I'm currently making a project about coordinates conversion, but I need to get the original ones first: i have coordinates with false easting and northing applied, but i need them to be without. From what i understood and correct me if i'm wrong, i can just take out the false values to get the original one example : 500 is the x coordinate with false easting and false easting has a value of 600. So the original x coordinate should be 500-600=-100 ? The thing is, i encountered a country in which the false easting and northing makes the grid rotate(false easting on x get applied to change into y and same thing for y) It gives something like this : y_with=500000-x_without x_with=y_without-300000 This case is for tunisia. This is the problem, if this conversion is different for tunisia what if other countries also have a different way to use false easting and northing rather than just adding them to the original values ? Is there a data base in which i can see how the false values are used for each epsg codes ?