[Proj] How to transform between NAD83 HARN/HPGN and WGS84

[Aaron Friesen]

Richard, et al:

> -----Original Message-----
> > Do either NADCON or CorpsCon provide datum transforms between a
> > given NAD83 and WGS84?  The websites seem to indicate that they
> > are only for transforms among various NAD datums and I do not
> > know of a NAD83 variant that is truly assumed to be equivalent
> > to WGS84/ITRF00.  Please correct me if I am wrong on that.
> 
> I consider HTDP - Horizontal Time Dependent Positioning
> (http://www.ngs.noaa.gov/TOOLS/Htdp/Htdp.html) to be the authoritative
> source for ITRF <-> NAD83 conversions.

Thanks for the pointer.  I had actually stumbled upon HTDP after
getting some leads from this list late last Friday (sorry, don't
recall who gave me the pointer last week, but thank you to you as
well).

Based on that, my current plan of attack is to document/acknowledge 
the added error from each translation that is required.  The NGS
site indicates about how much additional error is introduced with each
translation.  The short answer (numbers are approximate) is that 
utilizing HTDP with CORS96 or later data and the transform will do
pretty much what I want.  For HARN areas, add 10 cm to best case
error.  For other NAD83, add 1 m to best case error.  For NAD27
(which is not currently on my list, but...), add 10 m to best case
error.

Thanks again to everyone,

Aaron