3D Geographical Information Systems need 3D representations of objects and, hence, 3D data acquisition and reconstructions
methods. Developments in these two areas, however, are not compatible. While numerous operational sensors for 3D data acquisition
are readily available on the market (optical, laser scanning, radar, thermal, acoustic, etc.), 3D reconstruction software
offers predominantly manual and semi-automatic tools (e.g. Cyclone, Leica Photogrammetry Suite, PhotoModeler or Sketch-up).
The ultimate 3D reconstruction algorithm is still a challenge and a subject of intensive research. Many 3D reconstruction
approaches have been investigated, and they can be classified into two large groups, optical image-based and point cloud-based,
with respect to the sensor used, which can be mount on different platforms.