GM_CurveInterpolation is a list of codes that may be used to identify the interpolation mechanisms specified by an application schema. As a code list, there is no intention of limiting the potential values of GM_CurveInterpolation. Subtypes of GM_CurveSegment can be spawned directly through subclassing, or indirectly by specifying an interpolation method and an associated controlParameters record to support it. Valid meanings for "interpolation" include, but are not limited, to the following:<br/>a) Linear (linear) - the interpolation mechanism shall return DirectPositions on a straight line between each consecutive pair of controlPoints.<br/>b) Geodesic (geodesic) - the interpolation mechanism shall return DirectPositions on a geodesic curve between each consecutive pair of controlPoints. A geodesic curve is a curve of shortest length. The geodesic shall be determined in the coordinate reference system of the GM_Curve in which the GM_CurveSegment is used.<br/>c) Circular arc by 3 points (circularArc3Points) - for each set of three consecutive controlPoints, the middle one being an even offset from the beginning of the sequence of control points, the interpolation mechanism shall return DirectPositions on a circular arc passing from the first point through the middle point to the third point. The sequence of control points shall have an odd number of elements. Note: if the 3 points are co-linear, the circular arc becomes a straight line. <br/>d) Circular arc by 2 points and bulge factor (circularArc2PointWithBulge) - for each consecutive pair of controlPoints, the interpolation mechanism shall return DirectPositions on a circular arc passing from the first controlPoint to the second controlPoint, such that the associated control parameter determines the offset of the center of the arc from the center point of the chord, positive for leftward and negative for rightward. This form shall only be used in 2 dimensions because of the restricted nature of the definition technique.<br/>e) Elliptical arc (elliptical) - for each set of four consecutive controlPoints, the interpolation mechanism shall return DirectPositions on an elliptical arc passing from the first controlPoint through the middle controlPoints in order to the fourth controlPoint. Note: if the 4 controlPoints are co-linear, the arc becomes a straight line. If the 4 controlPoints are on the same circle, the arc becomes a circular one.<br/>f) Clothoid (clothoid) - uses a Cornu's spiral or clothoid interpolation.<br/>g) Conic arc (conic) - same as elliptical arc but using 5 consecutive controlPoints to determine a conic section.<br/>h) Polynomial Spline (polynomialSpline) - the controlPoints are ordered as in a line-string, but they are spanned by a polynomial spline function. Normally, the degree of continuity is determined by the degree of the polynomials chosen. <br/>i) Cubic spline (cubicSpline) - the control points are interpolated using initial tangents and cubic polynomials, a form of degree 3 polynomial spline.<br/>j) Rational Spline (rationalSpline) - the controlPoints are ordered as in a line string, but they are spanned by a rational (quotient of polynomials) spline function. Normally, the degree of continuity is determined by the degree of the polynomials chosen. <br/>This list shall be implemented by a code list, and may vary in actual values from the above strings.<br/>GM_CurveInterpolation::<br/>linear  <br/>geodesic  <br/>circularArc3Points  <br/>circularArc2PointWithBulge  <br/>elliptical  <br/>clothoid <br/>conic  <br/>polynomialSpline  <br/>cubicSpline<br/>rationalSpline<br/>