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Philadelphia County DOQ Data (Digital Orthophoto Quadrangle Data)
Digital Orthophoto Quadrangle Data (DOQ) basics
A digital orthophoto is a digital image of an aerial photograph in which displacements caused by the camera and the terrain have been removed. It combines the image characteristics of a photograph with the geometric qualities of a map. The standard digital orthophoto produced by the USGS is a black-and-white, or color infrared, 1-meter ground resolution quarter quadrangle image. The standard quarter-quadrangle image covers 3.75 minutes of latitude by 3.75 minute of longitude, at a scale of 1:12,000 cast on the Universal Transverse Mercator projection based on the North American Datum of 1983. Each image also has between 50 and 300 meters of overedge to facilitate tonal matching for mosaicking of adjacent images
DOQ FILE TYPES AND NAMING CONVENTIONS
Each image file is compressed using software developed by the Joint Photographic Experts Group (JPEG) using a quality factor of 30. Most image display and image processing programs require that these images be reconstituted (or decompressed) before use.The naming convention for DOQ files follows the data set naming convention used in the USGS National Digital Cartographic Data Base. Here is a brief description of the naming convention.
| t | indicates type of quad (o = Orthophoto) |
|---|---|
| yy | indicates southeast latitude of the one-degree block in which the quad resides |
| xxx | indicates southeast longitude of the one-degree block in which the quad resides |
| zz | is the 7.5-minute section number of the one-degree block in which the quad resides (reading left to right from northwest corner) |
| .dd | indicates the 3.75-minute quarter of the 7.5-minute quadrangle (ne, nw, se, sw) |
| s | indicates file type: header [h], standard DOQ file with header attached [s], compressed DOQ with no header [c], or reconstituted file [r] (from the compressed version) |
| o4309108.ne | A compressed image file, for the northeast 3.75-minute quarter of the eighth 7.5-minute quadrangle of the one-degree block whose southeast corner is 43-degrees north latitude and 91-degrees west longitude. |
|---|
Reconstructed DOQs for Philadelphia County 7.5-minute quadrangles
- These JPEG-format images were produced by merging 15-percent samples of the four quarter-quadrangle DOQ JPEG images, using Corel PhotoPaint. Individual image files run approximately 3.8 megabytes, so be patient and make sure your machine is ready to crash! Images that load partially, leaving a black band across the image bottom, may be restored by reloading after increasing web browser cache sizes.
The Penn Campus
- Penn, from 32nd Street to 40th Street, Ludlow Street to the Bio Pond -- Link broken?
- David Toccafondi, the Van Pelt Reference administrative assistant, used Photoshop 3.0 for Windows to crop and rotate this image. The JPEG-format file is about 500K.
- Other, smaller, images of Penn
- View of Penn campus, 38th Street to 34th Street, Walnut Street to Hamilton Walk
- View of Penn campus, 36th Street to Franklin Field, Walnut Street to Franklin Field
- View of Penn campus, 40th Street to 36th Street, Walnut Street to Hamilton Walk
- These images have been created using IMDISP, a JPL image processing and display package distributed by the U.S. Geological Survey on its "Olmsted County" Project, Minnesota CD-ROM. A more flexible, but seemingly more memory-intensive image processing and display package, IMVIS, distributed on the U.S. Geological Survey CD-ROM, Data, software, and applications for education and research in geology, Virginia (Open File Report 93-231) can also display these images. Each GIF-format image, saved from screen captures, is about 90K.
Other Philadelphia DOQ-derived images
- Logan Circle (3x, I think)
- The Philadelphia Zoo and adjacent Conrail railroad tracks
- View of W. Girard Avenue and 2nd Street, sampled at 2x, in JPEG format
- View of W. Girard Avenue and 2nd Street, sampled at 2x, in GIF format
- View of W. Girard Avenue and 2nd Street, sampled at 1x, in JPEG format
- View of W. Girard Avenue and 2nd Street, sampled at 1x, in GIF format
- Custis Woods, Cheltenham Township (1x)
- Custis Woods, Cheltenham Township (1x) - A GIF image, with contrast boosted using IMDISP's "AUTOENHANCE" feature
- Custis Woods, Cheltenham Township (2x) - Note the quarry
Image display software that appears to handle DOQs
For users who can't afford Photoshop, PhotoPaint, PaintShop Pro, or other commercial image processing and display software, there's still hope!- IMDISP v7.9 - From Watershed boundaries and digital elevation model of Oklahoma derived from 1:100,000-scale digital topographic maps (USGS Open-File Report 95-727)
- IMDISP v7.9 - Alternate FTP access to same site
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