OpenSeadragonImagingHelper

OpenSeadragonImagingHelper is a plugin for OpenSeadragon which implements some properties and methods helpful in imaging applications.

View the Documentation

Demo/Test Site

Usage

Prerequisite note: OpenSeadragonImagingHelper requires OpenSeadragon version 2.0+.

The OpenSeadragonImagingHelper bundle can be obtained the following ways:

1. Direct download openseadragon-imaginghelper.js (and optionally openseadragon-imaginghelper.js.map)
2. npm

    npm install @openseadragon-imaging/openseadragon-imaginghelper

The OpenSeadragonImagingHelper bundle can be included using a script tag in HTML or imported as a library module (ES2015, CommonJS, AMD).

An ImagingHelper object can be created and attached to an OpenSeadragon.Viewer two ways:

1. Call the activateImagingHelper method on the viewer
2. Create a new ImagingHelper object, passing a viewer reference in the options parameter

Both methods return a new ImagingHelper object, and both methods also add the ImagingHelper object reference to the viewer as a property called 'imagingHelper'.

Example using an HTML script tag

<script
  type="text/javascript"
  src="path_to/openseadragon/openseadragon.js"
></script>
<script
  type="text/javascript"
  src="path_to/openseadragon-imaging/openseadragon-imaginghelper.js"
></script>

    // Example 1 - Use the Viewer.activateImagingHelper() method to create an ImagingHelper

    // create an OpenSeadragon viewer
    var viewer = window.OpenSeadragon({...});
    // add an ImagingHelper to the viewer
    var imagingHelper = viewer.activateImagingHelper({...});


    // Example 2 - Attach a new ImagingHelper to an existing OpenSeadragon.Viewer

    var imagingHelper = new window.OpenSeadragonImaging.ImagingHelper({viewer: existingviewer});

Example importing as a module

    npm install openseadragon --save
    npm install @openseadragon-imaging/openseadragon-imaginghelper --save

import OpenSeadragon from 'openseadragon';
import OpenSeadragonImagingHelper from '@openseadragon-imaging/openseadragon-imaginghelper';

    // Example 1 - Use the Viewer.activateImagingHelper() method to create an ImagingHelper

    // create an OpenSeadragon viewer
    var viewer = OpenSeadragon({...});
    // add an ImagingHelper to the viewer
    var imagingHelper = viewer.activateImagingHelper({...});


    // Example 2 - Attach a new ImagingHelper to an existing OpenSeadragon.Viewer

    var imagingHelper = new OpenSeadragonImagingHelper({viewer: existingviewer});

Details

The ImagingHelper class provides a simplified zoomFactor which is simply the ratio of the displayed image pixel size to the image's native pixel size.

In OpenSeadragon 2.0 and above, conversion is based on the image at index 0 in world.getItemAt, unless another value is set by the worldIndex option.

The ImagingHelper methods use three coordinate systems, named as follows:

1. physical: Device pixel coordinates relative to the SeaDragon viewer
2. logical: 0.0 to 1.0 relative to the image's native dimensions
3. data: Pixel coordinates relative to the image's native dimensions

Methods are provided to zoom and/or pan using these conventions, as well as to convert individual horizontal/vertical values or point ({x,y}) objects between coordinate systems (Note: methods that return a point object return new OpenSeadragon.Point objects)

The ImagingHelper class extends the OpenSeadragon.EventSource class and raises an event named 'image-view-changed' whenever the viewer's zoom and/or pan position changes.

    // Event Example 1 - Use the options 'onImageViewChanged' property to set a handler

    var viewer = OpenSeadragon({...});
    var imagingHelper = viewer.activateImagingHelper({onImageViewChanged: onImageViewChanged});

    function onImageViewChanged(event) {
        // event.viewportWidth == width of viewer viewport in logical coordinates relative to image native size
        // event.viewportHeight == height of viewer viewport in logical coordinates relative to image native size
        // event.viewportOrigin == OpenSeadragon.Point, top-left of the viewer viewport in logical coordinates relative to image
        // event.viewportCenter == OpenSeadragon.Point, center of the viewer viewport in logical coordinates relative to image
        // event.zoomFactor == current zoom factor
        ...
    }


    // Event Example 2 - Add a handler to an existing ImagingHelper

    imagingHelper.addHandler('image-view-changed', function (event) {
        // event.viewportWidth == width of viewer viewport in logical coordinates relative to image native size
        // event.viewportHeight == height of viewer viewport in logical coordinates relative to image native size
        // event.viewportOrigin == OpenSeadragon.Point, top-left of the viewer viewport in logical coordinates relative to image
        // event.viewportCenter == OpenSeadragon.Point, center of the viewer viewport in logical coordinates relative to image
        // event.zoomFactor == current zoom factor
        ...
    });

Demo/Test Site

The demo site is an example using ImagingHelper in a React application. The page displays many OpenSeadragon and OpenSeadragonImagingHelper metrics, as well as the output of many OpenSeadragonImagingHelper methods, all in real-time as the cursor moves and/or the image is zoomed/panned.

The source code can be found here.

Legacy Demo/Test Site

The old demo site is still available here. This page adds an example of syncing an SVG overlay for annotation support.

All the sample code is in scripts/viewmodel.js.

TODO

1. Better multi-image support