It looks like a bug in the example code.  The ENVI_GLT_DOIT should take pixel_size as a scalar, not an array.  So set pixel size to: pixel_size = 1000.0D (or whatever pixel size you want) rather than pixel_size=[1000.0D] which makes it an array.  You can also leave pixel size out and let ENVI estimate it. 

Thanks a lot, now it works!  I did cut and paste  from the ENVI help, so it is kinda weird for me that the help of the software contains such errors.

Hi all, i am experimenting problems writing a code to georeference MODIS DATA. I copy and paste the code “example_glt_usage” from ENVI help in the IDL soft 6.2, I change the "[ ]" like mnimari said in the post cited, and I compile and run the code, then I select the images and next the runtime halt with the message error: “envi_built_glt_doit: An error has occurred during processing” Error: “Attempt to subscript DXS with is out of range.” The result may be invalid.   Some one experimented these error? thanks, Javier [QUOTE]m.brogioni@ifac.cnr.it wrote Hi all, I am experiencing several problems in writing a code for georeferencing satellite data (MODIS, AMSR-E and also smaller images, eg 200x200 pixels). I am using the code I found in the ENVI help (which I attached at the bottom of the post). Unfortuately, when the ENVI_GLT_DOIT command is executed I get this error: envi_built_glt_doit: An error has occurred during processing Error:"The array must be a scalar in this context: ." Results may be wrong I get this error independently of the input data. I have try to debug the code but IDL doesn't show the code (as expected). Does someone knows how to fix this problem? Thanks, Marco ____________________________________________________   example_glt_usage, eventstrictarr ; Select an image and it's associated input geometry. envi_select, title= dims=dims, fid=fid, pos=pos 'Please select an image to georeference', $ if envi_select, title= fid=x_fid, dims=dims, pos=x_pos, /band_only, /no_dims fid eq -1 then return'Please select the longitude band', $ if envi_select, title= fid=y_fid, dims=dims, pos=y_pos, /band_only, /no_dims x_fid eq -1 then return'Please select the latitude band', $ if   y_fid eq -1 then return ; Figure out what UTM zone we're in. query_dims = [- lat_lon = [envi_get_data(fid=y_fid, dims=query_dims, pos=y_pos), $ 1L, long(dims[2]/2), long(dims[2]/2), long(dims[4]/2), long(dims[4]/2)] envi_get_data(fid=x_fid, dims=query_dims, pos=x_pos)] zone = south = (lat_lon[   fix(31.0 + lat_lon[1]/6.0)0] lt 0) ; Make the GLT. envi_file_query, fid, sname=sname out_name=sname+ pixel_size=[ rotation= i_proj = envi_proj_create(/geographic) o_proj = envi_proj_create(/utm, zone=zone) envi_glt_doit, i_proj=i_proj, $ o_proj=o_proj, out_name=out_name, $ pixel_size=pixel_size, r_fid=glt_fid, $ rotation=rotation, x_fid=x_fid, y_fid=y_fid, $ x_pos=x_pos, y_pos=y_pos '_glt'500.0D]0L if   glt_fid eq -1 then return ; Georeference the image from the GLT. out_name=sname+ envi_doit, glt_fid=glt_fid, out_name=out_name, pos=pos, $ subset=dims, r_fid=r_fid '_georef''envi_georef_from_glt_doit', fid=fid, $ end     [/QUOTE] compile_opt   pro