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Posts posted by kr.afol

  1. Automatic mode records points based on when needed.

    You can imagine the function, in two dimensions, like this:


    Start out from some point, to get an initial condition. Store that point.

    Move some arbitrary distance. Store that point too.

    Now draw a line between these two points, passing point two, thus projecting into your (possible) future.

    As long as you keep moving along that line, do nothing.

    When you stray off the line by some amount of distance (this is where the sensitivity setting of Auto recording comes in), store a new point where you are now.

    Draw a new line from your second last point through your last point, and repeat the process of checking how near that line you are, to determine if a new point should be stored.


    This description is only for two-dimensional positions. Now add a similar algorithm for speed and elevation changes, and you have the whole scenario in front of you.


    The advantage of automatic mode is that it doesn't waste memory, as it will not spend points every set distance/time, if there is nothing to tell (steady state), but stores several points when you do intricate manouvers.


    OK. so I was on the right track (so to speak) in thinking it was change of direction that would trigger a recording, as it seemed to me that recording changes would be the most efficient in terms of points. However, as the reporting has a 2D bearing which often appeared to be the same for successive (and often short) legs, I was thinking my theory didn't fit the data I was seeing. However, it may have been that there was a sufficient change altitude or speed that was causing the recording of the point. That makes sense.


    It's perhaps worth explaining why I am so interested in how the tracking is being done. We went on a month's holiday recently driving from Brisbane to Perth and back (about 12000 km) and we were using the Garmin to record waypoints and tracks in the hope we could automatically (or at least semi-automatically) geo-locate our photos. Now in the 2 years we've owned the Garmin, we've never had a problem with recording track data. All the track data we've ever recorded was still fitting in the memory, but with the benefit of hindsight, it was a large number of fairly short trips. So we set off to Perth with the tracking on, assuming we'd have a month of track data on our return. Sadly we found we had about 4 days of track data because the Garmin didn't have sufficient memory and was overwriting. So, I'm now very motivated to try to work out the best settings for trackings to make the most efficient use of the memory to avoid this problem in future (I'd rather not have to cart a laptop around just to upload track info). But of course the solution might lie in getting a camera with a builtin GPS (still a bit of an expensive option but probably the preferred option in terms of what we are actually trying to achieve) or getting another GPS with more track memory.


    Thanks for everyone's thoughts.



  2. I have a Garmin eTrex Vista C. When it is tracking, you can have it in one of three modes: Distance, Time, and Auto.


    Now, it's pretty clear what is going on in Distance and Time mode, it records your location at fixed distance or time intervals.


    But what is it doing in Auto mode? The manual rather unhelpfully says that it is by "frequency". But frequency of what? I've taken a look at the tracks produced and I can't see any obvious pattern (my initial theory was change of bearing but that doesn't seem to stack up against the data).


    So I was wondering if anyone knows?

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