Data collection when you travel long journeys
This page is about how to record a long journey for OpenStreetMap, in situations where you may not have access to computers for several days at a time.
The GPS then needs to record your entire journey in its internal memory, rather than downloading it to a computer daily like we do for shorter trips.
- Batteries - when out in the field for an extended period of time, running out of power is the major show stopper.
- Check the battery life of a GPS device when purchasing; most last about 8 hours, not long enough for a long day. Some last for 10 hours which is much better, particularly if you switch it off when taking a rest break.
- Consider buying a GPS device that takes standard rechargeable batteries so that you can afford to buy plenty of spares. Many devices require you to buy manufacturer-specific spare battery in the region of US$50 more.
- Tracklog memory - With one point per second, a GPX trace will take between 0.5 and 1 MB per hour. If your device uses memory cards, memory is usually not a problem. PDAs and smart phones with built-in or external GPS usually have the memory cards. Some handheld GPS devices also come with flash card memory, but they tend to be the "logging only" units. Most other handheld units store only 10000 points (Holux M-241 can store 120000 points), which you can stretch out to cover a few days' journey if you accept lower resolution. Notable exceptions here are the 'x' units from Garmin, eg, the Etrex Legend Cx, which is a handheld unit with integrated mapping screen, and replaceable flash card memory.
- Usefulness for walking - the "logging only" GPS units may be good for recording your journey, but they're not as fun to use and you can't see where you are, navigate to pubs with them, or use them to navigate off the hill in an emergency.
- Size - Geko 201 or Holux M-241 is much much smaller than "standard" handheld GPS's.
Many GPS units have an adjustable formula for saying when they log each point. Options tend to include
- Auto (about every 100 metres, or closer when turning a corner)
- By distance
- By time
Distance intervals are quite "reliable", as they give the same density of tracks no matter how fast you're going. (be careful in cities where streets might be closer together than that distance interval)
|Interval||Distance that can be logged|
Journey length that can be covered using a 10000-point tracklog, by setting the logging interval to various distances
Time intervals are good for seeing how fast you were going (footpaths appear as dense lines, motorways appear as sparse lines), and it makes it easy to see traffic lights, cafes, and other places where you've stopped. Remember to turn the GPS off when you have lunch, otherwise it'll record hundreds of points there!
|Interval||Logging time||6-hour days||distance walked||distance cycled|
Journey length that can be covered using a 10000-point tracklog, by setting the logging interval to various time periods.
Third column shows how many days you can log at that interval. Last two columns show the approximate distance walking or cycling that those times represent (assuming average 4mph, 12mph respectively)
- If you are doing your trip by car, buy a cigarette-lighter charger.
- If you regularly stop at a place where there's electricity, consider taking a (preferably small) charger for your device so you can recharge while having lunch. USB chargers come in sizes not much bigger than a 220V plug nowadays.
- If your device requires non-standard batteries, consider getting an external battery pack. There are external batteries on the market which can be charged via USB and can recharge any device with a USB charging connector, plus most other devices which charge at 5V. This allows you to recharge in the field when your battery runs out. Cost is in the € 20–30 range for some 1000 mAh (comparable to a smart phone battery – but beware, there will be some loss, and the battery pack will charge your device only to about 50%).
- There are also some solar and dynamo chargers out there, has anyone ever tried them? Dynamo chargers I'd expect to be of limited use, since charging a 1000 mAh battery at 500 mA (standard for USB) would require two hours of turning the crank to fully charge a flat battery.
- When tracking with a smartphone:
- Turn off all unnecessary communication (WiFi and Bluetooth won't be of much use anyway).
- If you have a second phone to use for phone calls, turn off GSM as well to increase battery life.
- Avoid waking up the screen - the backlight needs a lot of energy. However, you might not want your phone to go to sleep while tracking as this may affect the reception of your GPS, causing you to lose waypoints which you could have gotten otherwise.
- On most Android phones, putting the phone into airplane mode will disable all wireless communication, including GSM, but GPS will still work (though some models may take longer to acquire a fix when in airplane mode). The screen will go darker after some time with no user input, but tracking software should prevent your phone from going to sleep.
- Carry a separate camera for taking pictures rather than using your phone for it - this will save you both battery power and card memory.