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    Re: Estimating height of eye
    From: Richard B. Langley
    Date: 2013 Apr 10, 13:26 -0300

    It would be averaging the effects of measurement (pseudorange) imprecision 
    (random over longish time intervals) and multipath (not random and not 
    repeatable except for a fixed location with the same satellites one sidereal 
    day to the next). And, to a lesser extent, tropospheric delay errors and 
    other minor model deficiencies. Two sites, some distant apart, would 
    experience different errors although the pseudorange-based DGPS technique 
    (such as that supported by the Coast Guard) uses the errors computed at a 
    reference station to improve the positions of a rover (in real time).
    -- Richard Langley
    
    On 2013-04-10, at 1:20 PM, Marcel Tschudin wrote:
    
    > 
    > Thank you, Brad, for finding this Android app for me. I presume that
    > the 1 m represent an absolute accuracy and that measurements of height
    > differences may possibly attain a higher accuracy. I will give this
    > affordable gadget a try and perform some tests with it.
    > 
    > Marcel
    > 
    > 
    > On Wed, Apr 10, 2013 at 6:28 PM, Brad Morris 
    >  wrote:
    > > ________________________________
    > >
    > > Hi Marcel
    > >
    > > There is an app in the Android market called "Precision GPS Pro".  The cost
    > > is US$0.99
    > >
    > > It claims a 1 meter elevation accuracy after averaging, although they do not
    > > indicate how long an average you require to achieve that.
    > >
    > > The free version of this app does not do elevation averaging.
    > >
    > > I have not tried this app.
    > >
    > > Brad
    > >
    > > On Apr 9, 2013 6:21 AM, "Marcel Tschudin" 
    >  wrote:
    > >>
    > >> ________________________________
    > >>
    > >> In my sunset observations the guesstimates for the HoE of probably not
    > >> better than +/- 20% are indeed a weak point. But how weak? The dip is
    > >> proportional to the square root of the HoE which means that the
    > >> estimated dip error is only half of the estimated HoE error. For the
    > >> average HoE of 3.5m the "normal" dip is 3.3 moa and a 10% error of it
    > >> therefore +/- 0.33 moa. This corresponds in the photo to slightly more
    > >> than one pixel which is 18 seconds of arc.
    > >>
    > >> Frank, you mentioned estimating HoE within about +/-5%. I'm wondering
    > >> whether you would also be able to attain such an accuracy by climbing
    > >> over the rocks as shown in my photo:
    > >>
    > >> 
    https://mail-attachment.googleusercontent.com/attachment/u/0/?ui=2&ik=b33d2c81ba&view=att&th=13ddab531282f2e7&attid=0.1&disp=inline&realattid=f_hf5h7cfp0&safe=1&zw&saduie=AG9B_P-DvbGAuAxTxtruQd29-avq&sadet=1365502394438&sads=w4N-7jPt0vbdfN6eZHKSEaR8vQ0
    > >> For my average of 3.5 m this would correspond to less than 20 cm or
    > >> what might be more familiar to you to about half a foot.
    > >>
    > >> In order to verify my guesstimates I do indeed consider to perform
    > >> some additional measurements. I'm wondering how good I could measure
    > >> it using GPS and also the Russian version of it. I have no experience
    > >> in using these systems. I understand that I would have to measure both
    > >> levels, eye and sea level and then take the difference. Is there an
    > >> Android application which I could load on my Samsung pad allowing to
    > >> collect measurements over a longer time period which then calculates a
    > >> mean altitude and its standard deviation? What are the sort of result
    > >> one could obtain this way?
    > >>
    > >> Marcel
    > >>
    > >> View and reply to this message: http://fer3.com/arc/m2.aspx?i=123477
    > >
    > > View and reply to this message: http://fer3.com/arc/m2.aspx?i=123498
    > 
    > 
    > View and reply to this message: http://fer3.com/arc/m2.aspx?i=123499
    > 
    
    -----------------------------------------------------------------------------
    | Richard B. Langley                            E-mail: lang---.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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