[Talk-GB] Ficticious embankments? Vandalism.

[Warin]

On 17/3/20 8:53 pm, John Aldridge wrote:
> On 17-Mar-20 02:08, Warin wrote:
>> A single GPS trace is fine if that is all there is, better to average 
>> many GPS traces, in some locations I have 50+.
>
> Though, AIUI, once you've reached this level of precision, remaining 
> errors are likely to be systematic (e.g. satellites in a particular 
> direction being generally received via a -- delaying -- reflection 
> rather than directly). No amount of averaging will help with that.


Yes, a source of error. When placed over some reasonable imagery any 
discrepancies can be seen, evaluated and if necessary compensated for. 
However most users will not be aware of the discrepancy as they would be 
using another GPS to 'see' it.

If the GPS tracks are separated by days, weeks and months then the 
satellites will have changed, and the satellite positions too. Usually 
there will be 'outliers' that are more than 2 standard deviations from 
the average. It is valid to delete these from computations.

I don't bother with the calculations and do it by eye, more satisfying 
than loading it all into a program, taking the result and entering it. 
And I like to see the raw data anyway.