Structured Annotations for 2D-to-3D Modeling

We present a system for 3D modeling of free-form surfaces from 2D sketches. Our system frees users to create 2D sketches from arbitrary angles using their preferred tool, which may include pencil and paper. A 3D model is created by placing primitives and annotations on the 2D image. Our primitives are based on commonly used sketching conventions and allow users to maintain a single view of the model. This eliminates the frequent view changes inherent to existing 3D modeling tools, both traditional and sketchbased, and enables users to match input to the 2D guide image. Our annotations-same-lengths and angles, alignment, mirror symmetry, and connection curves-allow the user to communicate higherlevel semantic information; through them our system builds a consistent model even in cases where the original image is inconsistent. We present the results of a user study comparing our approach to a conventional “sketch-rotate-sketch” workflow.