I’d appreciate input on the process for identifying the Ellipsoidal Height for a known set of coordinates. I could be overcomplicating this, and am probably overlooking something, but I’ve spent a bunch of time and don’t quite nail it with the tools I am using, so I thought I’d seek input from this experienced group.
Here is a known monument as an example, in Rockwall Texas, from their GIS site.
Latitude N 32° 56’ 43.44684"
Longitude W 96° 28’ 20.68730"
Date_Recorded September 6, 2017
Projection NAD 1983 (2011) TEXAS NORTH CENTRAL ZONE (4202)
“Please note that, although either orthometric or ellipsoidal heights can be used as inputs to NCAT, at this time NCAT does not convert between orthometric and ellipsoidal heights. Only orthometric-to-orthometric and ellipsoidal-to-ellipsoidal height transformations are currently possible in NCAT”.
You can also use the NGS geoid height processor for various flavors of “N”.
h= H + N
where “h” is the ellipsoid height
“H”= orthometric height
“N”= geoid height (various models)
The formula above is the simplified version and does not take into consideration deflection of the vertical and gravimetric effects.
In your case above, you want to determine the ellipsoid height. From the formula above, we can determine the height.
From the NGS computation, it gives a value of -25.478m, 0.046m error at 95% confidence level. The error is based on the density of passive stations with orthometric heights determined by differential leveling.
Output from GEOID12B is in meters -25.478m. We need “ftUS” though. 1m = 3.280833333 ftUS