期刊名称：ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences
印刷版ISSN：2194-9042
电子版ISSN：2194-9050
出版年度：2002
卷号：XXXIV Part 4
出版社：Copernicus Publications
摘要：The CGDI (Canadian Geospatial Data Infrastructure) currently supports access to the CDAL (CGDI Data Alignment Layer) data via a public Web site, however, the process to retrieve the data is designed for human interaction and is not available programmatically as an online service. Furthermore, retrieval of individual, or an arbitrary range of points is not currently supported by the CDAL, and instead complete data sets have to be requested, where a data set consists of a regular area of points based primarily on the NTS (Canadian National Topographic Sheet) system. A data set can be retrieved only one at a time by specifying its data set name or number. This paper describes a new service that supports more general access and visualization of the CDAL data. The new CDAL system is an online service and provides easy access to a database of ground control points. The clients of this service are able to obtain responses in either HTML or XML format and to request CDAL data in either a textual or graphical form. The service accepts HTTP requests that permit a geographic region of interest to be specified as the search criteria. Only those points found within the region of interest will be returned. The second service, built on the first one, uses the textual information associated with CDAL ground control points to deliver rasterized image chips rendered for visualizing points of the CDAL
