The number of control points shall be at least three.vectorAtStart is the unit tangent vector at the start point of the spline. vectorAtEnd is the unit tangent vector at the end point of the spline. Only the direction of the vectors shall be used to determine the shape of the cubic spline, not their length.interpolation is fixed as "cubicSpline".degree shall be the degree of the polynomial used for the interpolation in this spline. Therefore the degree for a cubic spline is fixed to "3".The content model follows the general pattern for the encoding of curve segments.
<element name="CubicSpline" type="gml:CubicSplineType" substitutionGroup="gml:AbstractCurveSegment"><annotation><documentation>The number of control points shall be at least three. vectorAtStart is the unit tangent vector at the start point of the spline. vectorAtEnd is the unit tangent vector at the end point of the spline. Only the direction of the vectors shall be used to determine the shape of the cubic spline, not their length. interpolation is fixed as "cubicSpline". degree shall be the degree of the polynomial used for the interpolation in this spline. Therefore the degree for a cubic spline is fixed to "3". The content model follows the general pattern for the encoding of curve segments.</documentation></annotation></element>