JVRB, 14(2017), no. 2.: Physical models have always been used in the field of molecular science as an understandable representation of complex molecules, particularly in chemistry. Even if physical models were recently completed by numerical in silico molecular visualizations which offer a wide range of molecular representations and rendering features, they are still involved in research work and teaching, because they are more suitable than virtual objects for manipulating and building molecular structures. In this paper, we present a markerless tracking method to construct a molecular virtual representation from a flexible and modular physical model. Our approach is based on a single RGB camera to reconstruct the physical model in interactive time in order to use it as a tangible interface, and thus benefits from both physical and virtual representations. This method was designed to require only a light virtual and augmented reality hardware setup, such as a smartphone or HMD & mounted camera, providing a markerless molecular tangible interface suitable for a classroom context or a classical biochemistry researcher desktop. The approach proposes a fast image processing algorithm based on color blob detection to extract 2D atom positions of a user-defined conformation in each frame of a video. A tracking algorithm recovers a set of 2D projected atom positions as an input of the 3D reconstruction stage, based on a Structure From Motion method. We tuned this method to robustly process a few key feature points and combine them within a global point cloud. Biological knowledge drives the final reconstruction, filling missing atoms to obtain the desired molecular conformation.
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