I am not sure what you are asking? Do you want to find 49 points on a wafer to take your measurements from? Or do you want to determine the X Y coordinates for data already measured on a wafer? Could you be more specific in what you need.
Do you have the Arc(Theta) location from center for each of the points? That is, what is the form of the positional data from the metrology tool? Or, like many fabs, do you just have a pattern of where the points are in die X and Die Y values?
If you have that information, we should be able to solve your problem.