thetaStart — specify vertical starting angle. Default is 0.<br/>
thetaLength — specify vertical sweep angle size. Default is Math.PI.<br/>
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The geometry is created by sweeping and calculating vertexes around the Y axis (horizontal sweep) and the Z axis (vertical sweep). Thus, incomplete spheres (akin to <em>'sphere slices'</em>) can be created through the use of different values of phiStart, phiLength, thetaStart and thetaLength, in order to define the points in which we start (or end) calculating those vertices.