Photogrammetric scans of aerial photographs of North American glaciers

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: The first level (this level) contains an overall data set of image metadata from 1964 - 1997 (nagapData.csv), an R script (searchData.R) to subset and download images from this data package, and a README file with instructions for using searchData.R. fileLayout.pdf shows the file structure and folder contents visually. There are also three kml files with flight path information by decade. 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. 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 or matchReport.txt) with color information and scanner specifications unique to each image.

### 数据集介绍
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，同时也包含单张倾斜影像与彩色影像。本数据集以北美冰川为拍摄对象，此处开放的数字化成果旨在记录近50年来北美冰川发生的变化。本项目的核心目标是将这些胶片影像中的数据以数字化格式留存，以供未来开展北美冰川变化相关研究分析使用。

### 文件结构
#### 一级目录（当前目录）
包含1964年至1997年的全域影像元数据集'nagapData.csv'、用于从本数据包中筛选并下载影像的R脚本'searchData.R'，以及一份说明'searchData.R'使用方法的README文件。'fileLayout.pdf'以可视化形式展示了整体文件结构与文件夹内容。此外还有3个按十年划分飞行航线信息的KML文件。

#### 二级目录
以影像拍摄年份命名，共涵盖1964年至1997年中的32个年份。大部分此类文件夹内包含奥斯汀·波斯特标注说明的JPEG图像，同时还包含一份对应年份的专属CSV文件（'YYYY.csv'），其中存储了该年度全部影像的元数据，包括拍摄日期、胶卷编号、地点名称、经度、纬度、海拔、介质类型与备注信息。全域数据集'nagapData.csv'即由各年份单独的'YYYY.csv'文件聚合而成。

#### 三级目录
存储冰川影像。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）进行区分，部分文件夹还包含框标（fiducial）影像与倾斜影像子文件夹。本层级主要存储缩略图、JPEG或TIFF格式的航空影像文件，同时还包含一份对应每个胶卷的专属元数据CSV文件（包含拍摄日期、胶卷编号、地点名称、经度、纬度、海拔、介质类型与备注信息）、一份记录单张影像专属相机参数的文本文件'info.txt'，以及一份记录单张影像专属色彩信息与扫描仪参数的文本文件'histo.txt'或'matchReport.txt'。