At the points where a line cuts the sides of a Triangle , perpendiculars to the sides are drawn, forming a Triangle similar to the given Triangle. The two triangles are also in perspective. One point of intersection of their Circumcircles is the Similitude Center, and the other is the Perspective Center. The Circumcircles meet Orthogonally.
See also Circumcircle, Orthogonal Circles, Perspective Center, Similitude Center
Johnson, R. A. Modern Geometry: An Elementary Treatise on the Geometry of the Triangle and the Circle. Boston, MA:
Houghton Mifflin, pp. 258-262, 1929.