| 1' Panchromatic (B & W) Digital Orthophotography of Loudoun County, VA (Spring 2007) | |
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Data format: SDE Raster Dataset File or table name: GISRSTR.GRSTR.B_W_2007 Coordinate system: Lambert Conformal Conic Theme keywords: Digital Orthophotography, Land use or land cover, Emergency management, Miscellaneous, Planimetric, Economic development, Environment, Wetlands, Infrastructure or ground transportation, Tourism or recreation, imageryBaseMapsEarthCover |
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Abstract:
Loudoun County annually obtains leaf-off, black and white, aerial imagery in the spring. Since 2004, the County has scanned this imagery to support the development of an annual digital orthophoto base. These files contain 1-foot ground-resolution, 8-bit Panchromatic, orthorectified aerial image map products in GeoTIFF version 6.0 file format. GeoTIFF files are uncompressed raster images complete with TFW coordinate information. The aerial imagery project encompasses the entire land area of the County of Loudoun, VA. Images were flown during leaf-off conditions and cover 5000' by 5000' and are tiled according to the 2002 VBMP 200-scale gridding schema (Virginia Geographic Information Network). |
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Metadata elements shown with blue text are defined in the Federal Geographic Data Committee's (FGDC) Content Standard for Digital Geospatial Metadata (CSDGM). Elements shown with green text are defined in the ESRI Profile of the CSDGM. Elements shown with a green asterisk (*) will be automatically updated by ArcCatalog. ArcCatalog adds hints indicating which FGDC elements are mandatory; these are shown with gray text.
Loudoun County annually obtains leaf-off, black and white, aerial imagery in the spring. Since 2004, the County has scanned this imagery to support the development of an annual digital orthophoto base. These files contain 1-foot ground-resolution, 8-bit Panchromatic, orthorectified aerial image map products in GeoTIFF version 6.0 file format. GeoTIFF files are uncompressed raster images complete with TFW coordinate information. The aerial imagery project encompasses the entire land area of the County of Loudoun, VA. Images were flown during leaf-off conditions and cover 5000' by 5000' and are tiled according to the 2002 VBMP 200-scale gridding schema (Virginia Geographic Information Network).
This annual digital ortho effort is implemented and administered by the Loudoun County Office of Mapping and Geographic Information. While primarily developed to capture annual base planimetric, environmental, and topographic updates throughout the County, the backdrop image can also serve as a reference layer for GIS analysis, Computer-aided Dispatching and E-911 services, Staff planning and development, historical record in land use/land cover change, and has the potential for use in many other public service projects.
Data are stored in the corporate ArcSDE Geodatabase as a raster feature class. SDE geotabase imagery is available in the County's GIS, whereas copies of source files are provided for public distribution. The coordinate system is Virginia State Plane (North), Zone 4501, datum NAD83 HARN. Digital Terrain Models were collected for the purposes of orthorectification.
ground condition
These data were generated for use by Loudoun County and are available to the public. This image data has been developed using procedures designed to produce data to National Standard for Spatial Data Accuracy (NSSDA) and is intended for use at 1:2400 scale or smaller. Acknowledgement of Loudoun County would be appreciated in products derived from this data. Every reasonable effort has been made to assure the accuracy of these data. Loudoun County, Virginia does not assume any liability arising from the use of these data. These data are provided without warranty of any kind, expressed or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular service. Reliance on these data is at the risk of the user.
1 Harrison St. SE, 3rd Floor
PO Box 7000
"March 2007 Photography flown by AirPhotographics, Inc., Martinsburg, WV." "Digital Orthophotography compiled by Infotech Enterprises America, Inc., Sterling, VA"
Where there is no data present, null data will be calculated as 255. All data was delivered "as-is" without removal of strings or other image artifacts. There will be no overedge on the deliverable orthophoto tiles.
The dataset contains raster images of digital orthophotography so the logical consistency report is not applicable. The file naming convention is based on the lower left/southwest corner of the image. Tile names are 17 characters long with a 3 character extension. An example tile name is: 07_DO_N17_7082_20.TIF. The first two characters represent the year of photography, ('07' = 2007). The next two characters represent the product code (DO = digital orthophotograph, TM = terrain model). After an underscore to separate the code, the following three characters are the Prefix to maintain uniqueness in the project. The first character indicates the state plane zone (N = North, S = South), and the next two numbers indicate the coordinate pairing of the million units of the Easting and Northing coordinates for the lower left/southwest corner of the tile.
The remaining numbers are duplicated from the same grid system emplyed in 2002 VBMP program at Virginia Geographic Information Network. An underscore separates the Prefix from the BMU (Base Modular Unit) of the next four numbers. The Base Modular Unit designates the name for 1:4800 scale imagery tiles which correspond to a 10,000 foot grid based on even 10,000 increments of the Virginia State Plane. Following another separator is a two number suffix. The first digit of the Suffix number designates the quadrant of the BMU that a nested 5,000 foot tile grid occupies. Quadrants are numbered from 1 to 4 starting with the Lower Left quadrant of the BMU, increasing in a clockwise direction. The second digit of the Suffix number designates the quadrant of the 5,000 foot tile that a nested 2,500-foot tile grid occupies. Quadrants are numbered from 1 to 4 starting with the Lower Left quadrant and increasing in a clockwise direction.
The project consisted of a total of 684 total images in the Virginia North State Plane Zone for 1' = 200' scale imagery.
A random sampling method was utilized to locate 29 points over the Phase 4 Project area to be used in the accuracy assessment. Previously measured or surveyed points were used as a reference points.The resultant accuracy of the measurements yield a circular RMSE of 1.8 US Survey feet in the horizontal domain. Measured at a 95 percent confidence level, any point measured will be within 3.1 US Survey feet in the horizontal domain.
Compiled to meet 3.1 feet horizontal accuracy at 95 % confidence level in accordance with National Standards for Spatial Data Accuracy (NSSDA).
Not Available
scanned film was then georeferenced and mosaicked by Infotech.
1. API scanned B/W photo negatives at 14 microns in Tiff/Jpeg format.
2115 Kelly Island Road
http://www.airphotographics.com/
2. Infotech performed DAT on the supplied scans using the ground control points from 2002 and 2006 Virginia Base Map Program (VBMP) within Loudoun County. 3. Using the DAT solution and updated DTM, orthophotos were generated at 1ft resolution. 4. The orthos were color balanced and then mosaiced using seamlines. 5. The mosaics were checked and corrected for any color differences, bridge distortions, etc. 6. The mosaics are cropped according to the VBMP tile grid with standard VBMP naming convention with the prefix 07 (to identify the year of photography). 7. The tiles were submitted in TIFF format with ESRI compatible world files. 8. A full mosaic of all the ortho photos is created in MrSID MG3 format with 10:1 compression ratio.
100 Carpenter Drive Suite 200
A batch proccess is run using shell script and SDE command line to load 684 geoTIFF image files from DVD to SDE instance using a compression routine.
Metadata imported.
1 Harrison Street, S.E., 2nd Floor
PO Box 7000
Every reasonable effort has been made to assure the accuracy of these data. Loudoun County, Virginia does not assume any liability arising from the use of these data. These data are provided without warranty of any kind, expressed or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular service. Reliance on these data is at the risk of the user.
Size limit: 4.5 GB. Visit our website at: http://www.loudoun.gov/omagi, click on "Loudoun County Mapping Documents & Order Forms." The "Forms" directory will lead you to custom & standard (countywide) data order forms. Hardcopy maps may also be available; please contact the Mapping Office Public Information Counter for more information regarding all data requests.
1 Harrison Street, S.E., 2nd Floor
PO Box 7000