NCSTRL Documentation

Installing the Dienst Page-Level Zoom Package

This section of the Dienst installation instructions describes how to install the optional page-level zoom package. All directory names, except when noted otherwise, are relative to the dienst directory that you created when you downloaded the Dienst server.

Overview of zoom

The zoom option provides a point and click interface for zooming in on an area of a viewed page. When the option is enabled, a user can click on a detail of interest. The detail is centered and displayed in an enlarged format. The quality of the enlargement depends on the resolution of the original document. The feature is useful for viewing small type in equations and resolving fine print in diagrams.

Prerequisites for this installation

To install the zoom package, you must have previously installed a basic Dienst system and added document types for images in inline GIF format. To really take advantage of the zoom feature you need high resolution documents in scanned TIFF format. Note that the TIFF documents are in addition to the GIF documents. This is because Web servers can display only GIF images inline. The zoom routines require that you have Jeff Poskanzer's PBM libraries and Sam Leffler's TIFF library. The latter is needed only if you use the TIFF format. As is the case with the basic installation, you will need a working knowlege of perl and Unix to complete this installation.

Overview of this installation

If you have only inline GIF documents you need only install the zoom software for GIF. For good quality zooming, you need documents of high resolution. If all of your documents also have a scanned TIFF representation, you need only install the software for TIFF. If some, but not all, of your documents have a TIFF representation you need to install the software for both GIF and TIFF.

The installation procedure includes the following steps:

  1. Installing zoom software for TIFF - modify and compile the zoom routines.
  2. Enabling the zoom option - configure Dienst to allow zooming.
  3. Configuring your CERN Web server - add a line to enable the zoom option.

Detailed installation instructions

Installing the zoom software for TIFF files

These zoom routines automatically crop a rectangular region of a TIFF image and convert the result to a GIF image for inline display. The cropped region is centered on a user-selected point of the corresponding GIF page.

The source files for the TIFF zoom utility reside in the Utilities/src/tiffcrop2gif directory. Compile the executable using the Makefile. The Makefile uses the gcc compiler and assumes that the PBM and TIFF libraries are on the load path for the compiler, or are in the directory Utilities/lib. If you need to install these libraries on your system, you can place them in Utilities/lib. The binary is automatically installed in Utilities/bin. The utility itself does not assume a particular resolution for the input TIFF files or output GIF files; the constants that define the resolutions must be set in the pre-installation configuration file Config/option_zoom.config as described in the next section.

Enabling the zoom option in Dienst

The Dienst pre-configuration file Config/install.config contains a tagged variable that you must change to enable zoom on your server. The value of this variable is the name of the zoom option configuration file. It should look like this:
Next, edit this zoom options configuration file: Config/option_zoom.config. Make sure that zoom_enable is true, and that the other variables are correct for your scanned images:

When you have finished editing this file, run perl -c <> to check for syntax errors. Next, from the Config directory, type (If you need a review of the autoconfiguration process, check out the basic installation instructions .) Finally, "reload" the dienst code with a kill -USR1 signal to the current Dienst process.

Configuring your CERN Web server for the zoom option

If you use an NCSA Web server you don't need to read this. If you use a CERN Web server you must add the following line to the URL translation rules of the httpd configuration file to give Dienst access to the tmp directory that the temporary zoom images are stored.
    Pass   /tmp/*   <path>/dienst/tmp/*
Remember to send a kill -HUP to the CERN server to force it to reload the httpd config file.

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