Back
to school to learn how to use GPS
(Part 1)
By
Jack W. Peters
Welcome and congratulations
on taking the initiative to increase your knowledge of GPS navigation.
Our goal is to provide the relevant and practical information necessary
to get you there and back, making every adventure a successful one.
This means teaching how to tell time more than how the make a clock.
We are not techno-geeks and will not try to write like one.
If interested in the scientific information, there are a number of other
resources which provide the highly technical details. We have covered
the brain numbing technical information for you and have tried to extract
the information that is actually needed.
Studying this information
with your products instruction manual will provide an understanding
of how GPS works, and the equipments many capabilities. It is also
very important to learn how to use a map and compass. Using GPS in
conjunction with a map and compass will substantially increase navigation
skills, allowing GPS receivers to be utilized to their fullest potential.
Practice
will further increase confidence by reducing the chance of becoming
lost.
This is both good and bad
because we will provide enough information to allow you to actually
know what youre doing, which of course will make you dangerous. The
information is also somewhat general, providing examples of what features
are available and their possible application in the field. Every brand
of GPS receiver, (although sharing most of the same features), may work
a little differently. We highly recommend an ongoing study and practice
of your navigation skills, which includes getting out the products
instruction manual and actually reading it.
Now a word from the legal
department: Traveling and navigation are potentially dangerous
activities. This information is not a substitute for reading a GPS
receivers instruction manual. Using GPS can be danger in at least
two regards. Watching the screen instead of the road, and relying on
GPS as the only means of navigation. So keep your eyes open, pay attention
and be responsible enough to understand your equipment and abilities.
Navigation
101, Defense spending pays off for civilians
What GPS is and how it works
GPS,
an acronym for "Global Positioning System," is a U.S.
military technology that has been adopted for civilian use. Twenty-four
orbiting Department of Defense satellites broadcast radio signals that
through a GPS receiver, provides precise coordinate information worldwide.
The system
was first conceptualized in the 1960’s for worldwide U.S. military
navigation. By the mid 1970’s it became a joint effort by various
branches of the U.S. armed services, and was referred to as Navstar.
Despite the official name, it was the term GPS that stuck. The system’s
first major military debut was in 1991 when it contributed to the overwhelming
success of Desert Storm. With the system still in its infancy, only
16 satellites were utilized and were specially located over the Persian Gulf area. Hand held receivers helped allied forces
navigate and maneuver around enemy positions in an unfamiliar desert
without landmarks. The system was considered fully operational in 1995.
Like its "Humvee" cohort, GPS has numerous practical civilian
applications. For more military related information be sure to check
out our section GPS
at War.
U.S. tax
dollars were hard at work as Uncle Sam spent 17 billion to develop this
system and we can use it for free. That’s right, no set up or
monthly fees. Commercial, recreational, friend and foe alike, anyone
with a GPS receiver can access and use the system. That is why GPS
units are referred to as receivers, they simply (or not so simply) receive
the radio signals continually being broadcast from the 24 satellites.
We say not so simply because the way GPS works is rather scientific
requiring the explanation of considerable technical information. This
includes the satellites broadcasting two sets of signals, one military
and one civilian.
The Department
of Defense’s ground control system operates the 24 orbiting satellites,
placing 12 in each hemisphere. GPS 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.
The GPS
should not ever be shut off to civilians. Despite the satellites broadcasting
separate military and civilian signals, even in time of crisis or war,
it is unlikely that civilians will ever be denied access to the system.
This is because of the great numbers of users that rely on the system
including the airlines, shipping, trucking, law enforcement and various
emergency response agencies. Even a Presidential Decision Directive
was signed that guarantees GPS will always be available to civilians.
Hand held
receivers are about the size of a TV remote control. They include a
built in antenna and view screen. A vehicle mount unit looks similar
to a marine fish finder with a larger screen and a remote antenna that
looks like a hockey puck. Portable units typically have a 2” screen,
and vehicle fixed mount units have a 4” screen. For visual ease
of operation, the largest unit practical should be used.
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Accuracy
remains about the same regardless of the size or price, as long as the
antenna has a clear view of the sky. A GPS receiver should be able
to lock onto its location anywhere in the world within 0 to15 meters.
With the government’s Selective Availability now shut off,
the accuracy of most units averages approximately within two to three
meters. Not perfect, but somewhere within 42 feet should be close enough
to find your truck at the trailhead. Thankfully in May
of 2000, the government eliminated Selective Availability. This
was a U.S. military safeguard that deliberately made the civilian signal
inaccurate up to 100 meters. It was designed to prevent unfriendlies
from using our own technology against us in targeting bombs and missiles.
Up to a 100 meter inaccuracy was not that big of a deal unless you happen
to be one of the unfortunates who died trying to find their shelter
during a blizzard. The government got around the security problem by
shutting down the signal around sensitive sites. That is why your screen
will go blank while driving by a military base or while spying on Area
51.
For
those users that require absolute accuracy such as land surveyors or
ship captains negotiating reefs, there is a system know as Differential
Correction or DGPS. Land based radio signals are used in conjunction
with satellite signals to greatly improve the accuracy. To take advantage
of this option, simply purchase a receiver capable of accepting DGPS
signals.
Most modern
receivers contain built in electronic map. For example, the Garmin
GPS 3 Plus includes North America, every major roadway and waterway
in Canada, the United States and Mexico. Receivers have only so much
memory preventing the maps from being very detailed, although they do
include an impressive amount of data. Do not expect the base map to
include the nameless dirt road traveled down to your favorite camping
spot. Fortunately manufactures provide additional memory allowing the
user to up-load greater detailed mapping information. Detailed topographical
maps are also available on CD ROM that include any part of the world.
Greater detail such as elevation lines suck up the available memory,
making it necessary to be selective on how much additional mapping can
be added. Some units also accept memory cards providing great detail
of larger cities or ocean ports.
A electronic
map is viewed in greater or less detail by using a Zoom feature.
When initially viewing the Map Page, the current location arrow
icon will be in the center of the screen. The screen will also have
a distance indicator to determine the scale of the current map. The
initial map will be larger making it easier to find a desired area.
Once the area is located, zooming in will increase the map’s detail.
Roads, waterways and their names will appear as the map is zoomed into
a specific area. Most receivers have a wide zoom range from 2000 miles
to 500 feet.
Using
a rocker keypad, a cursor in the shape of a small arrow will move about
the map. A dialog box will display changing latitude/longitude coordinates
and the distance from the current location. This is useful for finding
approximate distances to nearby locations. For example, from our location
in Springfield, Oregon, scrolling the cursor north up I-5, the arrow
is placed on downtown Portland, Oregon. It gives a distance of 103.5
miles. Distance is “as the crow flies”, which appears accurate
in this example because the driving distance is approximately 110 miles.
It also shows that its direction is 7°
north, and provides Portland’s latitude/longitude coordinates.
We now have the option to save this destination as a Waypoint.
Note:
GPS displayed distances are straight-line as the crow flies. Unless
flying or sailing, mileage has to be increased to estimate actual distance
traveled on the ground.
One
of the primary functions of using GPS is traveling to waypoints.
A waypoint (WP), is a selected point of interest location that is stored
in the receiver’s memory. The receiver provides useful information
on the traveling status to and from waypoints. This includes the distance
traveled, distance needed to go, and the estimated time of arrival based
upon the current speed. Navigation is simplified further with a provided
compass bearing and pointer arrow showing the direction needed to travel
to reach the selected waypoint.
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