Three useful geometric properties, with their concrete consequences here, are:
- Endpoint interpolation. and . The middle control point is a handle, not an interpolated point: , so the curve never reaches .
- Endpoint tangents. and . Thus the tangent lines are parallel to the first and last sides of the control polygon, respectively; both endpoint derivatives are nonzero.
- Convex-hull containment. The three Bernstein basis weights are nonnegative and sum to one on . Every is therefore a convex combination of , so the entire Bézier curve lies in their filled triangle.
These give the compact answerThe same sum-to-one calculation also explains affine equivariance of a geometric basis: applying an affine map to the handles applies that map to the curve.
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