API Reference > geometry-core > Bspline > BSplineCurve3d > evaluatePointAndDerivativeInSpan evaluatePointAndDerivativeInSpan Method Evaluate point and derivative vector at a position given by fractional position within a span. The derivative is with respect to the span fraction (NOT scaled to either global fraction or knot) evaluatePointAndDerivativeInSpan(spanIndex: number, spanFraction: number): Ray3d Parameter Type Description spanIndex number spanFraction number Returns - Ray3d Defined in bspline/BSplineCurve.ts Line 483 Last Updated: 12 June, 2024