[Proj] HARN/HPGN

[Richard Greenwood]

On Fri, Aug 20, 2010 at 7:37 PM, Frank Warmerdam <warmerdam at pobox.com> wrote:
> Folks,
>
> At the request of a client, I have developed some tools to translate
> between the .los/.las format used for datum grid shift files distributed
> by NOAA for NADCON to NTv2 for convenient use with PROJ.4.  This was
> done primarily to make use of the NOAA HARN datum shift files practical.
> This has gone ok.
>
> However, now that I look at utilizing the data I find that there are
> distinct HARN grid shift files for each state.  On examination I find
> that they overlap, and that the overlapping areas do not agree.  I read a
> bit of material from NOAA/NGS which seems to suggest each state does it's
> own thing.
>
> When I look in the EPSG database, there seems to be only one GCS mentioning
> HARN which is EPSG:4152 NAD83(HARN).
>
> The online HARN conversion tool on the NGS site requires you to pick a
> state grid file.
>
> So my question is basically - is there really a distinct HARN datum for
> each state?  Does it make sense to treat HARN as a datum, or should it be
> treated as ~52 datums?

I consider them to be ~52 different datums and the user needs to
select them for them self. It's not something that can or should be
done automatically.

I am very happy to see this addition, thanks!

Rich

-- 
Richard Greenwood
richard.greenwood at gmail.com
www.greenwoodmap.com