1. A non-transitory computer readable medium embodying instructions executable by a processor to perform a method for sparse volume segmentation for 3D scan of a target, the method comprising: receiving an observation volume; providing volume data comprising the target; selecting a plurality of key contours of the volume data; building a 3D sparse model of the volume data given the plurality of key contours; determining a volumetric segmentation of a volume data by optimizing an image-based cost function with respect to simultaneously both the set of key contours in a reference space and a transformation which relates a reconstructed model to the observation volume; and outputting a representation of the volume data based on the segmentation using the 3D sparse model.