Photogrammetric scans of aerial photographs of North American glaciers, 1974

Introduction: Between 1958 and 1999, Austin Post led the USGS collection of aerial imagery of North American glaciers. These images are primarily vertical stereo black and white images, although single oblique images, as well as color images have been collected. The glaciers of North America were the subjects, and the digital products made available here serve to document the changes that have occurred to the glaciers over the past 5 decades. The purpose of this project is to preserve the data contained within these film images in a digital format for future analysis of North American glacier change. Package Layout: 1. The first level contains an overall data set of image metadata from 1964 - 1997 (nagapData.csv) and an R script (searchData.R) with instructions on how to search and subset the data. fileLayout.pdf shows the file structure and folder contents visually. There are also three kml files with flight path information by decade. 2. The second level (this level) is the year in which the pictures were taken. There are 32 years with images from 1964 – 1997. The majority of these folders are jpegs with notes provided by Austin Post. They also contain a year-specific csv (YYYY.csv) that contains image metadata for the entire year (date, roll numbers, location name, longitude, latitude, altitude, media, and comments). The overall data set (nagapData.csv) is the aggregate of each individual “YYYY.csv” file. 3. The glacier photos are located at the third level. The folders at this level are distinguished by camera roll number (1, 2, etc.), and image type (thumbnail, jpeg, or tif); some also contain fiducial and oblique image folders. This level primarily contains image files of aerial photos as either thumbnails, jpegs, or tifs. It also includes a csv with image metadata specific to each roll (date, roll numbers, location name, longitude, latitude, altitude, media, and comments), a text file (info.txt) with camera specifications unique to each image, and a text file (histo.txt) with color information unique to each image.

引言：1958年至1999年间，奥斯汀·波斯特（Austin Post）主持了美国地质调查局（United States Geological Survey, USGS）的北美冰川航空影像采集工作。本次采集的影像以垂直立体黑白航空影像为主，同时也收录了单幅倾斜影像与彩色影像。数据集以北美冰川为研究对象，此处开放的数字化成果用于记录近50年来北美冰川发生的变化。本项目旨在将这些胶片影像中的数据以数字化格式保存，为后续开展北美冰川变化研究提供支撑。

数据包结构：
1. 一级目录包含1964年至1997年的全域影像元数据集（nagapData.csv），以及用于指导数据检索与子集筛选的R脚本（searchData.R）。fileLayout.pdf以可视化形式展示了文件结构与文件夹内容。此外还包含3个按年代划分飞行路径信息的KML（Keyhole Markup Language）文件。
2. 二级目录（即当前层级）为影像拍摄年份，涵盖1964年至1997年的32个年份。大部分文件夹内存储了奥斯汀·波斯特撰写说明的JPEG（Joint Photographic Experts Group）图像，同时还包含对应年份专属的逗号分隔值文件（YYYY.csv），其中收录了全年影像的元数据，包括拍摄日期、相机胶卷编号、地点名称、经度、纬度、拍摄高度、介质类型与备注信息。全域数据集（nagapData.csv）为各年份"YYYY.csv"文件的汇总集合。
3. 冰川影像位于三级目录。该层级的文件夹以相机胶卷编号（1、2等）与影像类型（缩略图、JPEG或TIFF（Tagged Image File Format））进行区分，部分文件夹还包含框标影像与倾斜影像子文件夹。本层级主要存储航空影像的数字化文件，格式涵盖缩略图、JPEG或TIFF。此外还包含针对每个胶卷的专属影像元数据CSV文件（包含拍摄日期、胶卷编号、地点名称、经度、纬度、拍摄高度、介质类型与备注信息）、记录单幅相机专属参数的文本文件（info.txt），以及记录单幅影像专属色彩信息的直方图文本文件（histo.txt）。