, OziExplorer has brought other rewards besides financial ones. Among serious GPS aficionados, Newman has achieved wizard status. He often meets users in his travels through Australia, and had made many acquaintances through email. And he has the pleasure of hearing about unusual applications for the program. "One chap uses OziExplorer with scanned maps of a road construction site. He has written a program using the OziExplorer API which calculates distances from waypoints he has set up on the chainage markers. He can then navigate along the job and know his approximate location (the chainage) at all times."

OziExplorer goes to Texas

Here in America, the closest thing we have to the Australian outback is the region known as the Southwest: Arizona, New Mexico southern Utah, and west Texas. To put OziExplorer through its paces, I took my Garmin eTrex Legend GPS and a folder full of maps prepared with Des Newman's program, and flew to El Paso. After a seven hour drive, including a Mexican lunch in Marfa, Texas (the location for the James Dean film Giant), I arrived at Big Bend National Park.

Well, it wasn't quite that easy. Big Bend, named for a giant curve of the Rio Grand river, is a big park, requiring a download of 21 7.5 minute top maps, and one "15 minute" map for reference---all from Even with a broadband connection, this took some time because these are large TIF files ranging from 4.4 to 7.2 MB. Moreover, the site limits data speeds and simultaneous connections for non-subscribers. Not that I'm complaining. The comparable hardcopy maps would have been difficult to obtain and cost over $100. Indeed, the combination of OziExplorer and the free data is as close as you can get to an open source GPS mapping solution. Once I had the maps on my hard disk, georeferencing proved easy because of OziExplorer's export feature for the United States Geological Survey's Digital Raster Graphic (DRG) format.

With the georeferenced maps on disk, I could plan my hikes. I used suggestions from Big Bend's own well-prepared website (, located the appropriate trail on the topos, and marked some waypoints, clicking the mouse at each spot on the trail. To help with precision, OziExplorer provides a virtual magnifying glass showing the precise spot you're marking. Like Newman, I marked all the intersections, but for good measure, I also marked many points in between, just for the pleasure of knowing exactly where I was on the map. I wound up with about 180 waypoints for the trip including some I marked on the spot; my GPS could have handled up to 500. OziExplorer stores all waypoints for a given trip in a separate file, an approach I first considered awkward. But I soon realized the advantage: all my Big Bend maps could employ a single set of waypoints. Update the set on one map, and the edits carry through to all of them.

One of the biggest advantages of digitized maps is the ability to print out customized versions for the trip at hand. OziExplorer offers several print options: you can print out the entire map, the portion you see on the screen, or a selected portion. You can print on a single page or multiple ones. And with hardcopy, the uncompressed TIF format pays off. Even extremely magnified portions of the data printed with surprising clarity. I typically enlarged the portions I was interested in to print on a single page, or in one case, on two pages taped together.

With all my work, I was convinced I carried the most detailed hiking maps of any visitor to the park. Each map was small enough to fit in my front pocket, yet provided extreme detail. I used the GPS to locate waypoints, then located those waypoints on the map. As a result, I knew almost exactly where I was every step along the way. Indeed, the accuracy of my waypoints was beyond anything I expected. The GPS might estimate I was a few hundred feet from a trail intersection. As I kept walking, the numbers counted down, and then, around a corner, would invariably be the trail sign marking the cross-roads, right where it was supposed to be. In almost every case, the accuracy was within 150 feet. Alternatively, I could have also purchased Garmin's topographic software and gotten a "moving map" image on the monochrome LCD display. I may try that eventually, although the printouts I carried are much clearer and more detailed than any display on the market.

The GPS/OziExplorer combination is also handy for marking where you've been. The longest hike I took during our eight-day stay ranged from The Basin, a valley in the lightly wooded Chisos Mountains; along the flanks of Emory Peak, the tallest in the park; to the South Ridge, which overlooks the hot, cactus-laden desert 2000 feet below. During the 13 mile hike, the GPS created a "track"--- a succession of waypoints marking where I had gone. At the end of the day, I stored the track, and, back at home, uploaded the track to the map via OziExplorer. The track almost exactly coincided with the map' printed trail, as well showing where I had intentionally left the trail and hiked "cross-country." If I had been more daring, I could have done an entire cross-country hike with this setup. Indeed, I had plotted such a trip to a spring sitting in the middle of nowhere. But I chickened out, discouraged by 95 degree temperatures in the afternoon shade, the presence of four different kinds of rattlesnakes, the death of a visitor climbing a peak the week before our visit, and the lack of a hiking companion crazy enough to join me. (My wife has better sense.) Still, OziExplorer begs for cross-country exploring and I may venture out yet.

