From mujibur.inmind.com!uunet!in2.uu.net!newsfeed.internetmci.com!news.msfc.nasa.gov!bcm.tmc.edu!newsfeed.rice.edu!news.sesqui.net!news.concom.com!news Wed Aug 9 10:25:27 1995 Path: mujibur.inmind.com!uunet!in2.uu.net!newsfeed.internetmci.com!news.msfc.nasa.gov!bcm.tmc.edu!newsfeed.rice.edu!news.sesqui.net!news.concom.com!news From: green@concom.com (Chris & Kathy Green) Newsgroups: sci.geo.satellite-nav Subject: Magazine Review of 4 GPS Units (Mag Text) Date: Tue, 08 Aug 1995 06:39:07 GMT Organization: Connections.com, Inc. Lines: 260 Message-ID: <40715l$coi@carbon.concom.com> Reply-To: green@concom.com NNTP-Posting-Host: dial200.concom.com X-Newsreader: Forte Free Agent v0.55 This is the review portion of an article which appears in the August 1995 issue of Outdoor Action magazine. All written material which follows is copyrighted by Outdoor Action magazine. I am posting this as an aid to anyone looking for a handheld GPS and I have no intention of infringing on anyone's copyright. GPS Navigation Know where you are -- anywhere on earth...... by Scott Stoddard [ Intro about GPS basics removed for brevity] Using a handheld receiver -- We borrowed four GPS units from various manufacturers to write this article, and found all four relatively easy to operate. Most of the units come with a minimum of buttons and require a few minutes with the instruction booklet to figure out how to run all the functions. If you're the type that can't program a VCR, don't let the flow charts and thick instruction manuals fool you -- it doesn't take a rocket scientist to do GPS. In fact, all the math, trigonometry, measurements, and timing are processed automatically by the receiver. It's often just a matter of turning the unit on and letting it gather data for a few minutes before you come up with a current fix. All receivers however, require an initialization process called "cold start." New receivers require cold start after you install the batteries. Older units that have had the batteries removed for long periods will also require cold start. Cold start takes anywhere from 15 to 45 minutes and is the process whereby the receiver downloads information needed to begin processing navigation fixes and solutions. During the initialization process, an "almanac" is collected by the receiver that contains information concerning satellite orbit and the parameters needed to compute elevation and azimuth angles. Unless you remove the batteries for longer than an emergency capacitor can hold a charge, the almanac will remain stored in memory, and will help the receiver begin immediately to calculate positions each time you turn on the unit. Most of the GPS units we tested had similar features. Satellite signal strength was best shown using bar graphs, and satellite position was easily shown by those using a graphical format using two circles for the sky and numbers for individual satellites. The outer circle generally depicts the horizon while the inner circle represents 40 to 45 degrees above the horizon. The dot in the middle of both circles represents 90 degrees (straight up overhead). North is at the top of the screen. The satellite position screen is important because at various times during the course of the day, satellites may become aligned in a row instead of being distributed somewhat randomly overhead. The geometry involved in this distribution will afect the accuracy of a reading. Some receivers will indicate poor satellite alignment and suggest waiting a while before taking a reading. Other important menu items include setup options for programming GPS operations. Be sure to find the "update rates' option, especially if you have a new receiver. This command will let you determine how often you want the receiver to make position calculations. Battery life will dramatically increase if you go from a one-second update rate to a five-second rate. Other important items to program are: screen contrast, automatic shutoff, multiple-key turn on, screen light, distance units, elevation units, speed units and clock style. Time adjustment lets you choose UTC (Universal Transverse Mercator). UTM is generally found on all land-based maps and quad sheets. After you learn how to acquire your current position, you'll want to learn how to enter landmarks and name them. Entering landmarks is usually quite easy. With the Garmin 40 and Trimble ScoutMaster you simply press one button. With the Magellan Trailblazer you press the enter button three times, and