If you think of the figure as lying in the x-y plane, then its projection onto one of the axes has the same length no matter the orientation of the figure. One

If you think of the figure as lying in the x-y plane, then its projection onto one of the axes has the same length no matter the orientation of the figure. One nifty example of this is the Reuleaux triangle, which is related to the mechanics of rotary engines. http://en.wikipedia.org/wiki/Reuleaux_triangle http://en.wikipedia.org/wiki/Reuleaux_triangle