It depends on what you are asking for.
If for the KCWO, there will be either paint or string to clearly delineate the OB.
If for league, the league director should clearly call which way it plays.
If for casual, just agree in advance. Typically a good rule is that whatever you agree on goes and if there is some doubt give the benefit of the doubt to the player (i.e. if it is highly questionable if in or out play it as in).