Abstract: FORMS is a structured light vision system designed to perform accurate, reproducible, fast and not-invasive measurements of human foot shapes and to reconstruct three-dimensional foot models. This work, which is subdivided into two parts, analyzes FORMS modeling, design, calibration and the experimental prototype. Part I, introduces FORMS, defines its kinematic and optical model and describes the data structure developed to speed up image acquisition and processing. The optical model of the system takes into consideration both the radial distortion and the horizontal scale factor of the camera. The system prototype is analyzed and its technical data are outlined.