For simpler scanning in 3D ultrasound imaging, free hand 3D ultrasound imaging is used. Various registration techniques, such as filtering of position signals based on density of scanning and/or counteracting depth deformation due to pressure, may be used for aligning frames relative to each other in 3D space. To deal with curvature of the skin surface resulting in different frames of data representing the same locations, the frames are grouped by orientation. Data representing the same locations in frames of the same or similar orientation are combined. Frame groups of different orientations but of a same sweep of the transducer along the skin are combined into a volume. Volumes from different sweeps are combined. For combining data representing a same location, the values are weighted based on the likelihoods of ultrasound values representing different locations being accurate or correct.
