[Qgis-user] NTV2 Grid Shits

[Andre Joost]

Am 24.10.2017 um 22:42 schrieb stevejking:
> Tyler,
>   NAD27 and ATS77 don't seem to share the same ellipsoid.
> spatialreference.org lists ATS77 as
> +proj=sterea +lat_0=47.25 +lon_0=-63 +k=0.999912 +x_0=700000 +y_0=400000
> +a=6378135 +b=6356750.304921594 +units=m +no_defs
>
> It's missing a +towgs84= or +nadgrids= BUT Notice the ellipsoid a and b
> parameters do not match the NAD27 clarke66 ellipsoid. So a nadgrids shift
> file for NAD27, will not work for ATS77.
>

See 
https://knowledge.safe.com/articles/815/datum-and-grid-shift-for-canadian-provinces-new-br.html 
and 
https://knowledge.safe.com/articles/789/where-to-source-canadian-grid-shift-files-not-incl.html

HTH,
André Joost