the ellipse and its evolute
and the distance problem:
updating Apollonius

by Frederick Hartmann and Robert Jantzen [2004]

This project is a fond memory of my friendship with Fritz Hartmann who left us too soon in 2021.

Fritz Harmann

The ellipse plot with its evolute and family of normal lines is a pretty design. Extracting only the simple figure from the article is done here:

ellipse evolute red and blue   ellipse evolute normals black&white Evolute-Institute logo