Sam’s Greenstone Blog 26/11/2011

admin. Saturday, November 26th, 2011.

This week has mostly been spent improving Greenstone 3’s capability to display paged documents. This has mostly involved upgrading the table of contents functionality to better handle documents with a lot of pages and also have names like “Page 1”, “Page 2”, “Page 3” etc. making them virtually indistinguishable by their names. In this case it would be much better if images of the pages were displayed. Fortunately many of these collections will already have these thumbnails available so these will now be displayed in the table of contents instead of their names. Simply replacing the names with images however results in two more problems. The first is that a lot of images take up a lot of space on the page, and the second problem is that it greatly increases the amount that the user has to download from the server for each page. Even though a single black and white thumbnail is likely only to be around 10KB in size, having a thousand of these (which is not unrealistic), or if the images are color then they can quickly add up in size.

To solve both of these problems I decided that a good option would be to create a box in the table of contents that only shows a few pages at a time and can be scrolled from right to left to go through the images of the pages. As well as saving space, this approach also has the added benefit that images do not need to be loaded until they are visible within the box (i.e. they have been scrolled over). So I have implemented it so that images are loaded dynamically as necessary.

I have also added a new feature to Greenstone 3 that may prove useful in improving some of the interactions that happen between XSLT and Javascript. One thing I have been needing to do a reasonable amount recently is take parts of pages and add them to other pages. Our current method for doing this is to get the page we want and to “cut” the detail we want out of it. To hopefully smooth out this interaction I have added the ability for XSL templates to be specified in the CGI arguments given to the page. This allows Javascript AJAX calls to single out the exact part of the page they want or even create new information, all in a single AJAX call.

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