GPS Navigator Magazine : Applying the features to practical applications How to use GPS

Navigation 103, Applying the features to practical applications

How to use GPS

If you’re like us, as much as you enjoy high tech stuff, the VCR still blinks 12:00. God forbid you actually take the time to read the instructions, who has time for that? Do yourself the favor of taking the time to read up on your equipment enough to comfortably know how to use it. Trust us, the first time your trusty GPS unit saves your arse from being hopefully lost, trip ruined, and humiliated in front of your pals, you will thank God, yourself, and maybe us too? Again here are the basics.

Getting a Fix

GPS units are referred to as receivers because that is what they do, receive satellite radio signals. Unlike other types of signals, GPS works on line of site. This means the receiver’s antenna must have a clear view sky to work properly. The good news is that it will work at night, in fog, in a blizzard, or any other extreme weather conditions. Anything overhead, however can limit or block out the signals. This includes heavy vegetation, buildings, or steep cliff walls. If operating in a dense forest or jungle, a clearing may have to be found to obtain a stronger reading.

Out of the 24 orbiting satellites, 12 are in each hemisphere. Receivers need to read at least three at a time to "triangulate" the equipment's exact location. Four are needed to provide a more actuate three-dimensional fix that will provide elevation. The receiver’s Satellite Status Page will show how many satellites are locked in at any given time. It may show the satellites position overhead as well as a bar graph to indicate the signal strength of each. Satellite Geometry refers to how the satellites are positioned overhead. A poor reading may result if the satellites are clumped together in one area or arranged in a straight line. There is a signal strength indicated known as the DOP number. This stands for Dilution of Precision, the smaller the number the better the satellite geometry.

This is good to know in the event the equipment is not working or you question its accuracy. A quick check of the Status Page will let you know the strength of the signals being received as well as if the antenna is working.

The equipment also needs to be initialized. This means the receiver needs to find its position in the world if used for the first time, or if it has traveled a few hundred miles away from its home area with the power shut off. The receiver will usually do this automatically in a minute or two. If not, initialization can take place faster by locating the current position on its electronic map with a cursor, then press Enter. The current position will be indicated by a triangle shaped arrow icon. Cool…there you are, now your ready to go.

Basic Features

OK…now we know where we are. We have good batteries and satellite geometry, its time to take off. Using a special mounting bracket, the receiver is attached to the handlebars of our mountain bike, ready to hit some prime single track trails. With the unit on the Map Page, we see the arrow icon in the middle of the screen pointing to the direction traveled. The trail does not show up on the base map but you notice that dots are appearing where we traveled. This is the electronic bread-crumb trail. These dots indicate the exact previous position traveled. Pretty tough to get lost as long as the unit stays on, because you can always backtrack to the way you came. This method works best when there is another power source other than the only four AA batteries brought along. That is why waypoints are saved which will be explained later.

Still checking out the screen on the Map Page, we notice a couple of other indicators, speed and time of day. It’s nice to know how fast you’re traveling, a luxury on a mountain bike and it helps maintain the pace. A brief stop provides an opportunity to check out the other information the receiver provides. Scrolling through the pages there is a Position Page that tells you the following:

Indicator Status What it means

Compass NW 323° Traveling NW

Speed 0.0 mph Your stopped

Trip Timer 00:35 Started 35 minutes ago

Altitude 1245 ft Current elevation

Avg Speed 11.2 mph Average speed

Trip Odom 06.01 mi Traveled 6 miles

Sunset 07:35 Dinner time

Coordinates N 43° 45.240’ Latitude

W 122° 28.895’ Longitude

That is a great deal of information we have never had access to before. For this application we use the information to keep track of a number of things:

· Knowing where we have been allows the ability to backtrack to the starting point

· How far we traveled, how fast, and how long it took

· Time of day and even how much time left before it gets dark

Neat stuff but do not spend too much time looking at the screen while riding or driving, or your pals will use the latitude/longitude to tell the paramedics where to find the body. Keep your eyes on the road. Better yet have your passenger learn how to read this information so they can help you. In the scenario of our mountain bike outing, we check the information during rest breaks.

So far so good, now things are get more interesting.

Tip: Most GPS receivers provide a Trip Computer feature. Set the computer before your next trek or race to check out interesting data. This includes Trip Odometer, Average Speed, Trip Timer and Maximum Speed.

Saving Waypoints

Saving and traveling to waypoints is one of the primary functions of using GPS. As previously mentioned, a waypoint is a selected point of interest (POI), a location that is stored in the receiver’s memory. The receiver also provides useful information on the traveling status to and from waypoints. This includes the distance remaining to reach the WP, and the ETA based upon the current speed traveled.

