Fig. 1

a Overview of building the 2D projection image library from 3D biological shapes. Known structures are resized to have the same particle volume and are aligned with each other to determine their similarity. Representative shapes are picked for each shape type and projection images are simulated based on them for the 2D projection image library. b Overview of finding candidate 3D models from a few 2D experimental images in real space. The input image is aligned against the library of images, and the close matches are mapped to their corresponding 3D models, resulting in a potential 3D candidate model