ARCMAP-ELLIPSOID SURFACE

[ChuckTurlington]

Hello,

I am using ArcMap 10.3.

I have a question about the Ellipsoids surface and what it is intended to represent.  I see reference to the ellipsoid as approximating the earths surface but I also see the Ellipsoid concept as approximating the geoid surface.  So I have to ask: is the Ellipsoid intended to approximate the topography of the earths surface or the geoid surface ?

[DanPatterson_Retired]

Chuck some references with visuals from the help files

Geoid—Help | ArcGIS for Desktop 

The geoid, ellipsoid, spheroid, and datum, and how they are related—Help | ArcGIS for Desktop 

which also has a link to...

The official NGS GEOID Page 

But the first link with its image shows you the relationships visually

[ChuckTurlington]

Dan,

Thanks for your feedback.  If I understand correctly, the Ellipsoid is intended to simplify the geoid model according to the information you reference.  With that being said, does the Nad83 Ellipsoid "touch" or tie-to North America in  specific locations, like the Clarke model was tied to Kansas City ?

[DanPatterson_Retired · Accepted solution]

In that case you need to refer to the last link which is intended to provide more info.  I think they have moved to a more general representation that the 1927 version which was to a fixed point.

The links within Wikipedia may prove more useful, if not its description itself

North American Datum - Wikipedia