DOQQ 1994 (aerial photos-Image Server)

Orthophotos combine the image characteristics of a photograph with the geometric qualities of a map. The primary digital orthophotoquad (DOQ) is a 1-meter ground resolution, quarter-quadrangle (3.75-minutes of latitude by 3.75-minutes of longitude) image cast on the Universal Transverse Mercator Projection (UTM) on the North American Datum of 1983 (NAD83).The geographic extent of the DOQ is equivalent to a quarter-quad plus The overedge ranges a minimum of 50 meters to a maximum of 300 meters beyond the extremes of the primary and secondary corner points. The overedge is included to facilitate tonal matching for mosaicking and for the placement of the NAD83 and secondary datum corner ticks. The normal orientation of data is by lines (rows) and samples (columns). Each line contains a series of pixels ordered from west to east with the order of the lines from north to south. The standard, archived digital orthophoto is formatted as four ASCII header records, followed by a series of 8-bit binary image data records. The radiometric image brightness values are stored as 256 gray levels ranging from 0 to 255. The metadata provided in the digital orthophoto contain a wide range of descriptive information including format source information, production instrumentation and dates, and data to assist with displaying and georeferencing the image. The standard distribution format of DOQs will be JPEG compressed images on CD-ROM by counties or special regions. The reconstituted image from the CD-ROM will exhibit some radiometric differences when compared to its uncompressed original but will retain the geometry of the uncompressed DOQ. Uncompressed DOQs are distributed on tape. Please contact [e-mail] for more information.正射影像（Orthophoto）兼具摄影图像的成像特质与地图的几何精度特性。主流的数字正射影像四分之一图幅（DOQ）采用1米地面分辨率，覆盖范围为纬度3.75分×经度3.75分的四分之一标准图幅，投影方式为基于1983北美大地基准面（NAD83）的通用横轴墨卡托投影（UTM）。该类DOQ的地理覆盖范围等效于标准四分之一图幅，且在主、辅角点的极值边界外，额外覆盖50米至300米不等的边缘冗余数据。设置该边缘冗余数据旨在便于影像镶嵌时的色调匹配，以及标注1983北美大地基准面与辅助大地基准面的角点标记。数据的常规排布形式为行（lines）与列（samples）：每行像素按自西向东的顺序依次排列，各行则按照自北向南的顺序排布。标准归档的数字正射影像采用如下存储格式：前4条记录为ASCII头文件，后续为一系列8位二进制影像数据记录。影像的辐射亮度值以0至255共256个灰度级进行存储。数字正射影像附带的元数据包含多类描述性信息，涵盖格式源信息、生产设备与生产日期，以及辅助影像显示与地理配准的相关数据。DOQ的标准分发格式为以县或特定区域为单位、存储于只读光盘（CD-ROM）的JPEG压缩影像。从光盘读取的重构影像相较于未压缩的原始影像会存在一定辐射差异，但可完整保留未压缩DOQ的几何精度。未压缩的DOQ通过磁带进行分发。如需获取更多信息，请联系邮箱[e-mail]。