Post by C.M.German
Googleing gave me this.......
Maybe it will help you.
Thanks, I had already read that one, it is good but it primarily refers
to Geoid96 which, although based somewhat on EGM96, is not the
same. Figure 3 in that article does show a mean offset of NAVD88
with a global geoid model, but I am uncertain which global geoid it
refers to. It might be EGM96 given a discussion of the Rapp(1996)
article found here:
EGM96 is a global geoid that uses the WGS84 ellipsoid as a
horizontal datum. See:
A good discussion of EGM96 can also be found in the DOD WGS84
From the GEOID96 FAQs found at this page:
"Our current estimate of the NAVD 88 vertical datum offset is 31.4 cm below
the current best estimate of the Earth's best-fit global geopotential. (A
good news: the NAVD88 offset seems to be a constant offset; the same
throughout the conterminous United States.) "
But, again I don't know what global datum they are referring to.
As far as I understand it, NAVD88 is not referenced to an earth centered
geoid datum, which makes it more difficult to relate to other datums that
I suspect there is no easy conversion between EGM96 heights and NAVD88,
but the paper you found is good for understanding how you might go about
it. But, I don't want to reinvent the wheel, especially since I am no expert