envi_open_file,fna,r_fid=fid
envi_file_query,fid, ns=ns, nl=nl, nb=nb, dims=dims, data_type=data_type, interleave...=interleave, offset=offset
map_info=envi_get_map_info(fid=fid)
b3= ENVI_GET_DATA(fid=fid, dims=dims,...apr_nir+apr_r)
o_fn='D:\idl\526.tif'
envi_write_envi_file,ndvi,out_name=o_fn,ns=ns,nl=nl,nb=1,data_type=4,interleave