with the Eagle AccuNav you press the WPT button twice. Naming landmarks takes a little longer. Each receiver has cursor keys that point right and left and up and down. With these keys you must cursor through the alphabet one letter at a time to spell out a word, and then press enter to store the name in memory. Once you have a list of waypoints, you can enter them as a "route" for returning back to camp, or for future trips to the same location. For example, I've spent many nights camping in the Mojave desert of California. On one trip I ended up camping in a different spot, hidden up a wash I normally don't camp in. After a few hours of hiking and riding around the area it was time to go back to camp. Only problem -- I couldn't find the spot. I wasn't really lost because I knew exactly where I was, landmarks such as a large dry lake bed, highway ribbon five miles to the south, two sets of mountain ridges -- one distinctly to the west and one the east. However, all sagebrush looks alike, and the same with all dry washes. I just couldn't find the right wash to head up into. Even after climbing surrounding peaks and backtracking up and down the dirt road I couldn't find it. It was only after I decided to look for the tire tracks leading off to camp, that I found my Jeep, water and food. With four GPS units to test, I purposely did the same thing, camping in a nondescript place -- only this time I metered my camping spot as a landmark in memory of the Magellan Trailblazer GPS. Later after exploring the area for a few hours I tried to find the spot on my own and ended up a half mile further east than I wanted to be. I could determine this simply by turning on the Magellan Trailblazer and pressing the GOTO button twice and then cursoring down the landmark list to "camp." After I pressed enter, a display screen showed me which direction I needed to travel to go back to camp, and how far away I was. As I approached 50 feet from camp the display read "close" and when I was within 15 feet of my Jeep the display read "arrived." All four receivers we tested have the same navigational functions that let you steer a course back to a landmark. While distances and coordinates are precise to within 300 feet, the elevation accuracy leaves something to be desired. On a trip to the Sequoia National Forest on the Kern river we tested all four units for elevation and found them off by as much as 500 feet. Our campsite was acutally 2,320 feet above sea level and the best reading of the day was with the Trimble ScoutMaster showing us at 2300 feet. Later, hiking up to a hilltop at 2,593 feet according to our topo map, the Trimble showed us at 3,100 feet. Comparing the Units -- Of the four GPS receivers we tested, the Eagle AccuNav Sport was the largest, measuring a full 10.5 inches with the antenna extended (7.8 inches closed). It was also the heaviest, weighing in at 22 ounces. While size and weight might be troublesome to ounce-counting backpackers, the trade-off is worth it because you'll be getting one of the best performers of the four. The AccuNav is the only unit we tested with a five channel receiver. Multiple channels provide for faster satellite acquisition, especially in tough areas where trees or hillsides block signals. On our river trip to the Kern the AccuNav was the first unit to come up with the fix of our camp located next to the river, 1,000 feet lower than the surrounding hills. The AccuNav was favored by many of our crew for being simple to operate. It's almost like the instruction manual is inside the unit -- with its 15 buttons (besides cursor keys) and numerous screen menus, you don't have to study for 30 minutes just to learn how to turn it on. The plotter function is truly amazing. As you walk along it will draw a line showing your path and the direction of travel. The display backlight is on of the brightest available, and the LCD screen -- one of the largest available. Note that coordinates for seconds in logitude and latitude are given in thousandths of minutes. The Trimble and Garmin units do the same. This method may be more accurate for determining locations, but for those used to Magellan receivers with the traditional two numeral places for seconds -- you'll have to do a little math to convert back and forth. The Garmin GPS 40 was the smallest unit tested, measuring only 6.1 inches high and two inches wide. This size allows for one-handed operation. The keypad includes seven operating buttons with a