NAD & NAVD

[mgonzales.224492]

does anyonekow if there is a difference between NAD 83 & NAVD 88...

[sinc]

A huge difference.

To start, one is a horizontal datum, the other is a vertical datum.

[sinc]

Or perhaps I should say that one is a reference ellipsoid, while the other is a vertical datum.

NAD 83 will give you ellipsoid heights, but to be useful, those still need to be converted to an orthometric height, which might be in NAVD 88.

I have a paper where I go into a fair bit of detail about precisely what NAD 83 is. I don't really talk about NAVD 88 in this paper, but it might be helpful with understanding NAD 83. It's the "Working with Grid Coordinates" paper found here:

http://www.ejsurveying.com/Articles.aspx