1. A computer implemented method for initializing a model, comprising: receiving at least one image of a control object observed in a 3D imaging space; calculating span lengths between opposing sides of the control object; determining a number of span modes of the control object applicable to a frequency distribution of the span lengths; for each span mode, calculating one or more span width parameters from at least part of the distribution of the span lengths; using the span width parameters to initialize at least a portion of a model of the control object; and generating predictive information from an initialized model.