Click here to open a Pedal Triangle construction in GSP. Notice that when the pedal point is the orthocenter, the pedal triangle is an orthci triangle. Thus, the pedal triangle intersects the original triangle at the feet of the altitudes. Experiment with the GSP construction to see what happens if the pedal point is one of the other centers of the triangle.

Also, take a look at a GSP script for a pedal triangle.