a GPS suitable for hiking
you to choosing a suitable GPS for your hiking needs, it
is important to have a reasonable understanding of what
is on offer along with how they work.
are several components that need to be looked at. There
is the GPS receiver (or antenna) itself, which plays an
important part. Then there is the portion of the system
which uses the received information to estimate where the
device is located on an internal map.
there are the various capabilities for route planning and
recording, which vary from unit to unit. Finally, the display
portion of each solution type can vary considerably, from
limited location information to full color three dimensional
maps of the immediate surroundings and advised route.
actual principal of GPS is very easy to appreciate, since
it produces similar results to traditional "triangulation" although
GPS does not use angles. If one imagines an orienteer needing
to locate themselves on a map, they first need to be able
to find at least three points that they recognize in the
real world, which allows them to pinpoint their location
on the map.
can then measure, using a compass, the azimuth (This is
the direction of a celestial object, measured clockwise
around the observer's horizon from north) that would be
needed to take them from the point on the map to their
current position. A line is then drawn from each of the
three points, and where the three lines meet is where they
are on the map.
this into the GPS world, we can replace the known points
with satellites, and the azimuth with time taken for a
signal to travel from each of the known points to the GPS
receiver. This enables the system to work out roughly where
it is located, it is where the circles representing the
distance from the satellite, calculated on the basis of
the travel time of the signal, intersect.
course, this requires that the GPS locator has the same
coordinated time as the satellites, which have atomic clocks
on board. To do this, it cross checks the intersection
of the three circles with a fourth circle, which it acquires
from another satellite.
four circles no longer intersect at the same point, then
the GPS system knows that there is an error in it's clock,
and can adjust it by finding one common value (one second,
half a second and so on) that can be applied to the three
initial signals which would cause the circles to intersect
in the same place.
the scenes, there are also many complex calculations taking
place which enable the system to compensate for atmospheric
distortion of the signals, and so forth, but the principle
remains the same.
Updates & Mapping
choosing a GPS, it is important to bear in mind that each
type will be updated in a different way. For example, dedicated
in-vehicle units tend to be updated via a CD, which has
to be purchased from the road map data supplier.
which are attached to a PDA, as well as most handheld dedicated
GPS devices, are usually updated via a PC. They also need
maps, but said maps can usually be acquired at a much lower
price than the dedicated branded ones needed for other
able to update the device easily and at a reasonable cost
is a very important part of the decision process; unlike
other consumer devices that you purchase, the cost of ownership
of a GPS unit is proportional to its usefulness.
less you spend on maintaining it, the less useful it becomes
since the road networks are always changing. This is perhaps
less important for devices aimed at hiking and orienteering,
but could be a factor in deciding whether a multi-function
device is better than one dedicated to a specific use.
software vendors have solutions for preparing maps which
can be uploaded into the GPS unit. For example, many are
based around the mapsource system which permits users to
define their own maps, perhaps scanned from a real one,
in order to get the most out of their GPS.
Accuracy & Portability
is paramount, then it is also important to choose a unit
that is equipped with a WAAS (Wide Area Augmentation System)
capability assuming it is available in the region the unit
is being used.
is a satellite service which provides additional correction
information to the GPS receiver which enables it in order
to increase its accuracy.
equipped devices might be especially useful for road users
and those involved in either door-to-door selling, or providing
a service which requires them to be able to pinpoint their
position right down to a few feet.
other hand, it is useless to purchase a WAAS capable system
if the service is not available in the area in which the
device is to be used.
is a key part of the decision process, then it will usually
be a trade-off against accuracy, whether that accuracy
stems from poor GPS signal acquisition, or less powerful
software coupled with a less detailed map.
features to consider when selecting GPS for hiking:
features needed on a GPS can be a personal thing however
when hiking is involved the features needed are a generally
more extensive than for other uses such vehicle navigation
for example. Listed below are the important features recommend
for GPS when it comes to hiking. These do not include the
standard features present on All receivers.
is best to have a "Map" screen rather than a numerical
lon/lat position fix, this makes it much easier to see
where you are relative to reference waypoints.
in Maps" make it a lot easier when it comes to orientation
and estimating distance to nearest roads etc.
memory" We recommend at least 20 megs for a mapping GPS
although you can get by with as little as 1.4 megs if you
are only using local topo maps on your hikes.
capability" it is best to have at least 20 routes
get one that can store at least 500.
Datum capability" make sure all the datums you will want
to use are included in the GPS you select.
size and readability" Screen size and your ability to read
it are important especially when it comes to viewing fine
detail. B&W screens are fine for hiking. Many color screens
are hard to read in direct sunlight, however the more advanced "Trans
Reflective Color screens" are an exception as they are
easy to read in bright sunlight.
to next waypoint" features are essential when it comes
channel parallel receiver system" provide the best reception
in difficult terrain and tree cover.
Make sure the unit is compact and light to carry.
The unit should be rated "submersible" making it waterproof.
life batteries" avoid the need to carry so many batteries.
However it is always advisable to carry at least one replacement
amplified antenna" although not essential, they handy to
have if you are going to encounter heavy tree cover or
difficult terrain conditions involving multi paths etc
Ability to upload topo maps is also a useful feature to
consider although not essential.
the end, the choice is reasonably straightforward - if
price is a deciding factor, then buy the most expensive
one you can afford which fits your needs.
to think about the following:
is affected by weight and size, as well as the antenna.
This could have an effect on the features that the device
offers - clearly if the screen is tiny, and the whole unit
is about the size of a cell phone, then some advanced features
will not be fitted.
mapping and updating capabilities are also important. Should
it be able to accept any old map from a PC, or is it enough
that the unit is replaced after 5 years? Technology moves
almost as fast as the roads are updated, so this could
be an option.
are there any specific environmental options that are needed,
such as waterproofing, rugged shock-proof design, or other
features that make one device more attractive than another?
these questions will help determine what type of GPS receiver
that is right for you, and at the right price.