I have a cartographic project in Greece. The raster data go back in' 50s and '60s. That time the geographic system that was used was HATT (hellenic azimuthial). As a result the most of my raster file use that strange grid. The greek military geography service has published a method for the transformation of the hatt grid data to Greek Grid (2100). This method uses 2nd degree polyonomial function as you can see bellow
Where:
Αx and Bx are factors given by GMS
Χi, Yi the coordinates in HATT system and
Ei,Ni the result coordinates in Greek Grid (epsg 2100).
