ARCMAP-ELLIPSOID - GEOID MODELS

[ChuckTurlington]

Hello,

I have been reviewing the basics of coordinate systems and trying to understand the role behind the Ellipsoid and Geoid.  I understand that the height difference between the ellipsoid / geoid, and the height between earths topography / geoid are related (h=H+N).  However, in my research I understand that a total station can be set to give elevation values on the Ellipsoid or the Geoid.  So I have to ask:  if the ellipsoid is an ideal shape of the earth with a simplified mathematical model, and I can work on the Ellipsoid grid to get my coordinates / elevations, why introduce the geoid at all?

[DanPatterson_Retired]

1-Mean Sea Level, GPS, and the Geoid 

http://www.ngs.noaa.gov/GEOID/PRESENTATIONS/2007_02_24_CCPS/Roman_A_PLSC2007notes.pdf 

Height Reference System Modernization | Natural Resources Canada 

plus hundreds more.  If you aren't doing survey grade coordinate collection, I can safely say that is not an issue.  If you are doing surveying, then you will have the equipment to collect the data appropriately and post-process it afterwards if needed.  As an example

http://www.esri.com/~/media/Files/Pdfs/partners/hardware/why-postprocess.pdf 

Tools and Applications | Natural Resources Canada 

[ChuckTurlington]

Dan,

Thanks a million for your feedback, I am enjoying the reading.  It appears the Geoid is calculated and the ellipsoid is made to best fit the geoid for a particular area, region or continent.  However, it seems the  geoid does not come into play unless calculating "mean sea level" heights (orthometric height - H), given the GNSS (Global Navigation Satellite System) topographic height (h) and subtracting the geoid height (N) using the relationship H=h-N.  Does my understanding sound correct ?

[DanPatterson_Retired · Accepted solution]

I would say yes... but I don't deal with the geoid in any way in my work.  I suspect it is of more concern to surveying.