Boundary curve of circles centered on an astroid
Exploration of the boundary curve of the region filled by circles centered on an astroid
1. The parameter d is the offset distance
2. The red and green curves and their union are envelopes of the family of circles of radius d centered on the astroid.
3. The boundary curve of the region filled by the circles (in orange) is the union of arcs of the envelope and of arcs of circles centered at the cusps of the astroid.