I have a polygon shapefile with several attributes. One Attribut is a number which represents a landuse class which was created by ground truth data. Now i want to do a supervised classification using maximum likelihood and I want to use this attribut of my shape file to define my training regions. Here I struggle. When I load my shapefile every polygon is a single region and I don't see how I can group them by the same attribut. I saw that Envi Fx has the option to use ground tuth attributs to group feature classes, but I'm looking for a similar way in the maximum liklehood workflow...