The new era of technological development in the field of GIS and remote sensing, Aerial Photogrammetry, has gathered enormous importance. In short and simple photogrammetry is measuring technique. Aerial photogrammetry is the technique used for measuring 2D as well as 3D objects from photographs and also from imagery captured by tape, disc, video, CCD cameras or taken by radiation sensors.
Types of Aerial Photogrammetry : There are mainly two types of Aerial Photogrammetry.
- Analytical Photogrammetry: a stereo pair of analog films are observed and interpreted manually under a stereo plotter/stereoscopic vision.
- Digital Photogrammetry: It is very expensive and the only automated mapping technique, where aerial films are converted into digital image data, with the help of high resolution. it is very useful for the creation of 3D models like DEM etc.
Techniques of Aerial Photogrammetry:
On the basis of number of photographs three techniques can be stated though depending on the required result and material availability Aerial photogrammetric techniques may vary.
- Mapping from single photograph : it is useful for describing plane two-dimensional objects. it is again divided into –
- paper strip method
- optical rectification
- numerical rectification
- mono plotting
- digital rectification.
- Stereo Photogrammetry : here a stereo pair is used under a stereo metric camera. With the help of this stereoscopic vision two photo or images are matched to get a three-dimensional view. Here a common feature or object which is present in both photo are tried to get matched to get a three dimensional view. it has three types namely –
-
- analogue
- analytical
- digital
- Mapping from several photographs : here more than two photographs are used to get a better quality three dimensional information. Photographs of three dimensional objects are taken from several location and from various position for getting a better information of an object.
Amongst all only analytical and digital techniques are used widely for Aerial Photogrammetry purposes which are already discussed earlier.
What can we get from aerial photogrammetry (uses of Aerial Photogrammetry) ?
- Ortho-photo or rectified photographs : here we get the processed image where all distortions are removed. those distortions occur when the images are captured.
- Co-ordinates of any specific object or point : the process begins with registering some ground control points. Then the image or photo become geographically and spatially organized that one can get the ground information about any area from the photo or image.
- Topographical and thematic maps : the use of this starts with school level geography study and extends up to higher level of study including national level secrets and many other usages.
Therefore aerial photogrammetry is a process that collectively includes the ground-rectification with high precision, gathering reliable geographic information about the mapped objects and digital reconstruction of the 3d objects.