Blob Analyzer Intrinsic Inertia Results The intrinsic moments of inertia measure the inertial resistance of the blob to rotation about its principal axes. Because their orientation depends on the coordinate system in which the blob is represented, the principal axes, major and minor, are defined in the section on extrinsic blob properties. Intrinsic Inertia Results ACEUser's Guide, 3.6.x, 18316-000 Rev A Page 420 Object Definition Roundness The degree of similarity between the blob and a circle. Values are between 0 and 1, where 1 is a perfectly circular blob.
Convex Perimeter Calculated from the average projected diameter of the blob and is more stable and accurate than the raw perimeter for convex shapes, including rect- angular forms. Convex perimeter is calculated using an approx- imation of Crofton's theorem. The blob's diameter is determined by projections made at four dif- ferent orientations: 0, 45, 90 and 135 degrees. The average diameter calculated from these pro- jections is multiplied by PI to obtain the convex perimeter. Raw Perimeter The sum of the pixel edge lengths on the contour of the blob. Because the raw perimeter is sensitive to the orientation of the blob with respect to the pixel grid, results may vary greatly.
Unless blobs are non-convex, convex perimeter results provide greater accuracy.