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    Re: Digital Image CN Exercise #2
    From: Marcel Tschudin
    Date: 2010 Apr 8, 16:47 +0300

    Your location is further off from the true location than what I would
    have expected from this photo. Comparing the results for the true
    location with what you measured in the photo corresponds to an error
    in sun height of 10 pixels. I think the photo is somewhat better than
    that. You also selected the LL which is more critical relative to
    refraction. My measurements of the photo result in 6 pixels difference
    for the LL and in 3 pixels for the UL. It could however well be that
    you didn't put the same effort in measuring the photo than what I do
    when I enter those in my database. For this the pixels of each of the
    four limbs (left, right, upper and lower) are measured four times,
    using then the resulting mean values. The difference between measured
    and expected diameter indicates whether the positions of lower and
    upper limb have to be corrected for over exposure or under exposure.
    The apparent horizon is measured four times together with the upper
    limb and four times with the lower one. This picture actually also
    shows that quite often the apparent horizon is more difficult to
    measure than the sun. The sheet "Measurements" in the attached Excel
    file shows the values which I extracted from the photo. The sheet
    "Locations" in this file shows how the (estimated) locations were
    found by trial and error. For this I assume a location and calculate
    the apparent height of the sun, this until I find one having a
    reasonably small difference. I also attach a screen shot from Google
    Earth showing our results and the location from where the photo has
    been taken.

    File: 112797._p1030774-16-13-30-analyses.xls

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