(a) A sphere is fitted to a series of transmission images of a zebrafish embryo. The coordinates of the centre (x0, y0, z0) and the radius (R) are determined. A shell of 140 μm thickness around the sphere surface (blue shaded region) will contribute to the projection. (b) The surface of the sphere is divided into vertices (inset). A ray is cast from the sphere centre to each vertex, and the maximum intensity along each ray within the shell is recorded. (c) The resulting spherical maximum intensity projection is then unwrapped to obtain a 2D map of the spherical data (Supplementary Movie 2). Different colours indicate the parts of the embryo that were recorded by the two cameras from two different angles (compare Fig. 1). (d) All endodermal cells spread around the entire embryo are visible in a single image (Supplementary Movie 3). (e) Spatial orientation of the embryo in 3D and on the final map projection. A, anterior; P, posterior; V, ventral; DFC, dorsal forerunner cells.