Category Archives: navigational tools

Altimeter

Using an altimeter as a navigation tool

An altimeter is a tool that measures altitude above a reference point. It works by detecting small changes in atmospheric pressure, and bushwalkers can use a hand-held or wrist-mounted device.

Knowing altitude can help to verify the user’s location, particularly on long uphill sections. When used conjunction with a topographic map, a barometric altimeter is often more accurate than a GPS unit, which is susceptible to failure from satellites dropping in an out of availability and being wildly inaccurate when all available satellites are near the horizon.

Since barometric pressure is affected by weather and changes in weather, bushwalkers need to recalibrate the device periodically at a known location (e.g. trail junction, hill).

GPS/Smartphones/Tablets

Using a GPS, smartphone or tablet as a navigation tool

A GPS navigation device gives the user their location anywhere on earth. GPS stands for Global Positioning System, a space-based navigation system that uses satellites to identify a location. As long as the device has an unobstructed line of sight to four or more GPS satellites, it’s accuracy is within 20m, more than adequate for all on-track bushwalking needs.

GPS technology is now so cheap that most smartphones and tablets have a GPS chip that tells the user where they are. Providing suitable maps are loaded, a smartphone or tablet can be as useful as a conventional GPS unit. Both can identify your location with up to 20m accuracy. But if the right maps aren’t loaded, a GPS unit, smartphone or tablet can still inform the user of their location coordinates. The user then has to be able to translate coordinate positions between the device and a physical map using the correct datum and projection.

CAUTION: a GPS unit only gives location information. Users must still be able to plan and follow a route, which requires map reading skills.

Knowing location information is useful, but only one component of navigation. It’s no use knowing that your location if you can’t then use that information to get to your destination. Often, going directly from A to B in a straight line is not the best way, or worse, there’s a massive cliff in between. Route planning is about determining the best way to traverse the landscape, and navigation is about executing that plan.

Most GPS units are reasonably shock-proof and are waterproof at the very least for incidental exposure to water of up to 1 meter for up to 30 minutes. For smartphones, it’s possible to buy waterproof and shockproof cases, a good idea on any bushwalk. A waterproof case means you can also use the device in the rain.

However, just like any tool, GPS technology can fail! For example, the GPS unit might jam up, the batteries could run out, the unit could get dropped, or water gets inside the electronics. On a bigger scale, satellites can drop out or become wildly inaccurate if their position is near the horizon relative to you. A GPS will not work if it doesn’t have an unobstructed line of sight to four or more GPS satellites. For example, at the base of cliffs a GPS will give terrible results, and in dense forest the signal may be faint.

So that’s why it’s a good idea to carry backups. Often, a GPS user will also take a compass as a backup. Likewise, compass users will often bring a GPS unit as their backup.