I found why this error message happened, but the problem was not yet solved. I changed the arrays in the pos, . pos=[[0,1],[0,1],[0,1],[0,1]] ; before pos=[[0,-1],[0,-1],[0,-1],[0,-1]] ; after. However, the output image bands were still all black. I may have problems in arrays in the pos... In envi help, pos was explained... ----- Use this keyword to specify an array of long integers representing band positions to include in the mosaic. The dimensions of the array must be [#output bands, #files]. A value of -1 indicates that no input band for the associated file is included in the corresponding mosaicked output band. The valid values for POS are 0 to num_bands (for the corresponding file), or -1. ----- However, this description is not straightforward to me. In my case, I have four files with a band in each of them. The size of these files are identical. In the description, "pos must be [#output bands, #files]" Then... why not "pos [1.4]" ? When I tried these numbers, I got this error message. ----- ENVI Retrieve Data: An error has occurred during processing. Error: "Attempt to subscript with is out of range." The result may be invaild. ----- Please give me any suggestions for appropriate values in pos array. [QUOTE]kim4ecohydro wrote Hello, All! I am trying to mosaicking 4 MODIS tiles into one. I tried to use 'mosaic_doit' function. I followed the guidelines, but I got stuck in this error message. ----- ENVI Retrieve Data: An error has occurred during processing. Error: "Attempt to subscript with is out of range." The result may be invaild. I have no idea what this means. Is there anyone to help me? Please give me any comments or suggestions. This is what I have done so far. Basic idea of this souce code was from... ---------------------- pro Mosaic_062511 ; Path designation input_path = 'I:\MODIS\HDF\2008\MOD13\Mosaic\MOD13A2\' output_path = 'I:\MODIS\HDF\2008\MOD13\Mosaic\MOD13Mosaic\' for h = 0, 0 do begin date = 16 * h + 1 print,'Processing MODIS images of DOY', date dir=input_path cd,dir files=FILE_SEARCH('MOD13A2.A2008'+strtrim(string(date, format='(I03)'), 2)+'.h*.hdf', count=num_inputfiles) print, ' files = ' , files ;MODIS grid file ;format='MOD13A2.A2008001.h27v04.005.2008019050117.hdf' ;START IMPORTING MODISTILES for i=0,num_inputfiles-1 do begin grid_file=files[i] print, 'grid_file = ', grid_file ;output_rootname = 'Landinputs_'+strtrim((strmid(grid_file,9,7)+'_'+strmid(grid_file,17,6)),2)+'_' output_rootname = 'MOD13A2_'+strtrim((strmid(grid_file,9,7)+'_'+strmid(grid_file,17,6)),2) year=strmid(grid_file,9,4) grid_name = 'MODIS_Grid_16DAY_1km_VI' sd_names = ['1 km 16 days NDVI'] out_method = 0 convert_modis_data, in_file=grid_file, out_path=output_path, out_root=output_rootname, $ /higher_product, /grid, gd_name=grid_name, sd_names=sd_names, out_method=out_method,background=255;, fill_replace_value=255 print, 'output_rootname = ', output_rootname endfor cd,output_path inputs = file_search('MOD13A2_2008'+strtrim(string(date,format='(I03)'), 2)+'*.img', count=inputfiles) print,'inputfiles', inputfiles fids=lindgen(inputfiles) for i=0, inputfiles-1 do begin envi_open_file,inputs[i],r_fid=afile fids[i]=afile endfor numfiles=n_elements(fids) if numfiles eq 4 then begin ;*******START MOSAIC pos=[[0,1],[0,1],[0,1],[0,1]] out_ps = [926.6254331, 926.6254331] use_see_through = [[1L],[1],[1],[1]] see_through_val = [[0L],[0],[0],[0]] ;bandnames=['1 km 16 days NDVI'] out_name='Mosaic_MOD13_'+strtrim(string(date,format='(I03)'), 2)+'.img' print, 'output_name = ' , out_name georef_mosaic_setup, fid=fids, out_ps=out_ps, dims=dims, xsize=xsize, ysize=ysize, x0=x0, y0=y0, map_info=map_info envi_doit,'mosaic_doit',fid=fids,pos=pos,dims=dims,x0=x0,y0=y0,background=0,out_dt=2,map_info=map_info,/georef, $ xsize=xsize, ysize=ysize, pixel_size=out_ps, see_through_val=see_through_val, use_see_through=use_see_through, out_name=out_name, r_fid=mosaic ;******REMOVE FIDS AND DELETE INPUTS for i=0,numfiles-1 do begin envi_file_mng, id=fids[i],/remove; ,/delete endfor endif print, "C'est fini!! It's done!!!" endfor end ------ Reference for source code: http://www.rhinocerus.net...unning-abruptly.html [/QUOTE]

If there are 4 files with 1 band each then POS would be: pos=[[0],[0],[0],[0]] setting POS like this means there are 2 bands in each file: pos=[[0,1],[0,1],[0,1],[0,1]]