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Thread: Things to watch for-----

  1. #1
    Join Date
    Nov 1999
    Jacksonville,, FL, USA.

    Cool Things to watch for-----


    While finishing up the 3rd district of the CNO&TP, I occasionally move to the 2nd District
    for a hour or two. In doing this I encountered a small issue that I will explain how I
    handled it. Others may have their own methods.

    First, we can download elevation data from USGS and after minor massaging with
    VTBuilder, we can use DEMEX to generate the terrain. Secondly, we can use Google
    Earth to carefully digitize the route. Doing so introduces two errors at first. Parallax
    and shall we say, "trees in the way". The first is corrected by frequent use of the
    "R" key. The second will involve looking at older flyovers of the terrain in hopes of
    finding one where the leaves are off the trees --- but when we do, there is often a
    small error between "now & then". If the last point was on the center line of the
    track, or centered between tracks in double track, we may find a shift of a couple
    of meters one way or the other, so when I go to a different "flyover", I notice where
    the last digitized point fell, and correct by "precision eyeball" new points.

    Next, as we start to lay track, we often find that our digitized path does not precisely
    fit the generated terrain. For example, the track should be in the center of cuts or
    above the center of fills. I have included a image of the situation near mile 240 on
    the 2nd district where there is a fill, followed by a deep cut going south. There is
    also a old tunnel a few meters west (to the right) of the tunnel. At least the north
    portal is visible from passing trains. I know because as manager of track geometry
    inspection on the Southern, I passed this spot 132 times each way between 8/67
    and 8/78. The south portal was not visible. So in laying the track, I have shifted
    east or west a few meters in order to "fit to the terrain". A few miles to the north
    there is a situation where the old tunnel is beside and parallel to the track and it
    is close enough to spit on it while passing. Originally the "Rat Hole" had 27
    tunnels. The south most, #27 was removed many years ago & replaced by a cut.
    Many others were daylighted or bypassed over the years until in 1963 all but 4
    were removed.

    The "CC" in the image is just a point on the old line. The old line is not visible in
    Google Earth as such, but there is a line in the trees that suggests where it was.
    In some cases, I will be including both the old and new lines so that users can
    vicariously experience the old "Rat Hole".
    Attached Images Attached Images

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