Photogrammetric scans of aerial photographs of North American glaciers, 1992. Roll 4 jpegs

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. File 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 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 (this 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 or matchReport.txt) with color information and scanner specifications unique to each image.

## 数据集简介
1958年至1999年间，奥斯汀·波斯特（Austin Post）主持美国地质调查局（United States Geological Survey, USGS）的北美冰川航空影像采集工作。该批影像以垂直立体黑白影像为主，同时亦采集了单幅倾斜影像与彩色影像，采集对象为北美冰川。本平台提供的数字化成果旨在记录近50年来这些冰川的变化历程，本项目的核心目标是将这些胶片影像中的数据以数字化形式永久保存，以供后续开展北美冰川变化相关的研究分析。

## 文件布局
1. **一级目录**：包含1964年至1997年的全量影像元数据文件（nagapData.csv），以及用于指导数据检索与子集提取的R脚本（searchData.R）；另有fileLayout.pdf文件以可视化形式展示整体文件结构与目录内容，此外还包含3个按年代划分飞行路径信息的KML文件。
2. **二级目录**：以影像拍摄年份命名，涵盖1964年至1997年的32个拍摄年份。多数目录内包含由奥斯汀·波斯特撰写注释说明的JPEG影像文件，同时还包含对应年份的专属元数据CSV文件（YYYY.csv），其中存储了全年影像的完整元数据信息，包括拍摄日期、胶卷编号、地点名称、经度、纬度、飞行高度、介质类型与备注。全量元数据文件（nagapData.csv）即为各年份专属CSV文件的汇总集合。
3. **三级目录（即当前层级）**：存储冰川影像数据。本层级目录按相机胶卷编号（1、2等）与影像类型（缩略图、JPEG或TIFF）进行划分，部分目录还包含框标影像与倾斜影像子目录。本层级主要存储各类格式的航空影像文件，包括缩略图、JPEG与TIFF格式；此外还包含针对各胶卷的专属元数据CSV文件（包含拍摄日期、胶卷编号、地点名称、经度、纬度、飞行高度、介质类型与备注）、存储单幅影像专属相机参数的文本文件（info.txt），以及包含单幅影像色彩信息与扫描仪参数的文本文件（histo.txt或matchReport.txt）。