The ellipsoid is defined in its own coordinate system, centered at the origin, with the semi-axes <radiusX>, <radiusY> and <radiusZ> along the x-, y- and z-axis. <radiusY> and <radiusZ> default to <radiusX>, so that a single radius gives a sphere.
<revolutionAngle> limits the ellipsoid to a sector about the z-axis, starting at the x-axis and turning towards the y-axis; without it the ellipsoid is complete. Unlike the other angles in CPACS, which are given in degrees, <revolutionAngle> is given in radians; it lies between 0, excluded, and 2π.
Figure (a) shows the semi-axes in the coordinate system of the ellipsoid. Figure (b) shows a sector with a revolution angle of 3π/2: it starts at the x-axis and turns about the z-axis towards the y-axis, so that the quarter between the negative y-axis and the positive x-axis is missing. The angle is drawn in a plane parallel to the x-y plane above the ellipsoid, where it is not hidden by the solid.
Where <radiusX> and <radiusY> differ, the angle is the parameter of the ellipse in the x-y plane, not the polar angle of the cut: for a revolution angle α, the end face of the sector lies at the polar angle atan2(radiusY · sin α, radiusX · cos α).
The sector of figure (b) as an element of a library; the revolution angle is given in radians:
<genericElement uID="element_ellipsoidSector">
<name>Ellipsoid sector</name>
<geometry>
<ellipsoids>
<ellipsoid>
<radiusX>0.6</radiusX>
<radiusY>0.4</radiusY>
<radiusZ>0.3</radiusZ>
<revolutionAngle>4.71238898</revolutionAngle>
</ellipsoid>
</ellipsoids>
</geometry>
<mass>
<density>600</density>
</mass>
</genericElement>