Augmented reality instructions for construction toys enabled by accurate model registration and realistic object/hand occlusions

BRICKxAR is a novel augmented reality (AR) instruction method for construction toys such as LEGO®. With BRICKxAR, physical LEGO construction is guided by virtual bricks. Compared with the state of the art, accuracy of the virtual–physical model alignment is significantly improved through a new design of marker-based registration, which can achieve an average error less than 1 mm throughout the model. Realistic object occlusion is accomplished to reveal the true spatial relationship between physical and virtual bricks. LEGO players’ hand detection and occlusion are realized to visualize the correct spatial relationship between real hands and virtual bricks, and allow virtual bricks to be “grasped” by real hands. The major finding of the research is that the integration of these features makes AR instructions possible for small parts assembly, validated through a working AR prototype for constructing LEGO Arc de Triomphe and quantitative measures of the accuracies of registration and occlusions. In addition, a heuristic evaluation of BRICKxAR’s features has led to findings that the present method could advance AR instructions in terms of enhancing part visibility, match between mental models and visualization, alignment of physical and virtual parts in perspective views and spatial transformations, tangible user interface, consolidated structural diagrams, virtual cutaway views, among other benefits for guiding construction.