[MetaCRS] Coordinate offset after transformation from 4267 to 4326

[Jody Garnett]

Just wanted to report back to this email thread, although I was never able
to determine quite what PROJ4 was doing but we were able to use a series of
points to make an educated guess:

The fix, at least for me, was to define a customer
*epsg_operations.properties* file that combined the grid-shift transform
(from NAD27 --> NAD83) and the shift from NAD83 --> WGS84):

      4267,4326=CONCAT_MT[ \
         PARAM_MT["NADCON", \
           PARAMETER["Latitude difference file", "conus.las"], \
           PARAMETER["Longitude difference file", "conus.los"]], \
         PARAM_MT["Molodenski", \
           PARAMETER["dim", 2], \
           PARAMETER["dx", 0.0], \
           PARAMETER["dy", 0.0], \
           PARAMETER["dz", 0.0], \
           PARAMETER["src_semi_major", 6378137.0], \
           PARAMETER["src_semi_minor", 6356752.314140356], \
           PARAMETER["tgt_semi_major", 6378137.0], \
           PARAMETER["tgt_semi_minor", 6356752.314245179]]]

This has output between GeoServer and QGIS lining up sufficient for the
application I am working on.
--
Jody

--
Jody Garnett

On 26 May 2016 at 12:12, Jody Garnett <jody.garnett at gmail.com> wrote:

> Thanks for your help Martin, I will see what I can do.
>
> I would still like to learn if there is a way to check what PROJ4 is up
> to, as this is the first time I have worked with grid shift files I have no
> confidence I am doing so correctly.
>
> --
> Jody Garnett
>
> On 26 May 2016 at 11:19, Martin Desruisseaux <
> martin.desruisseaux at geomatys.com> wrote:
>
>> I forgot to said: in order to verify what GeoTools actually used - i.e.
>> whether it used the grids or the TOWGS84 parameters, and in the later
>> case which parameter values -, a System.out.println(theMathTransform)
>> would help.
>>
>>     Martin
>>
>>
>
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