[PROJ] proj8 and NAD27 <-> NAD83 transform

[Kirk Waters - NOAA Federal]

Even,
I decided to script out adding the transforms to the proj.db file so I can
automatically have my system add them when new proj.db files get released.
One thing I haven't figured out is how the extent is associated with the
transform. For 8971, I don't see anything in the helmert_transformation
table that looks close except the 'IOGP-Usa GoM' for the operation version.
EPSG.org shows the extent code for transform 8971 is 3357, which matches
what I find in the extent table, but I don't see where in proj.db that's
happening. The name for extent 3357 is 'USA - GoM OCS', so it doesn't match
the helmert_transformation entry for 8971. Apologies if I'm asking
something that's clearly laid out. I just haven't found the right docs yet.

Kirk


On Thu, Jun 3, 2021 at 6:49 AM Even Rouault <even.rouault at spatialys.com>
wrote:

>
> Le 03/06/2021 à 12:37, Kirk Waters - NOAA Federal a écrit :
> > Even,
> > Thank you very much, that's very helpful. It's along the lines of what
> > I was thinking was the problem, but I hadn't gotten far enough to
> > realize I could add an entry in the database. The other option is to
> > figure out the right EPSG code to pass to GDAL to pretend the
> > transform has already happened.
>
> If you use gdalwarp, you can lie a bit and set -s_srs EPSG:2273 to force
> "NAD83 / South Carolina (ft)" as the source CRS, and then you'll get the
> transformation to NAD27 using the CONUS grid.
>
> Even
>
>
> --
> http://www.spatialys.com
> My software is free, but my time generally not.
>
>
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