topic ARCMAP-ELLIPSOID SURFACE in ArcGIS Online Questions

ARCMAP-ELLIPSOID SURFACE

ChuckTurlington — Sat, 15 Oct 2016 14:52:07 GMT

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 ?

Re: ACRMAP-ELLIPSOID SURFACE

DanPatterson_Retired — Sat, 15 Oct 2016 16:07:49 GMT

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

Re: ACRMAP-ELLIPSOID SURFACE

ChuckTurlington — Sat, 15 Oct 2016 23:33:13 GMT

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 ?

Re: ACRMAP-ELLIPSOID SURFACE

DanPatterson_Retired — Sun, 16 Oct 2016 01:28:01 GMT

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