Submitting ultra trac mode gpx files for ECE/DIY.

[Greenbank]

Recording wise Ultratrac is basically letting you set the recording interval, unlike normal mode rather than have the GPS receiver on constantly the device has to re-enable the GPS before each recording so if you've got it set to record every minute then it'll spend 5 to 10 seconds per minute (in order to reobtain GPS lock etc) with the GPS receiver enabled rather than the full 60.

Well if you say so - but to be honest I find that hard to believe.  It looks counter-productive to me, in terms of battery-saving.

Computing the position from the 4+n satellite signals is computationally expensive (and therefore a reasonable power drain). It's not any cheaper/easier because you did it a second ago, it's roughly the same amount of work each time, and the unit doesn't work any 'harder' whilst attempting to get a lock (if anything it's less computationally expensive the fewer satellite signals it has received emphemeris data for).

[FifeingEejit]

The downside is the accuracy as it records as soon as it has the lock; and as most will likely have seen the accuracy just after getting the lock can be diabolical.
MY colleagues are just about used to seeing me standing at the front door at lunch times waiting for the Fenix2 to stop claiming I'm traveling at 100mph

[Kim]

Recording wise Ultratrac is basically letting you set the recording interval, unlike normal mode rather than have the GPS receiver on constantly the device has to re-enable the GPS before each recording so if you've got it set to record every minute then it'll spend 5 to 10 seconds per minute (in order to reobtain GPS lock etc) with the GPS receiver enabled rather than the full 60.

Well if you say so - but to be honest I find that hard to believe.  It looks counter-productive to me, in terms of battery-saving.

Computing the position from the 4+n satellite signals is computationally expensive (and therefore a reasonable power drain). It's not any cheaper/easier because you did it a second ago, it's roughly the same amount of work each time, and the unit doesn't work any 'harder' whilst attempting to get a lock (if anything it's less computationally expensive the fewer satellite signals it has received emphemeris data for).

I did some real-world power measurements of an eTrex and concluded that turning the GPS off made a negligible difference to power consumption.  It's the computation involved in doing things like rendering the map that raised the power consumption above the base level.  And the backlight, obviously.

Presumably the real win here isn't from powering down the GPS, but from not processing the data.

[FifeingEejit]

Garmin suggest reducing the map speed on the Etrex...
I presume that means reducing how often the screen is refreshed.

mapping and navigation is known to be a big battery eater

the quoted difference between Ultratrack on the Fenix2
16 hours in Normal GPS mode
50 hours in UltraTrac GPS mode with one-minute polling interval
Up to 5 weeks in Watch mode

have never reached those figures but the UltraTrac does give a lot more life.

[Greenbank]

Recording wise Ultratrac is basically letting you set the recording interval, unlike normal mode rather than have the GPS receiver on constantly the device has to re-enable the GPS before each recording so if you've got it set to record every minute then it'll spend 5 to 10 seconds per minute (in order to reobtain GPS lock etc) with the GPS receiver enabled rather than the full 60.

Well if you say so - but to be honest I find that hard to believe.  It looks counter-productive to me, in terms of battery-saving.

Computing the position from the 4+n satellite signals is computationally expensive (and therefore a reasonable power drain). It's not any cheaper/easier because you did it a second ago, it's roughly the same amount of work each time, and the unit doesn't work any 'harder' whilst attempting to get a lock (if anything it's less computationally expensive the fewer satellite signals it has received emphemeris data for).

I did some real-world power measurements of an eTrex and concluded that turning the GPS off made a negligible difference to power consumption.  It's the computation involved in doing things like rendering the map that raised the power consumption above the base level.  And the backlight, obviously.

Presumably the real win here isn't from powering down the GPS, but from not processing the data.

Well the Forerunner 935 has no real mapping capability (it's just a watch) and the specs show the difference that UltraTrac gives:-

Battery life, watch mode: Up to 2 wk. with activity tracking, smartphone notifications, and wrist-based heart rate

Battery life, activity mode: Up to 24 hr. in GPS mode and wrist-based heart rate

Battery life, UltraTrac mode: Up to 60 hr.
                                             Up to 50 hr. with wrist-based heart rate

So it doubles from 24h to 50h going from GPS mode to UltraTrac mode and everything else staying the same.

[Kim]

Somehow I'd forgotten that it was a watch.  Makes sense that the GPS chipset starts to dominate the power budget...