Photogrammetry is the science and technology of obtaining spatial measurements and other geometrically reliable derived products from photographs. Basic geometric principles applying both traditional analogue and modern digital procedures are related to the central projection of the image in case of typical cameras and to the dynamic projection mostly in case of push-broom sensors, popular in the satellite photogrammetry. The fundamental principle used by photogrammetry is called triangulation. By taking photographs from at least two different locations, so-called “lines of sight” can be developed from each camera to points in a block on the object. These lines of sight (called rays) are mathematically intersected to produce the 3-dimensional coordinates of the points of interest.
Within data processing the most important parts of photogrammetric workflow are: (1) image orientation, (2) model reconstruction, and (3) orthorectification. Image orientation is based mostly on aerial triangulation, however recently the computer vision algorithm, called structure from motion, became more popular in particularly in close range photogrammetry. Both orientation approaches include detection or measurement of the points between overlapping images in a block, control points measurements in a field defining orientation in reference system and check points verifying the orientation process. The satellite photogrammetry due to different projection and much bigger areas of imaging is usually related to Rational Polynomial Coefficients (RPCs) defining preliminary scene orientation during image orientation. However, to receive more accurate results also here the control points measured in a field are in use. The second part of the modern photogrammetric processing is 3D model reconstruction. In past, vectorization within the stereoscopic measurements was the most popular way of using photogrammetric data after the image orientation. The development of the informatics contributed to the development of the image matching algorithms that can provide dense image point clouds, which can be used to the 3D detailed modelling including digital elevation model production. The final step of photogrammetric processing is orthorectification, which delivers cartometric image called orthophoto mosaiced into orthophotomaps. This process comprises the influence of digital terrain model, model of camera (interior orientation) and image orientation (exterior orientation). Orthophotomap and elevation models derived from photogrammetric processing are applied as very popular data source in many GIS systems. The other photogrammetric outcomes are, for example a 3D measurement or 3D models of some real-world object or scene.