There is also a plugin to do this: ImageBoundary. To speed up, create pyramids (overview). All the best.
Il giorno lun, 24/01/2011 alle 17.04 +0000, Saber Razmjooei ha scritto: > I guess it's better to be done in GRASS. -- http://www.faunalia.it/pc _______________________________________________ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
