Thus, efficient techniques for compressing the description of a geometric model are required. We addressed the compression of the topological component. Compression techniques can be divided into direct techniques, which compress a single-resolution model, and progressive techniques, which encode increasing levels of resolution and naturally support progressive loading transmission. In applications, models of spatial objects need to be build from different data sources and thus need different techniques. Scattered points and lines on a projection plane Data consist of points and lines lying on the surface to be reconstructed, and a projection of them on a plane is given.
Examples are terrain reconstruction, and reconstruction of a surface given a range image of it.
A triangle mesh representing the surface is obtained by first building a plane triangulation including the given points and lines, and then back-projecting such triangulation in 3D space. Three-dimensional scanners provide a cloud of points lying on the surface of an object. The object shape is modeled as a tetrahedralization with vertices at the given points such that all points lie on its boundary. Generation of a multiresolution model Iterative algorithms which build a geometric model by adding few data items at a time to an initial model, thus increasing its resolution and size, provide a mean to build a model at a single resolution, as well as a multiresolution model which captures the intermediate levels of detail between the initial and the final stage of the process. When a high resolution model is given, a symmetrical approach, which progressively deletes data items, thus reducing resolution can be used for the same purpose.