This tile is part of a collection of 1-foot pixel natural color orthophotos covering the 2007 USGS project area contracted by the City of Madison, WI. An orthophoto is remotely sensed image data in which displacement of features in the image caused by terrain relief and sensor orientation have been mathematically removed. Orthophotography combines the image characteristics of a photograph with the geometric qualities of a map. The imagery was captured at 12-bit radiometric resolution and converted to 8-bit radiometric resolution during post processing. The imagery was obtained and processed by all digital means beginning with data acquisition using a Z/I Imaging Digital Mapping Camera (DMC). The orthophotos are available in GeoTIFF and MrSID format, and are tiled/named according to National Map Standards.
The Project will provide updated ortho imagery to existing digital ortho imagery. This project is part of the USGS/National Geospatial-Intelligence Agency (NGA) program to acquire digital ortho imagery for the 133 Urban Areas Program. The USGS footprint for this project includes all of the following USGS 1:24,000-scale topographic quadrangles: Cottage Grove, DeForest, Madison East, Madison West, Middleton, Oregon, Rutland, Stoughton, Sun Prairie, Verona, and Waunakee.
ground condition
Only to be used within context of 2007 Project specifications.
Ayres Associates
After the raw images have been georeferenced and rectified, seamlines between the overlapping photos are created through manual and automated processes. They are placed based upon where they will have the minimum impact on the orthophotography. These seamlines are then visually inspected as part of the QC process to insure that spatial, hue, and contrast variations between photos are minimized and within project specifications.
Project is complete
Orthophotography was generated to meet ASPRS Class 1 for 1"=200' scale mapping.
The aerial photography captured in April of 2007, along with ground control, provided the project with the raw materials needed to create orthophotography meeting the standards laid out for the 2007 City of Madison / USGS Orthophotography project.
Ground control consisted of photo identifiable surveyed points. The imagery was collected using a Z/I Imaging Digital Mapping Camera (DMC). Image quality was verified during the post flight review phase. Factors considered during this review included but were not limited to the presence of smoke and/or cloud cover, contrails, light conditions, snow presence and sun glint. The triangulated strips were rectified with a surface created from a LiDAR mission that took place in 2005, as well as a 2-foot / 4-foot contour surface created in 2000 and 2005. The red, green and blue bands were combined to generate a final orthophoto. The DMC collects twelve bit image data which requires radiometric adjustment for output in standard eight bit image channels. Converting to eight bit results in a reduction of the color range from 4096 to 256 - thus loss of radiometric detail is inevitable. The extra dynamic range of the sensor permits greater object differentiation in shadows and in bright areas. The sixteen bit dynamic range permitted the imagery to be more effectively color balanced than is possible with eight bit imagery. This was accomplished by performing tonal enhancements immediately prior to the reduction from sixteen bit to eight bit data. In addition to color balancing these eight bit images were adjusted to create seamless imagery to the highest extent practically achievable. The imagery was mosaicked using a combination of automated and manual seamlines generation. Project specified tiles were extracted from the mosaic. Final image tiles were reviewed for artifacts and anomalies and adjusted as part of quality control procedures. Adjacent images are compared for consistency in overlap regions. The images are reviewed for rectification problems such as bridge displacements caused by the underlying digital elevation model. When necessary, local corrections to the imagery were performed to minimize such effects.
1802 Pankratz Street