bejokaryo

Dear Ahmed, based on my understanding, if i'm not mistaken you can follow this step: firstly, you can perform classification if you haven't classify your data. in ENVI you can use classification from Toolbox > Classification > Supervised Classification. for urban area possibly you can also choose example based classification (in ecognition software known as object based classification). From the Toolbox, select Feature Extraction > Example Based > Feature Extraction Workflow. secondly you can select vacant land based on your classification for me it is easier using ENVI CLASSIC load your classified data Select Basic tools> region of interest>roi tools from roi tools, select vacant land class using options>band threshold to roi. fill the value with the classified data (for example vacant land has value of 5, then fill min and max with 5) then export roi to shapefile. finally you have vacant land boundary in shapefile hopefully this can help

we can use envi classic with band math. for example given band1 (b1), masked value = 0, replace value with 10. use band math (b1 eq 0)*10. then add the image with the non masked (b1 ne 0)*b1. adding both image will combine masked and non masked images. you can also directly add both using formula ((b1 eq 0)*10 + b1). eq means equal. ne means not equal. just check envi help