In some embodiments, a motion estimation method and engine are provided. When the portable unit is mounted to the docking cart, the docking cart transforms the portable unit into a cart-based system with enhanced features and functionality such as improved ergonomics, ease of use, a larger display format, external communications connectivity, multiple transducer connections, and increased data processing capabilities. The controller coordinates all the image capture functions of the spectral filter. Upon drying the suspension shrinks to provide a mechanically-hard film subsequently usable to provide a sample for spectroscopic analysis. The transmission time of image data and the volume of a memory for storing the image data are also reduced. The coil peak current is adjustable based at least in part on a feedback signal generated in response to a load condition.