Picture Viewer geocaching

Uncle Kridley krid at otisbean.com
Wed Feb 27 20:38:37 CET 2008

David Samblas Martinez wrote:
> Ok I will auto-answer to this question based on you
> answer with more accuracy data
> based on 
> http://www.eoss.org/pubs/nmeafaq.htm
> NMEA 0183 sentences= up to 82 Ascii chars-->one
> sentence per second-->82 bytes per second
> so 60*60*24*82=7084800

It's (probably) better than that, as long as you're not in constant
motion.  If you sit in one place for an hour, you don't need to store
3600 NMEA sentences that say the same thing.  It shouldn't be too hard
to write an algorithm that can tell the difference between "moving" and
"stationary", and store data accordingly.  Depending on the degree of
precision you desire, you can potentially reduce the storage
requirements drastically.

And if you're moving in an approximately constant speed and direction,
you can throw away all the data points along any straight line segment,
and only keep the beginning and the end.  I believe that this is what
Garmin devices do (based on the docs for my Garmin cycle computer).

However, this all may be moot, because GPS sucks up no small amount of
power.  I don't know that the Freerunner will have the juice to run GPS
all day long.  My Garmin gets 10-11 hours out of an 800 mAh battery (it
does some other bike-computer stuff, but that draws *very* little power,
given that non-GPS cycle computers can run for months on a couple button
batteries).  The Freerunner has a 1200 mAh battery, and its also running
a GSM modem, and doing other PDA-like stuff.  Heck, if you're trying to
store GPS data, you're going to have to have the processor awake the
whole time, which is another drain.

Hmm, then again, looking here:


It says:

"This would imply that with the CPU constantly on in low power mode, GPS
and GSM blipping on and off, and display off, the worst case power
consumption is probably around 70mW, leading to a battery life of 2 days."

So I guess we'll see when the hardware gets here...

      Dirk Bergstrom           krid at otisbean.com

More information about the community mailing list