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    Re: Digital Image CN Exercise #2
    From: Marcel Tschudin
    Date: 2010 Apr 8, 21:55 +0300

    Just a few notes regarding your last posting:
    The photo which I attached was a copy of the original. So nothing has
    been done to it. The sun on it has a yellow rim and the size of it
    matches close the expected size; this would indicate that the exposure
    is "reasonable". In my notes I mentioned that the horizon was hazy
    which results in a fuzzy line. There was also a cloud bank very close
    to the horizon.
    As you also mentioned, the main reason seems indeed to be the
    different measurement of the heights. To likely lesser extend it might
    also be the program which you use. I don't know the program from
    Henning Umland. Could it be that for this sort of calculation it
    should be used iteratively? I mean this in the sense that you get a
    first estimate from your start location and use then this estimated
    location as a new start location. One repeats this until the computed
    altitude agrees with the observed altitude.
    Regarding adding a filter. With my present equipment this is - at
    least in my view - practically not feasible. Remember that I hold in
    my hand also the chronometer.
    On Thu, Apr 8, 2010 at 7:31 PM, Greg Rudzinski  wrote:
    > Marcel,
    > I see now that the north point of Kinali Island was to be use for a bearing
    > to get the true photographer location. Heybeli seemed to be a better fit. To
    > do better with the pixels I would need the original photo unedited or
    > adjusted. Even so both the horizon and the Sun seemed over exposed which
    > would cause me to measure a smaller angle and increasing my intercept away
    > from the assumed position. I did an upper limb observation and got an
    > intercept of 3 NM away which is closer but still I would have selected
    > Heybeli for my bearing.
    > When taking these pictures try dimming the Sun with filters held over the
    > upper half of the field of view and then adjust exposure for a dim yet still
    > visible horizon. I find that this can be done most easily with a circular
    > polarizer attached to the lens and a second circular polarizer out of its
    > frame held over the upper half of the field of view then rotated with
    > fingers until a dim sharp image of the Sun is viewed with an unfiltered
    > sharp horizon in the lower half of the field.
    > GRudzinski
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