An Offline Browser For GAIA Data

With some minor modifications it should be possible for the GAIA browser to work in an offline mode, accessing all images from disk.

Changes required

The following changes from standard behaviour are required. Other changes may be necessary.

Data availability

Assume all data is available.
It may be possible to test if a image is available by making a HEAD request and checking the response.

No palettes or image orientation

Palette mapping and image orientation is performed on-the-fly by the palette PHP script. Without network access this service is not available. A strftime format specifier denoting the image filenames (relative to the project's data directory) is already exists in the web services. An offline browser could access the unprocessed image files directly.
Allow user to define the location of the data directory. Browser should accept a query parameter to define the directory.

Do not display palette or image orientation options

They will not function so they should not be displayed. Easy to do on with style sheets when the page has loaded.

Implementation comments

• How to decide if browser is in offline mode? Maybe document.location.protocol?
• Create a tool for the toolbox to allow users to configure the data directory?
• Will cookies work for file: URLs?
• Is it possible to make a (HEAD) XMLHttpRequest to determine if a file exists (when using the file: protocol)?
  No, it seems not.

Links

• A JavaScript ZIP library: http://helma.zumbrunn.net/reference/helma/Zip.html. Might be useful but cannot see how to insert data into an img tag. Maybe an object tag could be used instead?

-- SteveMarple - 08 Apr 2007