The first waypoint that is usually saved is home. Before leaving the house a trip is taken out to the yard to get a satellite fix. The position arrow icon appears and there you are. Holding down the Enter button on most units will give the option to save a waypoint. A screen appears titled Mark Waypoint, and provides a WP number of 001. Using the rockerpad, letters are selected to change the name to [HOME]. This screen also displays the date the waypoint was created and the exact latitude/longitude of its location. A symbol can also be selected, which for our home we may choose the house symbol that will appear on the electronic map.

Tip: Holding down the ENTER button on most receivers, saves the current location as a MOB waypoint. This is for “Man Overboard.” It is designed for immediately marking the location in emergency situations. Ideal in the event one of your beer swilling passengers slips off the back of the sail boat.

In the case of our mountain bikers, they have loaded up the truck and are heading for the mountains. After almost an hour on the road, they approach the gravel road turn off that takes them to the trailhead. This turn off is tricky to find, especially in the dark, so they decide to save it as a waypoint. After getting a satellite fix, they press Enter and see number 002. This is renamed to [TURN OFF]. After six more miles they reach the trailhead parking area which is saved as [TRAILHEAD].

With the GPS receiver is attached to handle bars, they ride on a familiar trail so after awhile, they decide to shut the unit off to save the batteries. After a few miles they start to get into unfamiliar territory, the trial splits into a fork. They estimate they are a few miles from the trailhead. After turning the GPS on and scrolling to the Map Page they see the TRAILHEAD location they previously saved. Using the rocker keypad they scroll back to the waypoint by placing the cursor on it. An information box pops up to indicate that it is 2.7 miles from their location. This distance is straight as the crow flies, and they estimate that they must have rode nearly three and a half miles to get where they are now. They decide the take the right fork, but before they do they save the intersection as a waypoint named [FORK].

They are now in new territory and taken back by the natural beauty of the old growth forest as the trail runs along a creek. Another mile further they come to a large flat top boulder that overlooks a pool in the creek. It’s a great place so the group decides to stop for lunch and a dip in the water. They dry off basking in the sun on top of their newfound rock. They will want to come back to this place again so they save the location as [SUN ROCK]. After riding a few more miles, they decide to head back.

Traveling to Waypoints

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During the last couple of miles they paid more attention to the scenery than where they were going. They got a little turned around and now question if they are riding in the right direction. They turn on the unit which shows the previously saved SUN ROCK. Pressing the Go-To button provides the opportunity to select a waypoint to travel to. They select SUN ROCK and press Enter. The Map Page screen appears with additional information. They are 2.7 miles away with an estimated time of arrival of 21 minutes based on their current speed. There is also a small arrow pointer indicating which way to go. The Compass Page also indicates they need to travel at a compass bearing of SE 135°. This is a good opportunity to note that it is difficult if not impossible to follow exact degrees during ground travel. This is because one must follow roads or trails and move around obstacles. Following compass degrees in a bearing is more relevant in the air or on the water. Degrees however, are still useful by indicating which general direction to travel.

Note: Unless flying or sailing, compass bearings are difficult to closely follow. Waypoints help shorten straight-line distances to help navigate around large obstacles. This greatly increases the ease of following the actual compass bearing to each waypoint.

They check the battery indicator they decide to leave the receiver on until they reach the SUN ROCK. They follow a path that takes them back in a SE direction until the area looks more familiar and the receiver ticks down the time and distance until they reach their favorite boulder. Checking the receiver again they see the FORK and TRAILHEAD points. Using the cursor again they scroll over the TRIALHEAD to discover that they are 3.9 straight miles away from the truck. They estimate almost five miles to go in actual distance. Knowing where they are and how far they have to go gives the group confidence and allows them to enjoy their trip.

Active Route

A Route is a series of waypoints that are listed in the order of start to finish. Routes may contain up to 30 waypoints depending on the complexity of the route. New routes are titled, then a list of waypoints are selected to be contained within.

There are a few of advantages to using this feature. A route organizes a number of waypoints making navigation easier while reducing the risk of error. Multiple waypoints like Rock, Stump, Bridge, River may not mean a lot by themselves. Routs give them order, making an easy sequence to follow. Routes are also reversible. Once the last waypoint destination is reached, the route is reversed by an Invert command to backtrack to the starting point. They also provide useful information regarding the position of the waypoints. This includes distance and compass bearings between each as well as the total distance for the route.

Our group of mountain bikers created a route of their trip that looked like this:

Title: Westfir Mt Bike

Waypoints Distance Bearing

1. HOME 00 mi 00°

2. TURN OFF 51 mi 99°

3. TRAILHEAD 5.9 mi 12°

4. FORK (Right) 2.7 mi 123°

5. SUN ROCK 1.9 mi 181°

6. END 3.1 mi 90°

Total Distance 64.6 mi

Tip: A short reference line can be saved with each waypoint. On the above FORK waypoint, the direction Right was added. Waypoints can be selected to appear on the receiver’s electronic map by name, symbol and reference.

First Edition Revised December 2000

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