Talk:Geoid

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Contents

[edit] Misc

  • Gender specific pronouns*

The earth has no gender, so is it necessary to call it a she ?


I'll change the article over to using gender-neutral terms

Thanks for adding the link to Physical geodesy!

Martin Vermeer

I had in fact for some time been missing some explanation of "Geoid".

S.

[edit] Wrong character

Hi, I think there's an error in the formula: you write "φ and λ are geocentric latitude and longitude respectively", but nowhere in the formula can I see any φ ...

Laurence Vanhelsuwe

The problem is that Wikipedia:TeX markup permits simple TeX characters to be displayed as HTML characters, thus in a different font, which here appears to change the character, even though both are phi. Thus I changed <math>\phi</math> φ to <math>\phi\ </math> \phi\ by adding the math text space '\ ' immediately after the math character, which forces it to be rendered as a PNG character, just like those in the formula. — Joe Kress 07:16, Apr 17, 2005 (UTC)

[edit] Counting Coefficients

Greetings!

When you count the geopotential coefficients at the end, you get 130,317. You should probably mention what maximum degree (n) you used and why you chose that value. After all, in principle, n is infinite.

Oh, and if you're interested, here's a quick and visual definition from the project I work on (GRACE): http://www.csr.utexas.edu/grace/gravity/gravity_definition.html

Take care! Jennifer Bonin

I'll try to clarify this. After all, there are new models in the works with degree=order=2160 (over 4 million coefficients), good to 1/6 degree. MFago 14:46, 5 April 2006 (UTC)

[edit] References and Intro

Was it a good idea to split the top into the short intro and a new "description" section? More closely follows other Wikipedia articles, so I made this change. Also, this article could really use more citations. Unfortunately, I haven't quite figured out the "cite" template... MFago 15:43, 5 April 2006 (UTC)

[edit] Centrifugal Force

Hi, I can't find the answer to this anywhere!

Does the geoid take into account centrifugal force from the Earth's rotation? If so, would it be incorrect to refer to it as a mathematical figure of the gravity field alone? And if not, would it be incorrect to say that the mean sea level assumes the shape of the geoid?

Or is all of this too miniscule to make any difference?

There is not actually "a" geoid, but rather many different variations depending on whether or not one accounts for tides, etc. I do believe that it usually does account for rotation. Note that the equation given in the article is not for the geoid itself, but for the (non-rotational part of the) potential. Computing the geoid is rather more involved. I'll see if I can relocate my reference on this (at NIMA or a related site), and perhaps add more detail to the article. Also see Physical geodesy and Geodesy. The reference text the end of Geodesy is excellent and covers most of the details. MFago 23:21, 1 June 2006 (UTC)
Link added to above reference: No such thing as "The" EGM96 geoid, and tried to clarify a bit. Really needs more detail -- it's a complex subject, and I'm not entirely fluent. MFago 23:33, 1 June 2006 (UTC)

[edit] Broken Links

I just saw that all of the NGA links are broken. I cannot locate any of this data on the new "enhanced" site -- it appears to be unavailable? MFago 23:52, 1 June 2006 (UTC)

Fixed. They simply changed all *.htm to *.html, and their search engine was of no help. MFago 00:04, 2 June 2006 (UTC)

[edit] Geoid Picture

Unfortunately the picture of the Geoid (actually the geoid undulation) that used to be on this page was evidently taken from the GRACE website without proper permission. Anyone have access to another similar graphic that would be useable here? The raw data for the EGM96 geoid (less detailed than GRACE, but still illustrative) is available at: NGA EGM96 data (labeled as "Geoid Height File"). Matlab can easily make a similar plot from this data, but I do not have access to this software. Anyone able to help, or have another idea?MFago 14:36, 2 June 2006 (UTC)

[edit] Possible image error

Shouldn't the local plumb lines in the image in the Description section be orthogonal to the geoid? Shinobu (talk) 12:42, 1 February 2008 (UTC)