Title: USDA-FSA-APFO Digital Ortho Mosaic 7.5 min Quadrangle
Originator: USDA - Farm Service Agency - Aerial Photography Field Office
Abstract:
Digital orthophotos combine the geometric qualities of a map with the image qualities of a photograph. The orthophotos in this series are a mosaic of digital orthophoto quarter quads (DOQs) produced through the National Digital Ortho Photo Program (NDOP). The image characteristics of the orthophotos in this series follow that of the source DOQs. The ground sample distance is 1 meter in the x direction and 1 meter in the y direction and the images are rectified to the UTM Coordinate System, NAD83.
The images are in GeoTIFF format and each image covers a 7.5-minute quadrangle with a 300-meter overedge between quads. The DOQs are mosaicked to remove visible seam lines due to characteristics of the source aerial photography. Mosaic cutlines are interactively defined within the DOQ image overedge by examining each DOQ pairwise with adjoining DOQs and placing the seam line where image tone differences and geometric misalignments are minimized. Due to the overedge between ortho quads, and depending on the placement of seam lines, each ortho quad can contain portions of as many as 16 DOQs. During the mosaicking process, the image tone of all input DOQs is adjusted towards a common value.
The primary purpose of the ortho quads is to support USDA Field Service Centers located in counties throughout the United States. The DOQs are edge matched or seamed across county boundaries. In counties that are split by UTM zones, ortho quads are reprojected into the predominate zone. Ortho quads may be produced and distributed in an incomplete form when constituent DOQs are not available at production date.
The naming convention for ortho quads is as follows:
sYYXXXnn.tif
where:
-- "s" denotes the status of the orthoquad: M is a complete mosaic Z is a reprojected mosaic X is an incomplete mosaic
-- YY is the degrees in latitude of the 1 degree block containing the quad.
-- XXX is the degrees in longitude of the 1 degree block containing the quad.
-- nn is the number of the quad ( 1 through 64 ) in the 1 degree block in order of west to east, north to south.
Format: Raster – 1 or 3 band GeoTIFF images with each pixel containing an 8-bit gray-scale value between 0-255.
Spatial Reference Information: Universal Transverse Mercator, North American Datum of 1983
