1. A method of finding and defining a plane, comprising: scanning in screen space a plurality of rows of a depth image; identifying a first deepest value in a first region of each row; identifying a second deepest value in a second region of each row; interpolating a straight depth line through the first deepest value and the second deepest value for each row; fitting a first straight boundary line using a subset of first endpoints of the straight depth lines; fitting a second straight boundary line using a subset of second endpoints of the straight depth lines; and defining the plane through the first straight boundary line and the second straight boundary line.