Secure Sketch Construction
One standard solution is described in the following research paper:


Robust discretization, with an application to graphical passwords.  Jean-Camille Birget and Dawei Hong and Nasir Memon.  eprint 2003/168.


That paper shows how to deal with the problem that the user's second point might be close to, but not exactly the same as, their original point.  In other words.... exactly your problem.

There might be more recent work on this problem.  You could do a literature search, starting from the above paper (e.g., looking at other papers that cite it) to see whether there are other better solutions.