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GPX dt / ds settings

 
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HenryC



Joined: 29 Nov 2007
Posts: 2
Location: New Zealand

PostPosted: Thu Nov 29, 2007 10:11 am    Post subject: GPX dt / ds settings Reply with quote

The default setting is GPX dt 60 and GPX ds -1. The interpretation is clear, i.e. logging once every 60 seconds; and ignore distance rule.

But I am not clear when both settings are operational. How do the two GPX dt and ds settings interact with each other? Which one takes precedence?

For example, for the setting GPX dt 60 and GPX ds 10, does it mean tracking occurs:

1. as soon as after 1 minute has elapsed OR distance travelled for 10 metres, whichever occurs first ... or

2. only if it is BOTH after 1 minute AND distance travelled has exceeded 10 metres?
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kruch
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Joined: 02 Jul 2006
Posts: 5674

PostPosted: Thu Nov 29, 2007 11:23 am    Post subject: Reply with quote

Variant 1 is true - OR

Besides that, TB may decide to log another location(s). The basic algorithm detects trajectory curves, so may actually get a few more locations recorded in addition to those that matched "dt ds" criteria.
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HenryC



Joined: 29 Nov 2007
Posts: 2
Location: New Zealand

PostPosted: Fri Nov 30, 2007 12:21 am    Post subject: Reply with quote

Great. Thanks for the fast response.

This is good in that if I set this to dt=3600 and ds=10, the logging will be detailed enough to track the fine curves when travelling, but still would pause automatically if I stay put for an hour.

But, is there a mininum interval (say no more frequently than one point per second) that logging will occur? For example, if I am travelling at 100 km/hour, then ds=10 would imply logging at nearly 3 points per second! The resultant GPX file would get too big in this case.
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kruch
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Joined: 02 Jul 2006
Posts: 5674

PostPosted: Fri Nov 30, 2007 6:56 pm    Post subject: Reply with quote

This is why by ds=-1 by default - only curves are recorded. But with ds=1000 you should also get curves nicely recorded, but when travelling on a straight highway at 100 km/h you should get a record only every kilometer passed.

In other words - a position is recorded when either a) ds criteria is met or 2) curve is detected or 3) dt passed. That's how it is intented to work; if it does not, then there is a bug Wink

ds is important for walking speed, when course reported by GPS is a bit unusable, so, for speed < 3 km/h (approx IIRC), curve detection algorithm is not used. There is an improvement planned to calculate speed and course for low speed and not to rely on values reported by GPS.
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