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Photogrammetry

 

CAST Photogrammetry at Tiwanaku Bolivia, Adam Barnes, Jack Cothren, historic aerial photographs, research, university of arkansas

Photogrammetry at CAST

Digital photogrammetry is a major research arena for the Center. The Center has a significant suite of photogrammetric hardware and software, including: Leica Geosystems' LPS, Stereo Analyst, GPro and Orima, MathWorks MatLab, EOS Systems Photomodeler, PCI Geomatics' Geomatica, Trimble GPS equipment, and other resources. CAST draws on both aerial and close-range photogrammetric techniques for various projects, and is constantly investigating new techniques for these methods. Examples of photogrammetric research include topics such as: self organizing image block techniques, integration of terrestrial LiDAR and high-resolution digital images, low cost aerial mapping, photogrammetric processing of historic aerial photography, reconstruction of ancient structures using close-range photogrammetry, and CORONA satellite digital atlas for archaeologist. An early application of photogrammetry at the Center was the development of methods for easily and inexpensively extracting three-dimentional measurements from 35mm stereo photographs using close-range softcopy photogrammetry. See the Archaeological Photogrammetry page for more information on how CAST uses photogrammetry and the Computer Modeling of Archaeological Ruins page for information on how CAST uses photogrammetry in Field Programs.

What is Photogrammetry?

Photogrammetry falls under the broader category of Geomatics, and, according the American Society for Photogrammetry and Remote Sensing, is defined as "the art, science and technology of obtaining reliable information about physical objects and the environment through the process of recording, measuring and interpreting photographic images and patterns of electromagnetic radiant imagery and other phenomena." A simplified definition could be, "extracting three-dimensional measurements from two-dimensional data."

Why Use Photogrammetry?

Photogrammetry allows for the extraction of three-dimensional features from remotely sensed data (close-range, aerial, orbital, etc.). Applying photogrammetric techniques is not a trivial process and the learning curve can be near vertical (no pun intended). In fact, when dealing with aerial photography or satellite imagery, there are alternative methods for geometrically "adjusting" spatial data that are relatively simple (e.g. rubber sheeting). Although these methods do play an important role for GIS users, they do not create a suitable product for making accurate geometric measurements. The photogrammetric process is needed to confront the inevitable systematic and non-systematic errors introduced when an image is captured or made digital (e.g. terrain relief, camera orientation, lens/sensor distortion, and scanner distortion). It is only after solutions are found for these errors that accurate topographic and plainimetric information can be extracted from a digital image.