The definition of an arc requires a choice of the type of curve and and in some cases additional points as specified below. (Note that the surface on which the arc is residing is assumed to be either planar or the earth's ellipsoid, as specified in spatialReferencing; if this is not specified, it is assumed to be planar.)
line: no parameters.
nonLinear: the arc is considered as non-linear, but the kind of non-linear curve either is not known or does not match one of the options listed below. supportingPoints is not used.
circularArc: supportingPoints contains only one point, the centre of the circle.
ellipticalArc: supportingPoints contains three points:
(i) the centre of the ellipse, (ii) one of the points where the major axis intersects the ellipse, and (iii) one of the points where the minor axis intersects the ellipse.
(Note that in Arc only two points may be used in the list of points defining position if the arc is a circular or elliptical arc. The points are given in a clockwise direction. Also, if a complete circle or ellipse is intended, the same point is given twice.)
uniformBspline: supportingPoints is not used.
piecewiseBezier: supportingPoints is not used.