This example shows how to use the GeoExt.component.OverviewMap class.

The overviewmap will visualize the extent of the main map with a rectangle. The main map can be rotated (using SHIFT & drag), and the overviewmap will adjust the rotation of the rectangle. The top-left corner is visualized with a circle in the overviewmap.

Have a look at overviewMap.js to see how this is done.