1. A method for creating three dimensional lattice structures in computer-aided design models and comprising: receiving a solid model containing a plurality of boundary surfaces for a void region; computing a bounding box of the solid model and a plurality of grid points on an axis-aligned grid within the bounding box; creating a lattice cell layout for a lattice structure within the void region; computing an implicit model defined by a scalar value for each of the grid points on the axis-aligned grid, wherein the scalar value for each grid point is determined by: calculating a surface distance based on a minimum distance for the grid point to the plurality of boundary surfaces; calculating a lattice distance based on the minimum distance for the grid point to the lattice structure; and setting the scalar value based on a lesser of the surface distance and the lattice distance; extracting the lattice structure in the solid model based on the implicit model; and manufacturing the extracted lattice structure.