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    Re: Timing Upper Limb Sunset by Camera
    From: Bill B
    Date: 2015 Apr 07, 16:47 -0400

    On 3/28/2015 9:06 PM, Greg Rudzinski wrote:
    > You may want to try using Neptune's Net position as an assumed position
    > to generate an azimuth and intercept. The intercept should be less than
    > a mile.
    Taxes filed, so it was time to quit having fun and get back to toiling
    away on your suggestion :-)
    Plotting in Google Earth turned out to be a hassle. When I added a
    placemark its displayed lat and lon drifted depending on zoom level.
    Adding lines is also a bit bizarre. It does seems to deal OK in nautical
    miles or feet, but does not adjust lateral lines for latitude if using
    the degrees or arc seconds option. In long range testing it does
    generate the great circle route, and properly reports a line bearing at
    or close to the initial great-circle course. To avoid attaching too many
    images, I'll follow up on that in a subsequent post.
    The long and short time-sight COP/LOPs were generated assuming a 50'
    height of eye. Bill's Final location is a position (this time on the
    coast) where a 50' height-of-eye Ho matches the USNO Hc.
    Intercepts were 1!2 and 1!9 depending on height of eye. As the azimuth
    of 273.1d was close to lateral, I plotted by multiplying feet or
    nautical miles by the cosine of 34d 03'.
    By the time I was done, I noticed the anchor points for the intercepts
    were a bit west of the road in front of Neptune's Net so added the
    adjusted markers.
    In the past I have found Google earth can be accurate withing 10 meters
    at times, and over 200 meters off other times. It also seems to be a bit
    sketchy on elevation.
    As a sanity check I plotted the intercepts in DeLorme Topo. Much easier.
    I can enter the lat/lon starting point of a line and it stays anchored
    where I placed it. Also beneficial are the contour lines for elevation.
    Zeroing in on height of eye (and referencing "Surely You're Joking Mr.
    Feynman" as a favorite book) were you headed up the coast for a
    reflexology session at Esalen Institute, or on the way home when you
    made the observation? (which side of Neptune's Net?) ;-)
    Off topic, but I still have a violet colored T-shirt from my visit to
    Esalen the early 80's. Before their revisionist history, the entire
    grounds and buildings were clothing optional, and the hot tubs clothing
    free. I can prove it. No Photoshop then, just negatives and prints with
    Back on topic, DeLorme misplaced Neptune's Net at the next intersection
    down the coast (Tonga St.), so Google Earth's imagery was handy in
    locating your watering hole as an AP.
    All said and done, a good learning experience, especially in getting a
    better handle on the pitfalls of doing precise/accurate work with Goggle
    Now about that pint...





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