A browser port of the system from the SIGGRAPH Asia 2009 paper by Yotam Gingold, Takeo Igarashi, and Denis Zorin. Place primitives over a guide image and annotate them; the 3D model on the right is built from your input.
Scroll to zoom, drag with the middle button or hold Space to pan. In the 3D view, drag to rotate and scroll to zoom. Select (V), Pan (H), Zoom (Z). Undo: Ctrl/Cmd+Z.