Loudoun Imagery 1986

Loudoun County has collected aerial imagery for many years. While imagery has been captured in digital format since the mid-2000s, prior years were captured with film cameras. Rolls of film from previous years were available at the County in film canisters, but unavailable for viewing on modern digital GIS systems. The County initiated a project to have these film rolls scanned into a digital format. The film was then processed using modern photogrammetric techniques to produce a digital orthomosaic of the County. Images from 1979, 1986, 1988, 1990-2007 were processed and delivered as tiled uncompressed GeoTIFF and MrSID mosaic formats. 1979, 1986, and 1988 were captured and produced as color (R,G,B) images, while the remainder were captured and produced as panchromatic (B/W) images. The MrSID mosaics use a 50:1 compression ratio. Approximate seamline locations containing the scan name attribute have also been provided. The aerial imagery generally encompasses the full land area of the County of Loudoun, VA. Images were flown in varying temporal and ground conditions and will exhibit some variation in tone, quality, and positional accuracy. "Digital Orthophotography compiled by Sanborn Map Company, Inc. Colorado Springs, CO"劳登县（Loudoun County）多年来持续收集航空影像。2000年代中期起，影像以数字格式采集，而此前的影像均采用胶片相机拍摄。此前年份的胶片卷以胶片罐形式保存在该县，但无法在现代数字地理信息系统（Geographic Information System，GIS）上直接查看。该县启动专项项目，将这批胶片卷扫描为数字格式。随后，借助现代摄影测量技术对扫描后的影像进行处理，生成劳登县的数字正射镶嵌图（digital orthomosaic）。1979年、1986年、1988年以及1990年至2007年的影像均完成处理，并以分幅未压缩GeoTIFF和MrSID镶嵌格式交付。其中1979、1986及1988年的影像为彩色（红、绿、蓝，RGB）影像，其余时段的影像均为全色（黑白）影像。MrSID镶嵌图采用50:1的压缩比。同时还提供了包含扫描名称属性的近似接缝线位置数据。本次航空影像基本覆盖弗吉尼亚州劳登县的全部陆地范围。由于影像采集时的时间、地面条件存在差异，其色调、成像质量以及位置精度会存在一定波动。“数字正射影像由科罗拉多州科罗拉多斯普林斯市的桑伯恩地图公司（Sanborn Map Company, Inc.）编制”