A shape factor to characterize the quality of spheroids.

A shape factor eR has been devised to describe how the form of spherical particles approaches that of a true spheroid, based on a two-dimensional image analysis. Both the deviation of shape from a circle towards an ellipse and surface irregularities influence the value of eR. Using a set of model figures such as squares, triangles, diamonds and stars, it could be shown that eR clearly differentiates between different polygonally symmetric figures, even in the case where common shape descriptors such as the aspect ratio provide equal values. The value of eR is 1.0 in the case of a perfect spheroid, while ellipticity and surface roughness lead to a significant change in the value.