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Archaeological Photogrammetry

 

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CAST researchers at Ostia Antica; laser scanning, photogrammetry, university of arkansas

Archaeological Photogrammetry at CAST

The Center is involved in a several forms of photogrammetric research, many of which are directly related to the field of archaeology. Over 10 years ago, the Center was developing methods for easily and inexpensively extracting three-dimensional measurements from 35mm stereo photographs using close-range softcopy photogrammetry. More recent projects include a multi-year research project in Tiwanaku, Bolivia. This work included the photogrammetric processing of historic photographs collected decades ago by the Bolivian military, from which topographic models and orthophotos were produced and integrated with other remotely sensed data to form a comprehensive three-dimensional model of the ancient city. In the spring of 2007, CAST crossed the Atlantic to collect close-range digital images of the ancient harbor city of Rome, Ostia Antica, to be used in a two semester honors colloquium at the University of Arkansas, "Visualizing the Roman City." These terrestrial-based photogrammetric quality photographs were used by students to produce three-dimensional reconstructions of several structures at Ostia. CAST has most recently began work on providing the archaeological community with CORONA imagery-based achaeological atlas of the Near East, North Africa, and parts of central Asia. Field programs involving archaeological photogrammetry can be found here. Click here for information on other ways CAST uses photogrammetry. 

What is Photogrammetry?

Photogrammetry falls under the broader category of Geomatics, and, according the American Society for Photogrammetry and Remote Sensing, can be 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.