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 sketch-based, 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 higher-level 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.