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I usually write questions and answers on https://gis.stackexchange.com.

English is not my first language, and every time I have to write any of these terms I come back into doubt about which of the two corresponds.

A geodesic, can be understood as the shortest path (contained in a curved surface) between two points. (https://en.wikipedia.org/wiki/Geodesic)

But I have the problem when I have to refer to something related to geodesy (https://en.wikipedia.org/wiki/Geodesy), e.g., "geodesic distance", "geodesic calculations", "geodesic math", "direct geodetic problem", "geodetic datum", "geodetic coordinates".

I don't know which of the two terms I should use.

What is specifically the use that should be given to the terms "geodetic" and "geodesic"?

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  • I'm a native speaker and a software engineer with significant GIS experience, and I often wonder the same thing. I do think this question is a better fit for gis.stackexchange.com as it's really about technical jargon, not the English language itself.
    – TypeIA
    Nov 28 '19 at 22:59
  • @TypeIA Thank you for the response. The question was raised in the chat room there, but the room is not very busy. I will make sure that it is not considered off topic if it is posed as a question on the GIS SE site. It is likely that there would be read by people focused on the subject, but I thought the topic was more suitable for this site. Nov 28 '19 at 23:33
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I too frequent the GIS Stack Exchange and use English as my first language in Australia.

I was not sure of the answer so I used search terms of "adjective geodesy" to find this Dictionary.com definition for geodetic:

geodetic [jee-uh-det-ik]

adjective

  1. pertaining to geodesy.
  2. geodesic.

It looks like geodetic and geodesic mean the same thing and are equally valid to use. My preference is to use geodetic as the adjective of geodesy.

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Geodesy

Geodesy (from greek γεω- geo- and δαι ́ζω split) relates to the study of Earth shape.

A geodesic line is a shortest possible path on an ellipsoid like Earth, what we commonly call a great circle, though this word only applies to a perfect sphere.

Laplace first defined the geodesic line as ligne géodésique:

Nous désignerons cette ligne sous le nom de ligne géodésique.

Confusion

A confusion was created a long time ago when the geodesic line concept was translated into English by English scientists like Hutton who proposed a translation of his own:

A line traced in the manner we have now been describing, or deduced from trigonometrical measures, by the means we have indicated, is called a geodetic or geodesic line.

This gave:

Geodetic datum

There is a special case where the word geodetic is the only one used. A geodetic datum is a datum used in geodesy and other fields. The best known being WGS 84 used for all GNSS techniques, WGS meaning World Geodetic System.

For other uses, geodesic and geodetic are synonymous, the result of this double translation.

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