I'm surprised to see this, as the process would seem to be pretty straightforward (determine LLH, then apply geoid model). But I suppose there are enough moving parts involved that the process could get derailed by even a minor change in just the right place.
I do not know how the orthometric height is to be determined in OPUS Projects. That said, the process described in the NGS Orthometric height determination guidelines includes an orthometric height adjustment after the ellipsoid height adjustment.
In other words, after identifying and addressing problems raised by the minimally constrained adjustment you perform a fully constrained adjustment holding published latitude, longitude and ellipsoid heights. After dealing with possible problems with constraints, another adjustment step is performed holding points with valid NAVD 88 heights.
This process allows the determined heights to better fit the network rather than merely applying the ellipsoid-geoid separation to the horizontal position.
Automated processing tools given rigorous parameters e.g. rejection criteria for constraints can yield good results. Unfortunately when it comes to NAVD 88 points expecting good agreement with published values can be problematic.
Hope this contributes,
DMM
GeeOddMike, post: 326704, member: 677 wrote: I do not know how the orthometric height is to be determined in OPUS Projects.
I've assumed that the automated Projects process wouldn't allow for the specification of ortho height constraints that aren't part of the current geoid model, but maybe that's not correct. More research needed!
One of my issues with OPUS Projects is that you can't fix the orthometric height of CORS stations. Several of our CORS Stations have a 1st or 2nd Order Orthometric Height on the ARP from direct leveling. When you are doing adjustments in Projects it only uses the Elipsoid Height of the CORS Stations from the GPS height. It is only a mm or two but why not get it right. I have a work around for it but it takes a lot of careful pre planning and is time consuming.
