[MetaCRS] Coordinate offset after transformation from 4267 to 4326

[Martin Desruisseaux]

Thanks for the update, this make sense.

For info, EPSG geodetic dataset defines a transformation from NAD27 to
NAD83 using the "conus" files as you did, followed by a transformation
from NAD83 to NAD83(HARN) (one of the new NAD83 definitions created
after the original one) one the assumption that NAD83(HARN) is
equivalent to WGS84 within the accuracy of the transformation. The later
transformation is using other grids depending on the geographic area (I
didn't saw a grid for the whole US for the NAD83 to NAD83(HARN) part,
but maybe I didn't searched hard enough).

    Martin


Le 14/06/16 à 01:15, Jody Garnett a écrit :
> 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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/metacrs/attachments/20160614/48968ea6/attachment.html>