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    Re: Digital Camera Celestial Navigation
    From: Greg Rudzinski
    Date: 2008 Jul 8, 16:14 -0700

    Digital Camera Cel Nav Follow-up
         Photos of the sun taken at high altitude through a filter can be
    augmented to full screen on a laptop for determining minutes of arc
    (M.O.A.) per pixel.
    Example for 4 power zoom on a Canon PowerShot A560 :
    Solar diameter 07/07/2008    31.46' = .291 M.O.A. per pixel
    Pixel solar diameter         108
         Using M.O.A. per pixel enables subsequent sun to horizon pixel
    counts to be converted to M.O.A. for a designated zoom power.
    On Jul 3, 4:31�pm, Greg Rudzinski  wrote:
    > � � �A timed digital photo of the sun at low altitude provides enough
    > information to generate a line of position. For this task I use a
    > Canon PowerShot A560 set at 3 power optical zoom, 7 mega pixel, and
    > ISO 800. The high ISO setting helps reduce camera shake on a moving
    > platform.
    > � � �The digital image of the sun (using a shade filter held out in
    > front of the camera covering the sun) is downloaded to a laptop,
    > cropped, rotated, and enlarged so that the sun has at least a 20
    > millimeter screen diameter on the laptop. This limits altitudes to
    > about 6 degrees. Measurements are made using a ruler directly on the
    > laptop screen. The almanac diameter of the sun is a given at
    > approximately 32 minutes of arc. Knowing this will allow the ratio of
    > the laptop screen measurements to yield an altitude of the sun's lower
    > limb above the horizon in minutes of arc. Convert minutes of arc to
    > degrees and minutes. Correct for refraction, dip, semidiameter
    > (temperature and pressure if necessary). Perform normal sight
    > reduction for the GMT of the sun's photo to get an azimuth and
    > intercept.
    > � � �Preliminary trials from the beach for altitudes between 4 degrees
    > and 6 degrees show the average LOP within 4 nautical miles of GPS.
    > Precision is limited by rounding to the nearest millimeter on laptop
    > screen measurements.
    > EXAMPLE:
    > Semidiameter 15.73' (by navigation computer)
    > Full diameter 31.46'
    > GPS Latitude 34 09.8'N �Longitude 119 14.0'W
    > Height of eye 8 ft.
    > GMT 02H 44M 00S Date 07/03/08
    > Laptop measurements in millimeters:
    > Horizon to lower limb 226mm
    > Sun diameter 27mm (measured horizontal to horizon to avoid refraction
    > differences between upper and lower limb)
    > (226)(31.46) = 263.3' = 4 degrees 23.3' (hs) uncorrected
    > � � 27
    > Corrected and reduced to an azimuth 294.8 and intercept 0.4' away (by
    > navigation computer)
    > (not corrected for temperature and pressure)
    > The Nautical Almanac A4 table shows an additional +0.5' correction for
    > a pressure of 29.9 in. and a temperature of 70 F
    > iPHOTO was used to enlarge and crop sun images.
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