1. A method for 3D imaging of an occupant in a motor vehicle for vehicle occupancy determination, the method comprising: projecting an illumination light source onto a motor vehicle intended to be analyzed for vehicle occupancy determination, said illumination source comprising structured light in the Short Wave Infrared (SWIR) band, said structured light being projected through an optical element comprising a patterned grid, a reflection of said source light being sensed by an imaging sensor; capturing said projected pattern by said imaging sensor; calibrating said captured projected pattern comprising: determining a relationship between actual intensity of said projected pattern and pixel intensity values; fitting said established relationship with a high order polynomial function; calculating an inverse function; and using said inverse function to rectify said pattern; shifting sensed reflected source light of said captured rectified pattern to a wavelength range of a charge-coupled device (CCD), said wavelength-shifted light being an image in a structured pattern; using an infrared detector operating in the near infrared range of 700-1000 nm to detect said wavelength-shifted light; for each pixel in said structured patterned image: analyzing said detected wavelength-shifted light to determine an amount of distortion caused by 3D surface variation at this pixel location; and converting said distortion to a depth value for this pixel; constructing a 3D image using each pixel's respective depth value; and determining a number of occupants in said vehicle by analyzing said 3D image.