SkyView-in-a-Jar users will note that the new v3.2.0 SkyView jar is much smaller than the earlier versions, under 4 megabytes compared to over 15 megabytes for v3.1.21. Part of the reason is that the way we access some older surveys has been changed.
The SkyView software can look for survey data in three distinct locales: over the web using URLs, in the local file system using file names, and in the SkyView jar using resource names.
Almost all surveys use URLs. There are two special features for these. First, SkyView can notice that the URL is pointing to data on the local file system. The SkyView web site uses this to translate SkyView URLs to local file references. Second, most URLs are cached. When a user or the SkyView web site asks for a URL from, say, the SDSS, it downloads it only once. The next time that URL is requested it is retrieved from the cache. Skyview-in-a-Jar users will also cache the data from surveys stored on the SkyView machines, since for them those data are not local.
In previous versions a few survey’s data (EGRET, CompTel, nH, 1420 Mhz, 408Mhz, HEA01A2) were actually included in the jar file directly. We’ve now moved these to use URLs as above. Since these will be cached, SkyView-in-a-Jar users will only download the data once. All of these surveys are quite small and we don’t anticipate anyone will really notice the difference. The one exception is that this did allow users to test out SkyView with no network connections. This is still easy to do using the UserSurvey settings. More sophisticated
users can also provide survey description files that point to local data.
A few surveys are still provided as references to files in the local file system. This includes the Mellinger survey where our agreement is that the underlying data will not be directly visible as a URL. The other survey is the GOODSIRAC data. These data are available as URLs but it is difficult to characterize the image WCSs in a way that works with our survey description files. When specifying image URLs SkyView tries to provide enough geometry information in the description to enable the program to decide which candidate images are needed for a mosaic before downloading them. That was hard to do for this survey. As local files rather than URLs, SkyView can always use the WCS in the actual FITS file when looking at their geometry.