function click(d3_event, d) {
        var service = getService();
        if (!service) return;

        // try to preserve the viewer rotation when staying on the same sequence
        if (d.sequenceKey !== _selectedSequence) {
            _viewerYaw = 0;  // reset
        }
        _selectedSequence = d.sequenceKey;

        service
            .ensureViewerLoaded(context)
            .then(function() {
                service
                    .selectImage(context, d.key)
                    .yaw(_viewerYaw)
                    .showViewer(context);
            });

        context.map().centerEase(d.loc);
    }
click() Handles 'bubble' point click event.