  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 1mm 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 integration of these features makes
AR instructions possible for small-parts assembly, validated through a working
AR prototype for constructing LEGO Arc de Triomphe, quantitative measures of
the accuracies of registration and occlusions, and heuristic evaluation of AR
instruction features.
