Photogrammetry

The practice of determining the geometric features of an object using photographic images is generally referred as Photogrammetry. It was developed in mid-nineteenth century and the practice is as old as photography. To calculate the distance between two points on a plane parallel to photographic image plane ,the distance on the image have to be measured .This is possible only if the scale of image is available. In various fields like topographic mapping, engineering, architecture, manufacturing, quality control, police investigation and geology photogrammetry is used. Archaeologists use this method to produce plans for large sites easily and meteorologists also use photogrammetry to calculate the speed of tornado as the objective weather data regarding the tornado is very difficult to estimate. In movie post production photogrammetry is used to merge live action with computer-generated imageries.

Methods used in photogrammetry

Methods from different disciplines like optics and projective geometry are used in photogrammetry. The 3D co-ordinates in the photogrammetric method help to define the location of object points in the 3D space. The positions of object point’s images on the film or electronic imaging device can be defined with the help of image co-ordinates. The exterior point of reference or orientation of camera helps in defining its position in space .View direction of the points also can be calculated easily. Geometric constraints of the imaging process can be calculated using the inner orientation. It includes focal length of lens and description of distortion of lens. American Society for Photogrammetry and Remote Sensing (ASPRS) defines photogrammetry as an art, science and technology to obtain trustworthy information about physical objects and environment by recording, measuring and interpreting photographic patterns and image.

Integration

Photogrammetric data is very exact in the x and y direction and dense range data is more accurate in z direction Techniques like LiDAR, laser scanners, white –light digitizers are used to supply this kind of range data. With the help of georeferencing aerial photos and LiDAR a 3D visualization can be created. Same reference frame has to be used to rectify the aerial photos and then drape the rectified image on the top of the LiDAR grid. Using aerial photographs or satellites it is not a difficult task to create a digital terrain models.

Applications of Photogrammetry

Photogrammetry is used in collision engineering, mainly with automobiles. In case of accidents photogrammetry is used to find the rate of deformation occurred in the car and the amount of energy needed for that deformation. The amount of energy can be used to find out information about the accident.

Questions:

• Define photogrammetry?
• What are the various methods used  in photogrammetry?