LADWP Ortho | Tetra Tech R&D

Eastern Sierra Scanning & Orthorectification Project — Los Angeles Department of Water & Power

Tetra Tech was the prime contractor for Los Angeles Department of Water & Power, Eastern Sierra Environmental and Water Rights Group within the Water Operations Division. The Eastern Sierra Scanning Project includes inventory, scanning, rectification and image processing of approximately 9700 historical and contemporary aerial images from the LADWP archives (1929-1996). The images were stored in a variety of analog formats (roll film, 9x9 contact prints, diapositives, etc.) and without an efficient means for indexing, accessing, and viewing the data. Tetra Tech obtained the analog images, inspected and inventoried each image and created a geodatabase that included associated metadata such as flight line, exposure number, orientation parameters, geographic name, image scale, camera calibration data, condition of the film, etc.

To generate orthophotos from the photography Tetra Tech identified 49 separate blocks of coverage for analytical aerotriangulation. Estimates for the location of each exposure were made by locating the first and last exposures of a flight line and interpolating between them. Some of the older sets of photography did not conform to modern standards of photogrammetric design and the location of each exposure was estimated by inspection. Control for aerotriangulation was derived from a combination of materials provided for the purpose by the Department and using supplementary materials available from the USGS. In the course of the project, some of the blocks of photography were found to be deficient in endlap or sidelap requiring that additional control points be identified and introduced to shore up weak areas in the block. Once controlled the photography was orthorectified using the output from the aerotriangulation and a customized terrain surface. The resulting orthos were mosaicked into tiles based on USGS 7.5 minute quadrangles and checked for consistency and continuity. The final delivery to LADWP is a multi-epoch orthorectified GIS base map to support change detection and environmental stewardship of the Owen’s Valley.


Peter Ashley

(925) 280-7441