def load_external_file(filename):
IDL.run('envi')
name, ext = os.path.splitext(os.path.basename(filename))
if ext in ['.tif', '.tiff']:
IDL.ENVI_OPEN_DATA_FILE(filename, TIFF=1)
elif ext in ['.txt', '.met']:
IDL.ENVI_OPEN_DATA_FILE(filename, LANDSAT_METADATA=1)
