1. Mick West

    Mick West Administrator Staff Member

    waltis curve simulator.

    Walter Bislins has created a very useful tool for visualizing what things should look like from certain positions, and with certain camera settings, on the Globe Earth, or on a hypothetical Flat Earth.

    The Simulator includes recreations of classic and modern experiments and observations including the Bedford Level, the Pontchartrain Power Lines and Causeway, and the Chicago Skyline. You can stop the simulation at any point, and examine the scene and the settings used. Here's a (non-interactive) animation of the Bedford Level experiment.


    I'd encourage anyone interested in the topic to play around with the various settings and watch all five demos.

    Simulator with discussion:

    Simulator alone:
    Last edited: Jul 15, 2018
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  2. Antrax

    Antrax New Member

    I've used this simulator for high altitude footage I found on Reddit/Youtube, which according to the author was taken at an altitude of 115,000feet/35km with a Canon Powershot SD880 set to 35mm film equivalent of f=40mm.
    I'm not really good with photoshop and had to do it on my smartphone, so it doesn't look as good as the examples made by Walter. Anyway, here's what I got: videoto_2017.08.23_14.26.56.

    Reddit: https://www.reddit.com/r/pics/comments/4fyiks/a_year_ago_my_brother_and_i_launched_a_high/

    Source: https://m.youtube.com/watch?v=tI6alFMD79I
    Last edited by a moderator: Aug 23, 2017
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  3. Enricks

    Enricks Member

    So in the Bedford Level experiment the middle pole was totally visible, but below the line of sight and above the distant mark?
  4. Mick West

    Mick West Administrator Staff Member

    "Line of sight" can refer to any line, but I think you mean "eye level" - i.e. a horizontal line from the telescope, perpendicular to the vertical direction at the telescope?

    From any given position the water surface is going to seem to "drop" away from the horizontal plane (it's like you are standing on top of a very large ball). So the middle pole is going to be below that plane, and the distant bridge will be below that.

    So if you take a line of sight from the telescope to the distant bridge, then the middle marker will appear above that.
  5. Enricks

    Enricks Member

    Yes, sorry for my slip of tongue there: I meant eye level. I found that odd because at sea level the "drop" should be 0, like you showed in your "horizon dip" demonstration, so both the horizon and the pole should not show any drop. I don't know if I'm misunderstanding something (almost certainly yes lmao).
  6. Mick West

    Mick West Administrator Staff Member

    The side to side visual "drop" of the horizon is zero at sea level. But that's a totally different thing to the curve of the Earth away from you.

    And here the telescope is not at the water level. It's like 12 feet above the water, looking at things that are 3 and six miles away. The thing 3 miles away will be 6 feet below the horizontal plane passing through the telescope, and the thing 6 miles away will be 24 feet below that plane.

    The key thing though is the "bulge", which is 6 feet over 6 miles. i.e. the middle marker will be six feet higher than a line of sight between the end points (assuming all are the same height above the water)
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  7. Enricks

    Enricks Member

    I asked this because in the animation you provided above, the horizon seems to be dropping below eye-level (i.e. the crosshair), but maybe I'm making a mistake somewhere.
  8. Mick West

    Mick West Administrator Staff Member

    No that's correct. The horizon is always below eye level if your eye is above the water level. Not a lot when you are close to the water level, but the effect is magnified here because of the high zoom.
  9. Rory

    Rory Senior Member

    I'm not quite sure what you mean by "drop"? Or why it should be zero?

    Also, to clarify, it's not so much about measurements at "sea level" - for example, doing calculations for a view across a high elevation mountain lake, you'd want to know the height above the water, rather than above sea level.

    Though I think you get that already; thought I'd mention it just in case.
  10. Enricks

    Enricks Member

    Never mind, Mick already gave me a satisfying answer :p

    EDIT: btw, by "drop" I meant horizon dip.
    Last edited: Aug 27, 2017
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