An illustration of the procedure underlying the best-fit algorithm. Only those points in each array in the library of 569 point arrays are used as input that overlap with the capsid, here shown as a shaded ring structure. Once the best-fit point array has been selected, its remaining points overlapping with the capsid interior must also be descriptors of capsid geometry. They therefore predict additional structural constraints. In our case studies below we show that these predictions provide additional insights into the genome packaging structure that agree well with experimental data.