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

[Aaron Friesen]

Everyone,

I checked the archives for the past year and did not find an
answer to this.  Google did not provide me with any leads
either.

I have data in NAD83 HARN for Colorado.  I need to take the
data into the field as WGS84, update it/add to it, and get
it back as NAD83 HARN for Colorado.  The data I am collecting
has sub-foot accuracy, so "close" is not good enough.

The information on the grid files does not address the
HARN/HPGN question.

Is this type of transformation with the accuracy I need
possible with Proj?

Are HARN grid files available or are towgs84 settings defined
for the various HARN areas?

Or am I stuck looking for an alternative, commercial solution?

Thank for your assistance.

Aaron