A system and methods for attaining optimal precision digital image stereoscopic direction and ranging through air and across a refractive boundary separating air from a liquid or plasma using stereo-cameras, and employing a minimum variance sub-pixel registration method for determining precise estimates of the parallax angle between left and right stereo images. The system and methods can also track measurement and estimation variances as they propagate through the system in order to provide a comprehensive precision analysis of all estimated quantities.