Loudoun Imagery 1988

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"劳登县多年来持续收集航空影像数据集。自2005年中期起，影像均以数字格式采集，而此前年份的影像则采用胶片相机拍摄。过往年份的胶片卷以胶片罐形式保存于该县，但无法在现代数字地理信息系统（Geographic Information System, GIS）中查看。该县遂启动项目，将这些胶片卷扫描为数字格式。随后通过现代摄影测量技术对扫描后的胶片进行处理，生成该县的数字正射影像镶嵌图（digital orthomosaic）。1979年、1986年、1988年以及1990年至2007年的影像均已完成处理，并以分幅未压缩GeoTIFF及MrSID镶嵌格式交付。其中1979年、1986年及1988年的影像为彩色（红、绿、蓝，RGB）图像，其余年份影像均为全色（黑白）图像。MrSID镶嵌格式采用50:1的压缩比。项目还提供了带有扫描名称属性的近似接缝线位置信息。该航空影像基本覆盖弗吉尼亚州劳登县的全部陆地区域。由于影像采集时的时间环境与地面条件各不相同，其色调、成像质量与位置精度均存在一定差异。本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。