Download YAFTA.tar.gz, and unpack it via > tar -zxvf YAFTA.tar.gz This will create the directory YAFTA, containing the following items: Obsolete/ ReadMe YAFTA_IDL.pro YAFTA_Intro.pdf YAFTA_Intro.ps YAFTA_Intro.tex YAFTA_dualmask.pro YAFTA_dualmask_out.pro YAFTA_input.sav YAFTA_output.sav YAFTA_test.pro alt_mask.pro change_log.txt create_features.pro YAFTA_display.pro display_labels.pro find_nearby.pro imgexp.pro imgscl_fen.pro match_features_v01.pro match_masks.pro pad_array.pro plot_edges.pro plot_labels.pro rankdown.pro tvread.pro Read YAFTA_intro.pdf or YAFTA_intro.ps to learn more about these codes. (A program list appears near the end of these documents.) From the IDL prompt, you should be able to enter IDL> .run YAFTA_test.pro Then, as IDL commands are discussed in YAFTA_Intro.p*, you should be able to enter the IDL commands in YAFTA_IDL.pro line by line from the IDL prompt.