For less than $200, you can buy a GPS receiver that displays your precise location, speed, direction, altitude, and can plan detailed routes thousands of miles long in seconds.However, the route is only as accurate as the map loaded in a GPS receiver. I’ve succumbed to GPS routing disappointments many times over the years—roads that dead end several miles in and pavement that later turns to dirt or gravel. I have been routed on sandy double tracks, where I’ve dropped the bike, and found slippery water crossings well beyond my riding capabilities. Fortunately, there are now some very good tech-tools that allow motorcyclists to just plan an interesting ride and avoid these mishaps.
How GPS works
The GPS system consists of 24 satellites that orbit the earth twice a day, with at least four visible at any given time. Each satellite broadcasts a radio signal containing position, orbital details, and a pattern of numbers that are also generated exactly in the GPS receiver. The satellite signal takes time to arrive, and the GPS receiver time-shifts its own pattern until they align. (Think of a movie where the lip sync is off.) Since radio propagates at the known speed of light, the distance to the satellite can be computed using this time-shift. Assuming you’re on the earth’s surface, the GPS receiver then knows it’s somewhere on a circle of points equidistant from the satellite. A second satellite narrows the uncertainty to two points, and a third selects the final point. But, the GPS receiver and satellite clocks must be synchronized within a billionth of a second for a precise location. Satellites have accurate atomic clocks, but the GPS clock is no better than a common digital watch. Fortunately, a 4th satellite signal allows the GPS to correct its clock and results in a position fix typically within 20 feet of the actual physical coordinates.
GPS Maps: Keeping them updated
Now, the GPS receiver internal map comes into play. These digital maps are created periodically by commercial companies and sold to GPS makers. They’re not perfect. The manufacturers allow users to report mapping errors via their websites, but repairs can take several map cycles to appear. Thus, keeping your subscription up-to-date is important if you frequently venture down obscure roads or want to use newly constructed highways.
You may also consider installing additional maps on your GPS. Most receivers come preloaded with a full North American road map. This large data-set must be compressed to fit, and, thus, details are sacrificed. Garmin, for one, sells higher resolution topographical maps by region that includes trails, lakes, surface elevations, and, most importantly, the roads are depicted in much greater detail. Having a terrain view should give you pause if the tiny road you’re considering crosses a stream or a mountain peak. Usually, you won’t find that information on the preloaded map.
Many GPS manufacturers also provide PC-based software to pre-plan a route that is downloadable to the GPS receiver. I frequently use PC map software to find likely roadblocks, pick twisty roads, and avoid urban areas en route. If your PC is connected to the internet, you can also use online maps, and, sometimes, the routes are also transferable.
Pre-planning your route
The best online pre-planning tool I’ve found is Google Earth, a free download here. Google Earth connects you with an online cache of satellite images covering the entire planet. The user interface is simple; you spin the earth with mouse buttons and zoom in with the scroll wheel (or screen sliders, if you have no wheel). The full-zoom detail near cities is good enough to pick out objects the size of mailboxes. Many urban locations have been photographed by Google’s camera cars, and, when available, you can switch to a 360 degree “Street View” good enough to read the street numbers on buildings.
Coupling Google Earth with the PC or GPS-created route is a fantastic way to visually fly along your route before leaving your driveway. Essentially, you do this by saving the waypoints (latitude/longitude pairs) that define your route to a disk file. Then you open the file from within Google Earth, and the waypoints show up as colored pushpins at the exact locations where you make your turns. Garmin’s MapSource software is supplied free with their receivers and makes it super easy to export a route to Google Earth. Inside the latest version of MapSource, create a route, left-click the “View” menu item at the page top, and select “View in Google Earth.” The Google Earth program launches automatically and zooms right in to your route. Waypoint pushpins are shown, and, as a bonus, a purple routing line is drawn on top of the actual roads that make up your travel plan. If you don’t have MapSource, there are many free (and commercial) tools available online to extract the route waypoints from your GPS and save them to a file. The details vary by GPS manufacturer, but you eventually need to get the file into the KMZ or KML format that’s readable by Google Earth.
A great program I use often to change waypoint file formats is called GPSBabel, and you can download it from www.gpsbabel.org. The program is free to download and is better than some commercial offerings. But, the authors would appreciate a small donation if you continue to use it.
If this seems too complicated, either find a geek to show you how, or chuck your GPS and stick with paper maps. Just don’t use an old map from your dad’s ‘57 Chevy glove compartment!
