I want to mosaic two image together, every image is 5097*5097, and they are declining. So when specify x0 ,y0, xsize, ysize, I calculate them firstly. But my program doesn't work. Could you help me? My code is below: //////////////////////////////////////////////////////////////// envi_open_file, 'F:\mosaic\sz02-02.tif', r_fid = sz02_fid if(sz02_fid eq -1) then begin envi_batch_exit return endif envi_open_file, 'F:\mosaic\sz03-02.tif', r_fid = sz03_fid if(sz03_fid eq -1) then begin envi_bathc_exit return endif envi_file_query, sz02_fid, ns=sz02_ns, nl=sz02_nl envi_file_query, sz03_fid, ns=sz03_ns, nl=sz03_nl dims = [[-1,0,sz02_ns-1,0,sz02_nl-1],[-1,0,sz03_ns-1,0,sz03_nl-1]] fids = [sz02_fid, sz03_fid] pos = [[0,-1,-1],[0,-1,-1]] out_ps = [1.,1.] out_name = 'test.img' xsize = 5193L ysize = 10102L x0=[195,97] y0=[1,5002] map_info = envi_get_map_info(fid=sz02_fid) use_see_through = [[1L],[1]] see_through_val = [[0L],[0]] envi_doit, 'mosaic_doit', fid=fid, pos=pos, $ dims=dims, out_name=out_name, xsize=xsize, $ ysize=ysize, x0=x0, y0=y0, /georef, map_info=map_info, $ out_dt=2, pixel_size=out_ps, $ background=255, see_through_val=see_through_val, $ use_see_through=use_see_through envi_batch_exit end ///////////////////////////////////////////////// many thanks