[Qgis-user] NAD27 to NAD83

[Andre Joost]

Am 27.10.2017 um 21:25 schrieb Tyler Veinot:
>  We determined that
> it is because PROJ4 assumes gridshifts are always from X datum to WGS84,
> but NAD83 uses GRS80 so my question is, is there a way around this?
> Should I use a NAD27 to WGS84 gridshift and let QGIS reporject it to NAD83
> CSRS? Or is QGIS running on the notion that the 2 are coincidental?

All NAD83 CRS inside QGIS have +towgs84=0,0,0,0,0,0,0 , so NAD83 and 
WGS84 are treated as identical. You have to build a custom CRS if you 
want to apply a NAD83 shift from WGS84.

HTH,
André Joost