OziExplorer has other useful features. If you enter a track, the program will estimate the distance. If you take digital photos of your trip, you can embed them on the map at the appropriate location. (Newman writes that this feature was a design requirement of Lorraine's.) Newman has introduced a separate Windows CE version of the program that, when used in conjunction with a GPS, enables you to track your position in real-time. As the owner of two CE devices, I considered this option, but decided the setup was too complex for hiking, though I'm tempted to try it for city driving. The combination might be ideal for navigating through Tokyo-which for a gaijin like me is an unfathomable wilderness. In any case, the next time I visit Japan, my GPS will be the first item I pack.

A Software Developer Collects Minerals, Waypoints and Digitized Maps

You never know where a hobby will take you. Alan Robb, a computer systems engineer for Lawrence Berkeley National Laboratory, collects fluorescent minerals: rocks that glow in the light of a fluorescent lamp. Some of the best places to hunt them are in abandoned mines located on vast acres of property owned by the U.S. Bureau of Land Management. Talk about a prescription for getting lost. "You go into mines in the middle of the night, running around in the dark with a fluorescent lamp," Robb says. "If you survive, you come back with something---sometimes."

To find his way around, Robb needed waypoints, and so he obtained a DOS-format database from the U.S. Bureau of Mines, whose data goes back to the 1890s. Robb originally wanted to use the dataset in conjunction with digitized USGS topo maps, because of their wealth of land features. But he was discouraged by the size of the TIFF files.

Instead, Robb used a CD-based program called DeLorme Street Atlas that squeezes a vector street map of the entire U.S. onto a single CD. Writing in C, he created a program to generate Street Atlas files, which superimpose user data---in this case, the mine waypoints--- on the maps. As a result, he can bring up a map that shows mine locations for any part of the United States. "I have a directory of every U.S. county in a tree format. Double click on one, and it brings up the county and the locations of all the mines and quarries in the area." Even though Street Atlas is designed for streets and highways, Robb says the program is surprisingly accurate for the back country. "I don't know where DeLorme got their data, but the map even shows little dirt roads in mining areas abandoned 50 years ago---some so small you can miss them even in the middle of the day.

In his sports utility vehicle, Robb keeps a GPS attached to a laptop with the map CD---a combination that produces a full-screen, multi-color "moving map" that shows his location in real time. Also on the map: waypoints to help with navigation. The same waypoints are also loaded onto a second GPS which he can take with him on foot.

Robb has also amassed a vast collection of digitized 7.5 minute topo maps covering the western United States, which are stored on approximately a thousand CDs. Gathering these maps was mostly a matter of hours devoted to downloading. But in California, Robb's home state, the maps presented an additional glitch. For the rest of the U.S., the topo maps came georefereneced to a standard coordinate system projection called Universal Transverse Mercator (UTM). UTM is popular because it employs the metric system, rather than the more awkward system of degrees, minutes and seconds. But for complicated reasons, California maps employed the Albers projection, which Robb says is one of the poorest for displaying with a UTM viewer. So he wrote a program to re-project the California maps from Alpers to UTM---converting about 3,000 maps. "The code wasn't all that bad once I understood the projection theory," he recalls. He wrote the reprojected maps, about 35 GB worth of data, onto about 80 CDs.

But these topo maps usually stay home, Robb preferring to rely on Street Atlas, whose vector format allows it to reside on a single CD. "My trips usually involve stops at 3 or more sites as much as 500 miles apart; therefore, ease of use has become very important to me," he says. "But if you get very far away from the roads, OziExplorer is the only choice." Robb notes that while vectorization has already become the standard for street maps, outdoor applications will take much longer. "What's missing from the vector topos are the geographic objects---including structures and survey benchmarks." Robb says.

Robb says that, as far as GPS mapping has come, it still has far to go. He notes that the USGS has done little on its own website to propagate digital maps, even though the information, paid for by U.S. taxpayers, is in the public domain. Nor have vendors settled on a single format for importing and exporting waypoints from ASCII files. Robb also criticizes DeLorme for not implementing an import/export interface among its own mapping products.

Ironically, Robb doesn't have much time these days to use all the waypoint and mapping data he has collected. These days, he sees more computer screens than abandoned mines, and he sometimes wonders if the time he spent amassing all this data was worth it. Perhaps his data collection was an acute case of programmers' obsession: the glory of data manipulation for its own sake.