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General Description
Explanation of the ProcessTechnology Service Corporation provides digital softcopy imagery products from digitized stereo pair aerial photographs. Using a Digital Photogrammetric Workstation (DPW), TSC generates Digital Terrain Model (DTM) data and feature (building, tower, etc.) data that can be used in a variety of software and sensor applications, including conducting image analyses, providing data references including image and topographic maps, and performing geo-positioning.
TSC is currently providing databases showing all structures larger than single family homes within ten nautical miles of selected airports in the United States. The databases are being used in a project for the United States Federal Aviation Administration (FAA) to predict radar performance at locations on or near these airports.
TSC has produced over 64 databases for the FAA, the majority of which are being used for siting the FAA's new airport surveillance radar, the ASR-11. An additional 35 databases are either on order or under production. TSC has also generated a database for the Toronto Airport for the Canadian Government, and a pair of databases for the Naval Air Warfare Center in Maryland.
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TSC receives aerial photographs of an area in a digitized format from an outside source who has flown the required mission and digitized the photographs by scanning the images. For each of our current projects, fifty photographs are used.
The photographers provide TSC with an ALBANY file, which gives the absolute position and orientation of the camera for each photograph that is taken. The knowledge of the camera geometry allows TSC to precisely relate points on the photograph to points on the ground for enhancing the absolute accuracy.
The images and the image support data are next input to the model. An interior orientation is performed that relates the digitized film imagery to its original film coordinates. Rectification is then performed so that the view of the image will effectively be from directly overhead. The rectification allows the distortion and elevation differences on the terrain and orientation of the camera to be removed.
Automatic terrain extraction, which automatically generates a digital terrain matrix file, is next performed. TSC then performs interactive terrain editing, which allows the correction of any errors that result from the automatic terrain extraction process.
Feature extraction is perfomed next. The aerial photographs a three-diminsional veiw of the tops of the buildings. A simplified outline of the top of the building is first collected. The sides of the buildings are added by the process of dropping lines from the corners at the top to the ground. The output of this process is the vertices of a series of plates corresponding to the roof and sides.
Floating structures such as bridges are difficult to collect accurately, due to the difficulty in seeing the sides of such structures in the photographs. For the same reason, buildings with structured sides are also difficult to model accurately.
Upon completion of feature extraction a series of parametric programs are run to check the accuracy of the terrain and feature extraction data. The data points are again reviewed and corrections are made as necessary.
The database product is now complete. The database can be provided in the format and on the medium required by the customers application program.
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