When detecting coincident points, the previous site [xsitex, xsitey] should be initialized to an illegal value (different from any potential valid input site). But [Number.MIN_VALUE, Number.MIN_VALUE] is a valid site, so use [undefined, undefined] instead.
When detecting coincident points, the previous site [xsitex, xsitey] should be initialized to an illegal value (different from any potential valid input site). But [Number.MIN_VALUE, Number.MIN_VALUE] is a valid site, so use [undefined, undefined] instead.