This dataset was developed through a contract with Aero-Metric Inc, Sheboygan, WI.
Washington County partnered with Ozaukee County on a joint vendor selection process. The selected vendor was contracted to complete similar projects in both Counties. Some cost savings were realized through the two-county project because images straddling the county line were only processed one time and other economies of scale.
1) Roads should at least touch to some degree where the mosaic splice lines stitch adjacent images together. 2) Where reconstruction has not occurred, roads on the 1970 image should touch to some degree the same road on the 2005 orthophotograph. 3) Visual distortion in the resulting image should be minimized.
Every attempt was made to provide orthos that conform to these standards although there may be instances where it was not possible to satisfy all three criteria.
As reported from the aerotriangulation: The RMS of the ground control E, N and Elev. are 5.83, 5.16 and 0.42. The Maximum ground residuals for E, N and Elev. are 16.9, 15.8 and 2.25
SEWRPC supplied the 181 negatives. The aerial photography was flown at 1"=1667' negative scale in 1970. The negatives were cut from the roll and stored individually in sleeves. They were in poor condition. Image quality was compromised by dirt, scratches, and a few creases. Two cameras were used. Their focal lengths were calibrated at 152.64mm and 152.57mm. USGS Camera Calibration Reports from this era, and before, do not have calibrated coordinates for the fiducials. A selected point on each fiducial was measured on many of the images and a set of fiducial coordinates were selected and used to make a camera file with a "best fit" geometry. This was needed for input into the ISAT program. Aero-Metric scanned the negatives using a Zeiss/Intergraph Imaging PhotoScan 2001. 121 ground control points were used.
The RMS of the ground control E, N and Elev. are 5.83, 5.16 and 0.42.
The Maximum ground residuals for E, N and Elev. are 16.9, 15.8 and 2.25
The aerotriangulation, B/W scans and 2005 SEWRPC DEM data were imported into Intergraph's OrthoPro to create rectified images referenced to the State Plane Coordinate System, NAD27 WI South in survey feet. These images were then dodged to even the tone of each image. The mosaic seamlines were auto-generated in OrthoPro and based on each exposure center. Then they were reviewed and edited in some areas to reduce mismatches. Finally, the dodged images and seamlines were used to mosaic, balance and cut the final tiles out. The final tiles were QC'd for void areas and burned to DVD for delivery.
The dataset was delivered as a series of GeoTIFF (Tagged Image File Format) files, each covering a 10,000 by 10,000 foot area or "tile" on the Wisconsin State Plane Coordinate System, South Zone. Each B/W tile is approximately 95 MB in size. The pixel resolution of the images is twelve inches on the ground, with no overlap between adjacent tiles. Each image file includes an accompanying "world" file (".tfw" file extension) containing the coordinate information used to display and register the image in ESRI software.
A single countywide MrSID (Muti-Resolution Seamless Image Database) formatted file was prepared from the GeoTIFF files. The MrSID file is approximately 734 MB in size.
The countywide MrSID file is the format used to distribute the Washington County 1970 Historic Digital Imagery. Contact the GIS Division for additional information and pricing if the GeoTIFF formatted files are required.
This information is subject to errors and omission and is not certified by Washington County.