Data having some similarities and some dissimilarities may be clustered or grouped according to the similarities and dissimilarities. This structure allows for profiling of the exterior wall of a liner such that one or more continuous channels are provided along the length of the lined tubular system. 03 \u03bb, where CML is an amount of a generated third-order coma aberration per 1 degree of tilt of the objective lens, and CMF is an amount of a generated third-order coma aberration per 1 degree of tilt of off-axis light.