UNDERSTANDING SHAPES (Including Polygons)
161. Curves & Regions · Open, closed, and simple closed curves
P is inside when distance from center < radius; P is outside when distance ≥ radius.
A closed curve forms a complete loop with no endpoints (like a circle). An open curve has two distinct endpoints that do not meet (like an arc). A simple closed curve is a special type of closed curve that does not intersect itself — the boundary is a single continuous loop.