two-speed thumbkey cursor button for all four directions. The Garmin's size will endear it to backpackers the most, and its well thought out menu sequences called pages take no time to learn. The GPS 40 has a very large LCD screen for tis size, and displays both satellite positions and signal strength in one screen. Instead of a plotter there is a "moving map" that you can zoom in and out of th see the landmarks you have entered. The GOTO function of the Garmin is similar to the steering guidance graphic of the Eagle. A perspective road leads off into the distance and turns to the right or left when you get off track. Weighing in at only 9.4 ounces, the Garmin is probably the best choice for serious, weight-conscious backpackers and hikers. One of the first units we were able to try was the Magellan Trailblazer XL. It was the only unit we tested that features a swivel-up quad-helix (quadrifilar) antenna instead of the flat "patch" antennas most companies use. The quad-helix is said to have better GPS signal receiption but most companies don't use it because it makes package design more difficult and less sleek. The XL features an 11 button keypad that is easy to operate, even with gloves on. Main functions like navigation and GOTO can be operated with very few button punches. Since this was the first unit I tried, I got used to the menu functions and screens, and favor the simple operating system it uses. While other units seemed to work better in the river bottom of the Kern, I still prefer using the Magellan in wide open country like the desert. One of the top selling features of the Trimble ScoutMaster GPS is its "Over and Up" function. Over and up lets you find your current position on a map by measuring "over and up" from any reference point you have entered into memory -- usually a spot on the edge of the map with coordinates already given. Once the GPS has determined your current location, Over an Up will tell you how many inches west and how many inches north to measure to find your position on the map. For some reason we couldn't get Over and Up to work with our Kern River map, but trying it out again with a topo of Anaheim and Placentia produced successful results. How close was the accuracy? The reading said we were about 100 yareds west of our true position. The Trimble ScoutMaster offers one of the smallest LCD screens of the lot, and except for small symbols, lacks graphics for better user interface. It does offer a three-channel receiver for faster updates and satellite acquisition, but plan on some serious study time to learn the menus and button functions of the ScoutMaster. The instruction manual is 140 pages long. The price of the ScoutMaster is almost double that of all other receivers we tested at $995 -- another big negative. While a computer interface might be the redeeming feature of this unit, you'll pay another $400 for the software and data I/O cables required. All of the GPS receivers we tested perform with an amazing accuracy that was almost unheard of until a few years ago. They probably provide many more functions that the average person will ever need but it's nice knowing they have these extra capabilities. Choosing one over the other is more ofa personal preference -- finding the one you feel most comfortable with. Remember, GPS is a tool and not a cure-all for getting lost. While traditional outdoorsmen may even doubt its usefulness, skillful travelers who recognize GPS' potential will discover unique and clever applications for its use in the wild. THE END. GPS Comparison Chart Eagle Garmin Magellan Trimble AccuNav Sport GPS 40 Trailblazer XL ScoutMaster Dim. 7.8"Hx3.6"W 6.15"Hx2"W 6.125"Hx3.5"W 6.8"Hx3.3"W x1.7"D x1.23"D x1.25"D x1.3"D Wt. 1 lb 4 ounces 9.4 ounces 14.7 ounces 14.7 ounces Chan. 5 1 1 3 Batt. 6 AA 4 AA 3 AA 4 AA Batt N/A 10 hours 5 hours 6 hours Life Input 6-35V DC 5-40V 11-16V DC 10-32V DC Volts Water Yes Yes Yes Yes proof Nitro Yes Yes No Yes Filled Update 1/sec 1/sec 1/sec 1.5/sec Rate Acqui 2 mins 2 mins 2 mins 2 mins time Screen 2.25" x 2.25" 2.2" x 1.5" 1.875" x 2.25" .875" x 2.12" Size Sugg $499 $499 $499 $995 Retail GPS Manufacturers Eagle AccuNav Sport Eagle Electronics P.O. Box 669 Catoosa, OK 74015 (800)932-4534 Garmin 9875 Widmer Road Lenexa, KS 66215 (913)599-1515 Magellan Systems 960 Overland Court San Dimas, CA 91773 (909)394-5000 Trimble Navigation 9020-II Capital of Texas Highway North Suite 400 Austin, TX 78759 (800)959-9587 Chris Green cgreen@concom.com