Fuzzy Creep/Coordinate Drift
Digital computers have finite word lengths
- The set of numbers that they deal with is finite
- They cannot perform real number arithmetic
This complicates the problem of determining whether or not a point is inside or outside an interval or region (polygon)
Coordinate transformations can be exact only in rare cases – there is always some combination of round-off and algorithm error
- After a sequence of computations, these errors may increase (although they are generally very small) – this is sometimes called coordinate drift or fuzzy creep
- In a particular application domain, the developer must be aware of this possibility and institute the appropriate actions
Examples
- Using a GUI, a player places a combatant just inside a building. Due to round-off, the internal model representation of the combatant may be outside the building, and can be acquired and attrited. If polygonal regions are involved, and the original point is in another coordinate system, coordinate drift can cause this kind of behavior
- Sequences of coordinate transformations may not be reversible near (e.g., UTM) zone boundaries