This is a heuristic-- any number we use will be arbitrary. And since it's a floating-point calculation, using some maxint value just seems confusing to me. I don't think there's a problem with making it even bigger than 10k. But I wouldn't make it extremely big. At some point, the relatively small distance differences that we are looking for in the following few lines of code might get lost in precision error. Perhaps to make it less arbitrary we can set it to some multiple of the longest edge of the imaged volume?