topic ARCMAP-ELLIPSOID - GEOID MODELS in ArcGIS Online Questions

ARCMAP-ELLIPSOID - GEOID MODELS

ChuckTurlington — Sun, 16 Oct 2016 19:30:04 GMT

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?

Re: ARCMAP-ELLIPSOID - GEOID MODELS

DanPatterson_Retired — Sun, 16 Oct 2016 19:39:29 GMT

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

Re: ARCMAP-ELLIPSOID - GEOID MODELS

ChuckTurlington — Wed, 19 Oct 2016 12:26:45 GMT

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 ?

Re: ARCMAP-ELLIPSOID - GEOID MODELS

DanPatterson_Retired — Wed, 19 Oct 2016 14:35:10 GMT

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.