1. A method for determining a three-dimensional model from a plurality of images taken of a geographic region by one or more cameras from different perspectives, comprising: (a) determining, using a first stereo reconstruction technique: (i) a plurality of three-dimensional candidate surface points from the plurality of images, and (ii) which of the images in the plurality of images view each of the plurality of candidate surface points; (b) identifying an empty space between each of the plurality of candidate surface points and each camera model for the respective images determined in (a) to view the candidate surface point; (c) for each of a plurality of pairs of images from the plurality of images, determining, using a second stereo reconstruction technique, a surface estimate for the pair of images, the determining a surface estimate (c) for the pair of images comprising: (i) determining a likelihood of each point in a volume of interest being a surface point based on an empty space identified in (b) such that the likelihood of the point being a surface point is less when the point is inside the empty space than when the point is outside the empty space; and (ii) determining a surface estimate for the pair of images based on the likelihoods determined in (c)(i), wherein a distance between positions of cameras used to generate the pair of images for the second stereo reconstruction technique is less than a distance between positions of cameras used to generate a pair of images used in the first stereo reconstruction technique; and (d) merging the surface estimates determined in (c) to identify a final surface.