The Aerial photography, a technique of capture photographing to the Earth’s surface. Aerial photography is the taking of photographs helps to an aircraft, helicopters, balloons, blimps, dirigibles, rockets, parachutes, etc. In recent times use ‘Drone’ to capture Aerial Photographs.
In Photographs the locations of which determined by ground-surveying techniques this technique known as photogrammetry. However, it involves each simultaneous projection of overlapping views. Makes possible the preparation of contour maps or three-dimensional models of the terrestrial surface that has been photographed. Valuable data on Topography, Geology, Hydrology, Soil and Vegetation, Ocean currents, and resources have become accessible with this use of satellite technology and expert interpretation.
Download Aerial Imagery
Downloading Aerial Imagery using USGS Earth Explorer.
2. Select Data Sets, expand Aerial Imagery, and choose your data.
3. Now Download Data.
OpenAerialMap (OAM) is a set of tools for searching, sharing, and using openly licensed aerial imagery.
1. Open OAM online portal.
2. Click anyware on map screne, and show the result on left side.
3. Select your data, and click download button.
Concept of Photogrammetry
Photogrammetry is the Art, Science, and Technology of obtaining probable information about physical objects and the Environment. Through the process of recording, measuring, and interpreting photographic images and patterns of Electomangetic Radiant energy and other phenomena.
Digital photogrammetry is photogrammetry as applied to digital images that are stored and processed on a computer. Digital images can be scanned from photographs or can be directly captured by digital cameras. Many photogrammetric tasks can be automated in digital photogrammetry. Digital. The output products are in digital form, such as digital maps, DEMs, and digital orthophotos saved on computer storage media. With the development of digital photogrammetry, photogrammetric techniques are more closely integrated into Remote Sensing and GIS.
Process of Photogrammetry
Geometry of Aerial Photography
A photographic image is a central perspective. Here implies that every light ray, which reaches the film surface during exposure, passed through the camera lens. Photography implies the position of all the points is controlled by one single point of the image, which controls the Geometry of the entire photographs.
Principal point (PP)- in the point on the image where the optical axis intersects the image plane. The Optical axis an imaginary line that passes through the optical center of the lens and perpendicular to the film or image plane.
The Distance between the perspective center and principal point determines the Focal length.
Seale of Photography
The Scale(S) of the Aerial photograph can be computed either by considering the ratio of the flying height(H) above the ground and the focal length(f) or by the ratio of a known distance in the photograph(ab) and the distance on the ground(AB).
Scale(S) = f/H or ab/AB