beginner question - the real earth shape

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01-08-2011 08:43 PM
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Hello,

I read that the geoid is very close to the real earth shape(less than a meter off the MSL) and that it is at most 100m away from the WGS84 spheroid, then I saw such models where the MSL seems to be thousands of kilometers away from any spheroid, are those hugely exaggerated and inaccurate models or am I misunderstanding something? (from my understanding 100m shouldn't be noticeable and a good earth model should be a spheroid - almost a sphere - 22km difference between the spheroid axis shouldn't be noticeable as well).

Thanks for the help.

The geoid model:
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MelitaKennedy
Esri Notable Contributor
Hello,

I read that the geoid is very close to the real earth shape(less than a meter off the MSL) and that it is at most 100m away from the WGS84 spheroid, then I saw such models where the MSL seems to be thousands of kilometers away from any spheroid, are those hugely exaggerated and inaccurate models or am I misunderstanding something? (from my understanding 100m shouldn't be noticeable and a good earth model should be a spheroid - almost a sphere - 22km difference between the spheroid axis shouldn't be noticeable as well).

Thanks for the help.

The geoid model:
See original post for the graphic


Hi,

Yes, it's definitely been exaggerated. I seem to remember reading somewhere that the surface of the earth is smoother than the surface of a bowling ball (relatively). There are some numbers here:

http://www.geography.hunter.cuny.edu/tbw/GTECH201/notes/5.Earth.Coordinates.Grid.Coordinate.Systems....

on page 5.

Melita
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Thanks a lot :)
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