THERE’S MORE TO using a GPS device than setting waypoints and following routes on an electronic map. There are settings to adjust, coordinate systems to learn and procedures to prevent errors. You must be on target 100 percent of the time when navigating. One error is enough to get you lost!
Take this quiz and see how much you know about GPS navigation. Some questions might appear to have more than one right answer. Choose the best answer.
After taking the ‘Positioned for Success: GPS Devices’ quiz, use this list of answers with explanations by the author to check your work.
You must be using old information for GPS questions. Currently available Garmin Units have WAAS accuracy to 5m. Scouts on a trail should have more than one gps unit along with compasses. Training in proper use along the way will go far for future use by scouts.
Yes, most new GPS units have the WAAS option. But, for all its benefits, WAAS has some drawbacks.
1. Coverage is only available in North America.
2 You may not be able to receive signals if trees or mountains obstruct your line of sight to the satellites over the equator. Waas works well on open land and water.
3. Reduced battery life in your GPS.
4. WAAS is a series of geo-synchronous satellites with ground based stations that transmit position corrections based on changing weather patterns. GPS works on the principle of transmitting signals at the speed of light in a vacuum…which works great in outer space. But the Earth has an atmosphere. And in that atmosphere changing weather patterns effect the speed that those signals are transmitted from the satellites. It is critical that the speed correction factor is accurate to the nano-second. So ground based stations monitor the weather and can send correction factors to the geosynchronous satellites which, in turn, send them to your GPS…just like a GPS satellite does. It is a form of differential GPS. The ground based stations are typically found near major airports. If you are not in that weather pattern (basically over 200 miles from the ground station) and WAAS is enabled then you are getting correction signals even though your weather pattern is different. So you are getting ERRORs incorporated into your GPS position.
A normal accuracy of 14 meters or so is plenty accurate for wilderness navigation.
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Q.5 Your GPS unit can determine your position even though there are heavy clouds overhead. But the position doesn’t match up with where you know you’re located. What could be wrong?
a) The GPS unit is always more accurate on a sunny day.
✓b) The GPS unit is getting a two dimensional (2-D) fix, not a 3-D one.
c) The GPS unit isn’t locking onto enough satellites for an accurate fix.
I think the only reason a GPS would use a 2 D fix is that it cannot “see or receive” enough satellites signals. So C seems much BETTER answer.
Good point, Troy. My apology. Give yourself credit for that answer. As you observe, it’s really the same–you’re getting a 2D fix because the satellite can’t access enough satellites.
I take exception to #6 — “You call 911 on your satellite phone and request a medical evacuation. You should give the operator:
a) The UTM coordinates of your position”
Ground search and rescue operations use UTM coordinates to plot locations. Any SAR group that receives Search Team Member, Search Team Leader, or any other position training from the Va. Department of Emergency Management (VDEM) learns and follows this standard. It is more than likely that if there is a medical emergency, SAR teams will be called out to handle the evacuation — unless the person making the call is able to convince someone that an expensive helicopter rescue is necessary and required, in which case lat/lon would be appropriate.
Thank you for the heads-up on this. However, all the bush pilots I’ve flown with operate primarily with latitude/longitude. It’s no biggie though–conversion is easy. There would be a problem, however, if the reported coordinates did not include the zone number.
Here’s another question. Your car GPS has directed you to a cliff, and you just went off the side. The GPS is now saying “recalculating”. What do you do now? Sorry, that is from a cartoon I once read. Seriously, the latest information of GPS can be found at http://www.gps.gov/. It says a high quality GPS receiver can have better than 3.5 meter meter accuracy. The signal used to be “dumbed down” for the accuracy you mention in the quiz- but not anymore. The chart at http://www.gps.gov/systems/gps/performance/accuracy/ shows a usual accuracy of 1 meter.
Yes, if you have WAAS turned on. If not, don’t expect 3.5 meter accuracy. Note from above that it’s not always wise to use WAAS