one option is alwaysw to write some adaptive / iterative algorithm and try and try until the original functional returns values, for which you want to know the inverse. the inverse is just your best guess.

the mathematic way of solving is to write down the function and solve for another variable.
mathematica or one of these open source maths programs written in common lisp should be able to solve that in a second. as soon you wrote down the task to solve properly…

excellent, the algorithm seems to fit the problem very well, as the translated coordinates are close to the original ones.
maple gave me a 2 pages long expression for tthe inverse function, that was not applicable…