The GetEllipseParams method of the ICurve interface returns:

The return value is an array of doubles with the following format:

[ centerptX, centerptY, centerptZ, majorRad, majorAxisX, majorAxisY, majorAxisZ,
minorRad, minorAxisX, minorAxisY, minorAxisZ ]

But if the curve is a partial ellipse with a start and end point, how do I know which way the ellipse curve runs from the start to end point.  For arcs the GetCircleParams method returns an "axis" which gives me the "sense" from which I can determine which way the arc runs from the start to the end point.  Is there something similar for the partial ellipse?