Get Orthometric Elevation from SparkFun Collection

[kratliff]

We use Esri Field Maps for GNSS collection. Our current workflow has a Arcade expression that runs each night which calculates the z to orthometric elevation in feet and populates an attribute field. When I run this on a SparkFun collection (versus the other GNSS devices we are using), the height is over 100 feet in error.

SparkFun provides ellipsoidal elevation. How do I get orthometric??

[rftop]

It’s the same calculation as used by any GNSS receiver, H = h - N.
Which NMEA sentence are you using for the metadata ?

what is the orthometric datum being used by the spark fun surveyor?

@PaulZC that all looks correct. Just watch the signs, the orthometric height is the ellipsoidal height less the geoid height. In many areas (including all 48 US states) the geoid height is a negative number, so it is effectively addition, and I confuse this often. H = h - N where H is the orthometric height, h is the ellipsoidal height, and N is the geoid height Here’s a good diagram: https://www.researchgate.net/figure/Rel … _273133676 Regarding applying the geoid model of your choice, you don’t really need to know what internal geoid model the ZED-F9P in the SparkFun product is using. Just back out whatever the internal geoid model is by using the separation provided in the $GGA message and you’ll have the ellipsoidal height. Then apply your own geoid model. The ellipsoidal height is: h = H + N Below is a $GGA snip from a project of mine in Virginia, USA. $GNGGA,184252.00,3811.5564944,N,07936.8396046,W,2,12,99.99,650.856,M,-33.810,M,0131*4A H=650.856m, and N=-33.810m. That H …