<complexType name="OffsetCurveType">
    <annotation>
        <documentation>An offset curve is a curve at a constant
		 distance from the basis curve. They can be useful as a cheap
		 and simple alternative to constructing curves that are offsets	
		 by definition.</documentation>
    </annotation>
    <complexContent>
        <extension base="gml:AbstractCurveSegmentType">
            <sequence>
                <element name="offsetBase" type="gml:CurvePropertyType">
                    <annotation>
                        <documentation>offsetBase is a reference to thecurve from which this
							 curve is define	as an offset.</documentation>
                    </annotation>
                </element>
                <element name="distance" type="gml:LengthType">
                    <annotation>
                        <documentation>distance is the distance at which the
							 offset curve is generated from the basis curve. In 2D systems, positive distances
							 are to be to the left of the basis curve, and the negative distances are to be to the 
							 right of the basis curve.</documentation>
                    </annotation>
                </element>
                <element name="refDirection" type="gml:VectorType" minOccurs="0">
                    <annotation>
                        <documentation>refDistance is used to define the vector
       direction of the offset curve from the basis curve. It can
       be omitted in the 2D case, where the distance can be 
       positive or negative. In that case, distance defines left
       side (positive distance) or right side (negative distance)
       with respect to the tangent to the basis curve.

       In 3D the basis curve shall have a well defined tangent 
       direction for every point. The offset curve at any point 
       in 3D, the basis curve shall have a well-defined tangent
       direction for every point. The offset curve at any point
       (parameter) on the basis curve c is in the direction
       -   -   -         -               
       s = v x t  where  v = c.refDirection()  
       and
       -
       t = c.tangent()
                                                    -
       For the offset direction to be well-defined, v shall not
       on any point of the curve be in the same, or opposite, 
       direction as
       - 
       t.

       The default value of the refDirection shall be the local
       co-ordinate axis vector for elevation, which indicates up for
       the curve in a geographic sense.

       NOTE! If the refDirection is the positive tangent to the
       local elevation axis ("points upward"), then the offset
       vector points to the left of the curve when viewed from
       above.</documentation>
                    </annotation>
                </element>
            </sequence>
        </extension>
    </complexContent>
</complexType>

• gml:AbstractCurveSegmentType
  • OffsetCurveType
  • gml:OffsetCurve