1. A system, comprising a processor and a memory in communication with the processor, the memory storing programming instructions executable by the processor to: accept input of a two-dimensional image of a 3-D object that is symmetric about a plane, the 3-D object having a surface; accept input of three pairs of points, each pair being visible in the image, on the surface of the object, and symmetric about the plane; these three pairs of points are not all coplanar in the 3D model; create a model of the object by reconstructing coordinates in 3-space for each point in the three pairs of points in terms of exactly one free parameter; determining coordinates in 3-space of at least one additional pair of symmetric points on the surface of the object, wherein each additional pair includes at least one point that is visible in the image, and each additional pair is specified in terms of the free parameter; and selecting a value for the free parameter that at least approximately maximizes a compactness metric as applied to the reconstructed object in 3-space; and provide output that encodes the model.