[Talk-ca] GPS inaccuracy

[Harald Kliems]

Other things you could do: check if the Canvec data has been moved
after being imported. As I've said, Bing imagery can be improperly
aligned, but not everybody is aware of that. So it's possible that a
well-meaning mapper has moved the Canvec data to match the imagery.
Did you check your GPS devices accuracy reading? While they shouldn't
be taken too literally, they do give some indication of what's going
on (IIRC Garmin devices unfortunately do not write the accuracy
reading into the GPX file). You could also try to improve result by
making sure the GPS is in an ideal position: This usually means:
device parallel to the ground, with as little obstruction of the
upward line of sight. Putting it on top of a backpack or your
handlebar bag if you're riding a bike works best.

 Harald (who tends to get pretty good data with his Etrex Vista Hcx
but not so much with his smartphone)

On Mon, Nov 19, 2012 at 10:29 AM, Tom Taylor <tom.taylor.stds at gmail.com> wrote:
> I will do a resurvey in the way you suggest. It was really disappointing to
> find I couldn't trust my GPS at all (well, I did some mental adjustment of
> waypoints to place building entrances), and being off by a constant amount
> for 4 km certainly makes one suspicious.
>
> A bit to the north, my GPS survey of some footpaths behind a school matched
> Bing nicely. It would be really interesting to find some sort of disconnect
> in between.
>
> Je manquais de la courtoisie envers les francophones qui suivent cette
> liste. En sommaire, j'ai tracé une piste de longueur totale environ 4 km,
> mais l'a trouvé toujours environ 10 metres à l'ouest des entités déja
> presents sur la carte et les images Bing. Je vais faire un autre sondage
> pour mieux comprendre la situation.
>
> Tom Taylor
>
> On 19/11/2012 8:37 AM, Connors, Bernie (SNB) wrote:
>>
>> Tom,
>>
>> The transmission lines would not affect your GPS accuracy.  I agree
>> with Pierre that you could repeat the track and see if the two tracks
>> are similar.  Another thing you could do is identify several
>> identifiable points in the Bing Imagery such as the intersection of
>> two sidewalks, the corner of a sports field, etc.  Go to those points
>> and use your GPS to record a waypoint and use position averaging with
>> about 3 minutes of recording to get a more accurate location and then
>> compare those waypoints to the Bing imagery.  Position the Bing
>> imagery so they match up with your waypoints and then look at your
>> GPS tracks top see how they line up with the Bing Imagery.
>>
>> Bernie. -- Bernie Connors, P.Eng Land Information Infrastructure
>> Unit, SNB bernie.connors at snb.ca
>>
> ...
>
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