Loudoun Imagery 2001 (BW)

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"弗吉尼亚州劳登县（Loudoun County）多年来持续开展航空影像收集工作。自2000年代中期起，影像均以数字格式采集；而更早年份的影像则采用胶片相机拍摄。此前年份拍摄的胶片卷以胶片罐形式留存于县内档案中，但无法在现代数字地理信息系统（GIS, Geographic Information System）中直接浏览。该县启动专项项目，将这批胶片卷扫描转换为数字格式，随后利用现代摄影测量技术对扫描影像进行处理，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与MrSID镶嵌格式交付。其中1979年、1986年及1988年的影像为彩色（RGB，红、绿、蓝）图像，其余年份的影像均为全色（黑白，panchromatic）图像。MrSID镶嵌影像采用50:1的压缩比。数据集同时提供了附带扫描名称属性的近似接缝线位置信息。该航空影像数据集基本覆盖弗吉尼亚州劳登县的全部陆地范围。由于影像采集于不同的时间节点与地面环境条件下，其色调、成像质量及位置精度存在一定差异。本数据集为科罗拉多州科罗拉多斯普林斯市桑伯恩地图公司（Sanborn Map Company, Inc.）编制的数字正射摄影成果。