<element name="vectorAtStart" type="gml:VectorType">
  <annotation>
    <documentation>"vectorAtStart" is the unit tangent vector at the start point of the spline.</documentation>
  </annotation>
</element>

<element name="vectorAtEnd" type="gml:VectorType">
  <annotation>
    <documentation>"vectorAtEnd" is the unit tangent vector at the end point of the spline.</documentation>
  </annotation>
</element>

<complexType name="SimpleCubicSplineType">
  <annotation>
    <documentation>Cubic splines are similar to line strings in that they are a sequence of segments each with its own defining function. A cubic spline uses the control points and a set of derivative parameters to define a piecewise 3rd degree polynomial interpolation. Unlike line-strings, the parameterization by arc length is not necessarily still a polynomial. The function describing the curve must be C2, that is, have a continuous 1st and 2nd derivative at all points, and pass through the controlPoints in the order given. Between the control points, the curve segment is defined by a cubic polynomial. At each control point, the polynomial changes in such a manner that the 1st and 2nd derivative vectors are the same from either side. The control parameters record must contain vectorAtStart, and vectorAtEnd which are the unit tangent vectors at controlPoint[1] and controlPoint[n] where n = controlPoint.count. Note: only the direction of the vectors is relevant, not their length.</documentation>
  </annotation>
  <complexContent>
    <extension base="gml:AbstractCurveSegmentType">
      <sequence>
        <annotation>
          <documentation>Unlike in gml:CubicSplineType, positions can only be specified in one way: inlined using gml:posList. The number of direct positions in the list must be at least three.</documentation>
        </annotation>
        <element ref="gml:posList"/>
        <element name="vectorAtStart" type="gml:VectorType">
          <annotation>
            <documentation>"vectorAtStart" is the unit tangent vector at the start point of the spline.</documentation>
          </annotation>
        </element>
        <element name="vectorAtEnd" type="gml:VectorType">
          <annotation>
            <documentation>"vectorAtEnd" is the unit tangent vector at the end point of the spline.</documentation>
          </annotation>
        </element>
      </sequence>
      <attribute name="interpolation" type="gml:CurveInterpolationType" fixed="cubicSpline">
        <annotation>
          <documentation>The attribute "interpolation" specifies the curve interpolation mechanism used for this segment. This mechanism uses the control points and control parameters to determine the position of this curve segment. For a CubicSpline the interpolation is fixed as "cubicSpline".</documentation>
        </annotation>
      </attribute>
      <attribute name="degree" type="integer" fixed="3">
        <annotation>
          <documentation>The degree for a cubic spline is "3".</documentation>
        </annotation>
      </attribute>
    </extension>
  </complexContent>
</complexType>

<attribute name="interpolation" type="gml:CurveInterpolationType" fixed="cubicSpline">
  <annotation>
    <documentation>The attribute "interpolation" specifies the curve interpolation mechanism used for this segment. This mechanism uses the control points and control parameters to determine the position of this curve segment. For a CubicSpline the interpolation is fixed as "cubicSpline".</documentation>
  </annotation>
</attribute>

<attribute name="degree" type="integer" fixed="3">
  <annotation>
    <documentation>The degree for a cubic spline is "3".</documentation>
  </annotation>
</attribute>