[OSM-talk] Defective GPS trace

[Aun Johnsen]

The accuracy shown on your GPS unit is not necessary the actual accuracy,
but just a calculated accuracy depending on the signals your unit is
receiving. You can experience athmospheric disturbance, plasma-effects,
signals reflected off tall buildings, canyon or urban canyon effects, bed
satellite constillations etc. If you have SBAS (WAAS/EGNOS) activated you
might see an improvement in the signal, but mind that if you are outside the
official coverage of such systems you might experience that these
corrections are in fact increasing the error. If you have access to other
forms of augmentation, such as IALA, make sure that you receive signals from
the closest station.

Even if you have access to good arial photography, remember that it might be
out of alignment, it can be a good advise to gather some good fixes to check
the alignment of your photos, this can be several GPS tracks along your
trail.

The problem of GPS devices drifting off is minimal, though more common in
small and cheap devices, in many cases simple augmentation can counter for
this, but the built in memory of your unit might also help in adjusting (for
better or worse).

On Fri, Jan 1, 2010 at 8:39 PM, Igor Brejc <igor.brejc at gmail.com> wrote:

> You can also use Oregon's Waypoint Averaging function to make more accurate
> positioning of waypoints. But you need to do this at different times (say on
> you next hiking trip when you cross the same waypoint) for this to be really
> effective. With couple of accurate waypoints it is easier to detect track
> inaccuracies.
>
> Igor
>
>
> On Fri, Jan 1, 2010 at 9:18 PM, Michael Hufer <michael.hufer at gmx.de>wrote:
>
>> On the Oregon 550(t) you will find the satellite almanac-screen if you
>> touch
>> the "five-bars" satellite reception indicator.
>>
>>        Micha H.
>>
>> > On Sat, 2 Jan 2010, Craig Wallace wrote:
>> > > You can check the satellite screen on the Garmin. It should show an
>> > > estimated position accuracy.
>> > > Also, you can look at which satellites its receiving. If its locked on
>> > > to a reasonable number of satellites in a decent spread across the
>> sky,
>> > > you can be fairly confident in its accuracy.
>> >
>> > The Oregon 550 lacks a pictorial representation of the almanac, and only
>> >  has five bars telling you whether it thinks it has good PDOP or not.
>> > Or it might, but as I've had mine 8 days , the same as Steve has, and it
>> is
>> >  in a menu I haven't found yet ;)
>> >
>> >
>>
>
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