One of the most fascinating things you can do with gigapixel images is, to annotate the panorama and create a "guided tour" within the image.
I worked out how to control Microsoft HDView by injecting new view parameters with Javascript.
This is fairly easy to implement, so here is an example:
http://hdview.at/200706_gmunden2/index.html
Choose a name from the drop-down list and press the "Show me!" button. This will change the viewport to the selected feature.
