Within the coordinate system tools common to MicroStation, OpenCities Map, Descartes and other platform based Bentley software we must specify both a datum and a transformation as associated to a given GCS definition.

As often there can be many different datum transformations associated with one geodetic datum, these are accounted for as variants on the base definition. 

When storing to georeferenced raster image formats such as iTIFF or Geotiff, the variant definition cannot be specified and thus the base GCS is written to the raster file header.  This is working as designed.  As the definition cannot be stored, raster reprojection to the variant is not a viable solution. 

In these cases the user is limited to accommodating the variant within the raster attachment settings via either:

Specifying the variant as the coordinate system via the raster's attachment settings
or
Utilizing the Inherit GeoCS from Model setting, when the desired variant matches the model's GCS definition.

The limitation and remediation are demonstrated in the following video, utilizing EPSG:3003 (base) and EPSG:3003-A (variant) coordinate systems, exhibiting a shift of ~53.76 meters.

 

Alternate workflow:

In situations where it is cartographically acceptable, the observed shift between the base and variant can be manually applied to the raster image.

The result is then 'accurate' definition of the image as the base coordinate system (3003) in lieu of using the variant (3003-A).

 

Pursuing this approach, we must also consider that Raster Manager will prevent modification of raster attachments.

Attempting to do so will result in the inability to complete the move operation and may result in the message:

 

Raster image is currently reprojected

The operation could not be completed. Resolve this by changing one of the following settings:

Raster "Inherit GeoCS from model" is turned OFF - Must be ON

Raster Coordinate System is different than "Inherited from Design File"

In the following video, we demonstrate application of the shift to the image.

A copy is made of the source image, and both source and copy are attached.

The shift is applied (via 'Inherit GeoCS from Model...') to one image, the comparison then allows delineation of the shift represented by a line element.

Raster image is currently reprojected is avoided by shifting the image while Inherit GeoCS from Model  is engaged for the target image.

The modified raster image is then attached demonstrate the intended result.