[Talk-ca] GPS inaccuracy

[Brent Fraser]

Tom,
Your results are not unusual.  A newer handheld navigation-grade 
receiver has an accuracy of 3 to 5 meters at best (older ones without 
WAAS have an accuracy of 10 m).  Slowly changing (over hours) 
atmospheric effects can introduce an systematic offset into your 
coordinates of 3 to 5 or even 10 meters.

And as others have pointed out, the positional [in]accuracy of Bing and 
Canvec could exceed 10 meters.

Best Regards,
Brent Fraser

On 11/19/2012 8:29 AM, Tom Taylor 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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