SkyView V3.2.0: Survey descriptions downloaded on demand

The biggest change in v3.2.0 of SkyView is that survey description files are no longer part of the SkyView jar. In v3.1.21 we added a small file that retained the mapping between survey names and the description files they referred to. In that version we only used the file to skip reading all of the survey description files — the user only needed to read the survey descriptions for the surveys they were interested in.

In v3.2.0 we took further advantage of this file by adding the information about when the survey description files were created to it. When a user requests a survey, SkyView looks to see if the survey is available as a local file (e.g., as it would be for the web site). If not it checks to see if there is a cached version of the file and if the cached version is newer than the version at the SkyView web site. If so this version is used. Otherwise the file is downloaded from the SkyView web site, placed in the cache and then processing continues. So users will always get have the latest version of the survey to work with.

There remains one possible problem. If a survey updates tile files without changing their names, then SkyView will not be able to tell that the cached data files are out of date. Fortunately most dynamic surveys change the names of the files (e.g., using a version identifier) when they update their tile data.

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