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;-) There's also Inside GNSS, whose editor is the former editor of GPS
World:
http://www.insidegnss.com/

On 5-Jan-13, at 12:14 PM, Thomas Sult wrote:

> The thing of general use to me is ... WOW there is a GPS world
> magazine!
>
> Tom Sult
> Sent from my iPhone
>
> On Jan 5, 2013, at 8:10, "Richard B. Langley"  wrote:
>
>> Warning: Slightly off topic; delete if not interested.
>>
>> Not wanting to muddy the waters, but for those interested, here is
>> a link to an article on GPS precision and accuracy that appeared in
>> my GPS World column a few years ago:
>> http://gge.unb.ca/test/gpsworld.may10.pdf
>>
>> There may be something of general use that could also be considered
>> when looking at the statistics of CN observations.
>>
>> -- Richard Langley
>>
>> On 5-Jan-13, at 6:24 AM, Marcel Tschudin wrote:
>>
>>> ... when should I be using stdDevPop and when should I be using
>>> stdDevSamp?
>>>
>>> I try to explain the difference in a general understandable way.
>>>
>>> The calculation of the standard deviation requires to know the
>>> mean value. The difference between the two functions results from
>>> whether the mean value from the given data set represents the
>>> exact mean or is an estimated mean.
>>>
>>> If the given data represent all of them, i.e. they represent the
>>> complete population, then their mean value is exact and the
>>> standard deviation is calculated on the basis of an exact mean
>>> value. However, to have a complete population and know the exact
>>> mean is rather the exception. It is more likely that we have some
>>> selected (measured) values out of a greater population which is
>>> assumed infinite and where the exact mean value is unknown; the
>>> mean value of the given data set represents therefore an estimate,
>>> and the standard deviation is calculated on the basis that the
>>> mean value of the data set is an estimate.
>>>
>>> The difference between stdDevPop and stdDevSamp is therefore:
>>> stdDevPop() calculates the standard deviation understanding that
>>> the entered data are all of the population and that the mean value
>>> of the entered data is the exact mean value.
>>> stdDevSamp() calculates the standard deviation understanding that
>>> the entered data represent a sample from an infinite population
>>> and that the mean value of the entered data represents therefore
>>> an estimation for an infinite population.
>>>
>>> Now, what does the standard deviation mean? This is a measure for
>>> a probability that an other data (an other measurement taken under
>>> the same condition) will be within (or outside) certain limits. If
>>> we look at Greg's last data and designate with  the mean value
>>>  = 0.575' and with Sx = 0.159' the standard deviation of his
>>> sample with 20 measurements, then
>>>
>>>  +/- 1Sx (+/- one standard deviation)
>>> means that 68% or about 2 out of 3 other measurements of the same
>>> type are expected to be within (or about 1 out of 3 outside) the
>>> range between 0.416' and 0.734'.
>>>
>>> Generally the results provide the mean and one standard deviation
>>> as above. However, these values allow representing the result also
>>> related to other probabilities, like e.g.
>>>
>>>  +/- 2Sx (+/- two standard deviation)
>>> means that 95% other measurements of the same type are expected to
>>> be within (or about 1 out of 20 outside) the range between 0.257'
>>> and 0.893'.
>>>
>>>  +/- 3Sx (+/- three standard deviation)
>>> means that 99.7% other measurements of the same type are expected
>>> to be within (or 3 out of 1000 outside) the range between 0.098'
>>> and 1.052'.
>>>
>>> I hope it helps.
>>>
>>> To those of you who are familiar with the subject: Please feel
>>> free to improve or even correct these general explanations where
>>> necessary. Thank you.
>>>
>>> Marcel
>>
>> -----------------------------------------------------------------------------
>> | Richard B. Langley                            E-mail:
>> lang@unb.ca         |
>> | Geodetic Research Laboratory                  Web: http://www.unb.ca/GGE/
>>  |
>> | Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506
>> 453-5142   |
>> | University of New Brunswick                   Fax:      +1 506
>> 453-4943   |
>> | Fredericton, N.B., Canada  E3B
>> 5A3                                        |
>> |        Fredericton?  Where's that?  See: http://
>> www.fredericton.ca/       |
>> -----------------------------------------------------------------------------
>>
>>
>>
>>
>
>
>

-----------------------------------------------------------------------------
| Richard B. Langley                            E-mail:
lang@unb.ca         |
| Geodetic Research Laboratory                  Web: http://www.unb.ca/GGE/
  |
| Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506
453-5142   |
| University of New Brunswick                   Fax:      +1 506
453-4943   |
| Fredericton, N.B., Canada  E3B
5A3                                        |
|        Fredericton?  Where's that?  See: http://
www.fredericton.ca/       |
-----------------------------------------------------------------------------

   

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