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 1941 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 37.8, 37.8 and 20.1. The Maximum ground residuals for E, N and Elev. are 146.7, 278.5 and 73.0.
Do You Graphics (Woodbine, MD) supplied the scanned images of 202 photos from the National Archives in College Park, MD. The aerial photography was flown at 1"=1667' negative scale in 1941. Flying was completed on 11/27/1941 for this Department of Agriculture project. Image quality was compromised by dirt and scratches. The "desk top" scanner used to scan the photos was not of modern Photogrammetric quality. There was no camera calibration supplied for these images. A focal length of 152.00 mm was assumed. A selected point on each fiducial was measured on all of the images. It was found that the minimum and maximum distances between the side fiducials differed by more than 2 mm. A set of fiducial coordinates were selected and used to make a camera calibration file with a maximum geometry for input into the ISAT program. 439 ground control points were used.
The RMS of the ground control E, N and Elev. are 37.8, 37.8 and 20.1.
The Maximum ground residuals for E, N and Elev. are 146.7, 278.5 and 73.0.
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 1941 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.