/** return a list of included images*/
QStringList GeoImageList::list(QString type)
{
    if (type.isEmpty())
        return list_;
    QStringList list;
    QStringList::ConstIterator it;
    for (it = list_.begin(); it != list_.end(); ++it) {
        GeoImage *im = geoImage(*it);
        if (QString::compare(im->type(), type, Qt::CaseInsensitive) == 0)
            list += (*it);
        qDebug("GeoImageList::list(item=%s)", it->toLatin1().constData());
    }
    return list;
}