 |
CCH GIS Data Dictionary |
NGA 1 Ft Imagery (Oahu) - This true color ortho-imagery is from National Geospatial-Intelligence Agency (NGA) and the US Geological Survey (USGS). |
|
| Coverage Notes References Downloads |
|||||
ATTRIBUTES: Image ground pixel resolution is 1 foot To view image dates follow this link and hover your cursor over a grid cell or use this procedure. |
|||||
|
NOTES: An orthoimage is remotely sensed image data in which displacement of features in the image caused by terrain relief and sensor orientation have been mathematically removed. ...from the original metadata... Purpose: These data have been created as a result of the need for having geospatial data immediately available and easily accessible in order to enhance the capability of Federal, State, and local emergency responders, as well as plan for homeland security efforts. Compliance with the accuracy standard was ensured by the placement of photo identifiable ground control points and the collection of airborne GPS data.   3) Once this page draws, click 'Query' and check the button next to NGA Quad Index. 4) Click on the map to return the date. (Use the 'back' button to return to the map.)  Hardware/Software used: Source photography - Zeiss RMK TOP15 Cameras, natural color stable base. Control - airborne GPS supplemented with photo identifiable field control. Scanning - Z/I Imaging PhotoScan flatbed metric scanner. Aerotriangulation - Photo-T. Elevation Model - Autocorrelation and manual collection. Radiometric Balancing - Proprietary and COTS Software (PhotoShop). Orthorectification - Z/I Ortho Pro 4.0 software package. Mosaic - OrthoVista software package. Processed on Windows NT/2000 systems. Process used to create the dataset (from the original metadata): The ground control and airborne GPS data was integrated into a rigid network through the completion of a fully analytical aerotriangulation adjustment. The original aerial film was scanned at a resolution of 21 microns. The scans were produced using Z/I Imaging PhotoScan flatbed metric scanners. The scanned images were then used as input, along with ground control, airborne GPS data and camera calibration data into a Z/I Imaging softcopy system for final adjustment. The digital orthophotography was produced in natural color with a 0.3 meter pixel resolution. A step-by-step breakdown of the digital orthophoto production process follows. 1. A representative number of raster image files were visually checked for image quality on the workstation. 2. The digital image files were oriented on the digital orthophoto production workstation. The following information was then loaded onto the workstation. - The camera calibration parameters and flight line direction. - Ground control and pass point locations. - The exterior orientation parameters from the aerotriangulation process. - ASCII file containing the corner coordinates of the orthophotos. - The digital elevation model in a DGN format. - Project-specific requirements such as final sheet size and resolution. - Orientation parameters developed from the aerotriangulation solution. 3. A coordinate transformation based on the camera calibration fiducial coordinates was then undertaken. This transformation allowed the conversion of every measured element of the plates to a sample/line location. Each pixel in an image was then referenced by sample and line (its horizontal and vertical position) and matched to project control. The newly rectified image was visually checked for pixel drop-out and/or other artifacts that may degrade the final orthophoto image. 4. DTM data was imported and written to the correct subdirectory on disk. The final digital orthophotos were referenced to UTM Zone 4, NAD83, meters. 5. The DTM file was reinspected for missing or erroneous data points. 6. A complete differential rectification was carried out using an exponential algorithm that removed image displacement due to topographic relief, tip and tilt of the aircraft at the moment of exposure, and radial distortion within the camera. Each final orthophoto was produced at a 0.3 meter pixel resolution. 7. Each digital orthophoto image was visually checked for accuracy on the workstation screen. The digital orthophotos were then edge-matched using a module of the Ortho Pro software package. 8. Once the orthophotos were inspected and approved for accuracy, the files were copied to the network and downloaded by the orthophoto finishing department. This production unit was responsible for radiometrically correcting the orthophotos prior to completing the mosaicking and clipping of the final tiles. The final 1500-meter X 1500-meter tiles are clipped out and the imagery is output in GeoTIFF format. GeoTIFF files will include the following GeoTIFF tags and keys - - Model Tiepoint Tag - Model Pixel Scale Tag - GT Model Type Geo Key - GT Raster Type Geo Key - Projected CST Type Geo Key - PCS Citation Geo Key - Proj Linear Units Geo Key 9. The processed images were mosaicked using the OrthoVista software. File names were assigned based on the southwest corner of each tile and on the National UTM Grid. 10. The finishing department performed final visual checks for orthophoto image quality. The images were inspected using Adobe Photoshop, which enabled the technician to remove dust and lint from the image files interactively. 11. The final orthophoto images were written out into Arc/Info readable, GeoTIFF format. |
|||||
COVERAGE: .png) NGA 1 Ft Imagery Download Tiff Images from the USGS Data Clearninghouse Download or view MrSid Files Download MrSid, world file and metadata zip package |
|||||
| HoLIS GIS Services | |||||