• Local Transverse Mercator

    From John Savard@21:1/5 to All on Mon Aug 12 13:22:45 2019
    Maybe this is a dumb idea.

    The "shape of the Earth", that is, the geoid, is more complicated than an ellipsoid. I remember when it was first mentioned that the Earth was pear-shaped,
    and now the geoid is seen to have quite a complicated shape.

    As far as I know, there are no geoid versions of map projections. All we have are
    ellipsoid versions.

    Different countries use different ellipsoids in making their large-scale maps, each one choosing an ellipsoid which best fits its territory. This is seen as a problem, as it leads to a mismatch between adjacent countries and so on.

    It's been proposed to solve this problem by having the whole world agree on one ellipsoid.

    However, the whole point of making large-scale maps based on the ellipsoid instead
    of the sphere is to make them *as accurate as possible*. So using a compromise ellipsoid is a step back.

    The following idea occured to me:

    what if each map sheet (or group of nine or 25 sheets sharing a common central meridian) were drawn on an ellipsoid that is the best fit to the geoid *in just that small area*. Then the next one over would be on a slightly different ellipsoid - if everyone did that, then the changes between one map sheet and the
    next one would always be small and gradual, instead of having huge mismatches at
    national boundaries.

    After all, this would be done based on a model of the geoid, so it wouldn't be necessary to do a thorough survey of the area in every map sheet to determine its
    best ellipsoid.

    John Savard

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  • From Alan Browne@21:1/5 to John Savard on Fri Aug 16 12:00:15 2019
    On 2019-08-12 16:22, John Savard wrote:
    Maybe this is a dumb idea.

    The "shape of the Earth", that is, the geoid, is more complicated than an ellipsoid. I remember when it was first mentioned that the Earth was pear-shaped,
    and now the geoid is seen to have quite a complicated shape.

    As far as I know, there are no geoid versions of map projections. All we have are
    ellipsoid versions.

    Different countries use different ellipsoids in making their large-scale maps,
    each one choosing an ellipsoid which best fits its territory. This is seen as a
    problem, as it leads to a mismatch between adjacent countries and so on.

    It's been proposed to solve this problem by having the whole world agree on one
    ellipsoid.

    Has it?

    By who?


    --
    "Even with the brain dead, the pig's heart keeps on beating...
    sort of like ... pick a Kardashian."
    -Anthony Bourdain, Parts Unknown

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  • From John Savard@21:1/5 to Alan Browne on Sun Aug 18 00:56:09 2019
    On Friday, August 16, 2019 at 10:00:22 AM UTC-6, Alan Browne wrote:

    Has it?

    By who?

    Darn. I thought it was, and I thought I read it somewhere.

    John Savard

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  • From Alan Browne@21:1/5 to John Savard on Tue Aug 20 20:32:50 2019
    On 2019-08-18 03:56, John Savard wrote:
    On Friday, August 16, 2019 at 10:00:22 AM UTC-6, Alan Browne wrote:

    Has it?

    By who?

    Darn. I thought it was, and I thought I read it somewhere.

    John Savard


    Right.

    In other news, Donald Trump was stupid, again[1], today, and only 60% of
    the USA noticed. His electoral college chances remain, alas, strong.

    [1] numerous times, tracking above his stupidity average for the past 5
    years.

    --
    "Even with the brain dead, the pig's heart keeps on beating...
    sort of like ... pick a Kardashian."
    -Anthony Bourdain, Parts Unknown

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  • From Just Wondering@21:1/5 to Alan Browne on Wed Aug 21 15:38:32 2019
    Alan Browne <bitbucket@blackhole.com> wrote in news:kJ-dnci86fevDMHAnZ2dnUU7- WmdnZ2d@giganews.com:

    Right.

    In other news, Donald Trump was stupid, again[1], today, and only 60% of
    the USA noticed. His electoral college chances remain, alas, strong.


    Hi Alan,
    Do you ever pull your head out of your ass?

    JW

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  • From Alan Browne@21:1/5 to Just Wondering on Sat Aug 24 12:35:30 2019
    On 2019-08-21 11:38, Just Wondering wrote:
    Alan Browne <bitbucket@blackhole.com> wrote in news:kJ-dnci86fevDMHAnZ2dnUU7- WmdnZ2d@giganews.com:

    Right.

    In other news, Donald Trump was stupid, again[1], today, and only 60% of
    the USA noticed. His electoral college chances remain, alas, strong.


    Hi Alan,
    Do you ever pull your head out of your ass?


    Never in there so doesn't need the remedy that you seem so familiar with.

    (Nice re-direct there - I fell for it, alas).

    --
    "Even with the brain dead, the pig's heart keeps on beating...
    sort of like ... pick a Kardashian."
    -Anthony Bourdain, Parts Unknown

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