GPS Receivers
This is an informal and unofficial guide to GPS receivers specifically tailored to users who want a record of their position data. Many of the GPS receivers discussed here offer turn-by-turn navigation as well, but all keep a track log, a necessity for geotagging.
There are three major components by which we can evaluate all GPS receivers and their usability for keeping a track log.
- Reception quality -- In order to accurately determine your position, the GPS receiver must receive a radio signal from multiple satellites orbiting at about 20,000 kilometers above the earth. Understandably, the signal quality can be easily degraded in buildings, under tree cover, or in deep valleys and canyons. A degraded signal results in greater errors in your position and can often lose your position completely. You therefore want to find a more sensitive GPS receiver to decode a weaker signal and a higher quality antenna.
- Memory -- A gigabyte of memory could easily record a track point once per second for more than a year and costs next to nothing. However, GPS receiver manufacturers have yet to consistently provide a mechanism for logging track data to all this memory, so as a buyer you still need to investigate the track recording capabilities before purchasing.
- Connectivity -- Downloading the track data from the GPS to your computer is typically accomplished with USB or Bluetooth, although some GPS receivers still use RS-232 serial connections.
Of course there are a number of other factors to consider depending on your intended usage including battery life, portability, display, maps, navigational features, waterproofness and even support for external sensors like heart rate monitors for exercising or a fuel gauge for your boat.
Garmin 60CS and GPSMAP 76CS
These two units are almost identical to each other, the primary difference being that the 76CS has a larger form factor designed to float and has more built-in memory to hold maps. Both units offer a color screen, display maps, a good quadrifilar antenna and use a barometric altimeter for consistent elevation data.
The quadrifilar antenna should provide better reception than the ForeTrex 101's patch antenna, but when compared side-by-side this hasn't been consistently true. The same description applies here as with the ForeTrex: the signal is always lost inside buildings and quickly becomes spotty under moderate tree cover. During hikes it is not uncommon to completely lose the signal for 10-15 minutes in valleys or even with just moderate tree cover. Newer GPS receivers consistently perform much better.
The built-in memory comfortably records 10-12 hour days of backpacking for 8 days. However, we did find that the recording interval increases enough during car trips that the memory filled up within a couple of days. For car trips a week long or more, we needed to bring a laptop along just to periodically download and reset the internal track memory.
Both of these units have now been replaced by the Garmin 60CSx and GPSMAP 76CSx, which offer better signal acquisition and essentially unlimited track recording memory. Definitely purchase one of the newer models when possible.
Jeffrey
Garmin ForeTrex 101
The Garmin ForeTrex 101 was my primary GPS from summer 2004 through summer 2008. It is a minimalist GPS providing no built-in maps and a relatively small form factor.
Although the GPS receiver is much older and the built-in antenna is rather weak, I find the signal quality to generally be similar other GPS receivers from the same era, like the Garmin 60CS. However, the signal is always lost inside buildings and quickly becomes spotty under moderate tree cover. During hikes or runs it is not uncommon to completely lose the signal for 10-15 minutes. Newer GPS receivers consistently perform much better.
The ForeTrex 101 has built-in memory that comfortably records 10-12 hour days of backpacking for 8 days without filling up. There are no options to set the recording interval, but I find the interval to be perfectly reasonable.
The largest drawback to this GPS unit is that it exclusively uses a serial connection, something missing from Macintosh computers for a decade now. You need to purchase an adapter from Garmin to first convert to a standard RS232 jack, and then a Serial-USB adapter from someone like Keyspan.
The small form factor, excellent battery life, and relatively low cost made this GPS a very good data logger for the time, however, with few exceptions I think most users would be better off with a more modern GPS. As of September 2008 Garmin still sells this GPS model new.
Jeffrey