Digital Photogrammetry








Photogrammetry has been defined by the American Society of photogrammetry remote Sensing as the art, science, and Technology of obtaining reliable information about physical objects and the environment through processes of recording, measuring, and interpreting photographic images and patterns of recorded radiant electromagnetic energy other phenomena.
As implied by its name, the science originally consisted of analysing photographs, however the use of film cameras as greatly diminished in favour of digital sensors. Photogrammetry has expanded to include analysis of other records, such as digital imagery, radiated acoustical energy patterns, laser ranging measurements, and magnetic phenomena.
Photogrammetry is the science, technology and art of making precise measurements on photographic or other imagery to derive reliable topographic information (two or three dimensional coordinates) for a set of points.

According to the definition digital photogrammetry are of two distant areas:
1. Metric photogrammetry
2. Interpretative photogrammetry

  • Metric Photogrammetry

It consists of making precise measurements from photos and other information sources to determine, in general, the relative locations of points. This enables finding distances, angles, areas, volumes, elevations, and sizes & shapes of objects.
The most common applications of metric photogrammetry are the preparation of planimetric and topographic maps from photographs, and the production of orthophotos from digital imagery. The photographs are most often aerial (taken from an airborne vehicle), but terrestrial photos (taken from earth based cameras) and satellite imagery are also used.

  • Interpretative Photogrammetry




Interpretative photogrammetry deals principally in recognising and identifying objects and judging their significance through careful and systematic analysis. It is included in the branches of image interpretation and Remote Sensing.
Image interpretation and remote Sensing include not only the analysis photography but also the use of data gathered from a wide variety of sensing instruments, including multispectral cameras, infrared sensors, thermal scanners, and side looking airborne radar. Remote Sensing instruments, which are often carried in vehicles as a remote as orbiting satellites, are capable of providing quantitative as well as qualitative information about objects.
At present it, set recognition of the importance of preserving our environment it and natural resources, photographic interpretation and Remote Sensing are both being employed extensively as tools in management and planning.

Quantitative Metric photogrammetry may be divided in two interrelated branches which are as follows:-
1. Instrumental Photogrammetry
2. Analytical Photogrammetry



Instrumental Photogrammetry mainly deals with reconstruction of imaging conditions using high precision measuring instruments.






Analytical Photogrammetry deals with deals with mathematical and physical models required to describe the imaging conditions and their utilisation in deriving the required topographic information. To an extent the analytical photogrammetry replicates the function of instrumental photogrammetry through use of high speed computers. It also has certain distinct advantages over instrumental photogrammetry in non-conventional areas such as satellite photogrammetry. 


Although photogrammetry was born for architectural survey, it can be considered the first remote sensing Technology based on the acquisition of object's geometric properties from photographic images. Nowadays it is widely used in in topographic aerial survey and mapping, and for military purposes.