OB = 1
BA is a straight line perpendicular to OB
the arcs in green are segments of circles, with a common center O
the lines in blue are extensions of straight lines with their
origin at O
Consider a point moving from B to A along the segments Bl, lp, pl2, etc.
alternating between movement in a straight line and a circular arc. The straight lines
(blue) could be thought of as segments of linear distance. The arcs (green) could be
thought of as segments of perpendicular distance.
If the segments of linear distance are added up, the sum is defined as a linear
distance, or x-length, of the line BA relative to 0.
The sum of the perpendicular segments are defined as a perpendicular
distance, or y-length of BA, relative to 0.