The Layer Stacking tool in ENVI is really meant for situations where you want to stack different images that have different projections or pixel sizes or footprints into the same image. If your images already share all of those things, then you can just use the tool found under File > Save File As > ENVI Standard, to save a new version of the original file. To make that new version contain only some of the original bands, you would do it this way: 1. Choose File > Save File As > ENVI Standard. 2. In the New File Builder dialog that comes up, click the Import button. 3. In the resulting file selection dialog, select the original image, then click the Select By toggle button so that is says Select By Bands. You should now see all of the bands from the input file listed. Hold the Ctrl key, and select all of the bands that you want in the new file, then click OK in the file selection dialog. 4. Back in the New File Builder dialog, enter an output filename for the new 3-band file, then click OK. - Peg

Thanks Peg. The real problem is that I need to change the projection of my WV2 and Quickbird files from an RPC projection. Previously, I layer stacked the individual bands together and this change the RPC projection Geographic to just Geographic. I have a lot of images to process and it I was trying to find a way in IDL to do this.

It would be easy enough to alter your previous layer stacking routine to take just 3 bands of the same file using the POS keyword. However, using Layer Stacking to 'remove' the RPC projection could cause bad georeferencing for the file. An RPC projection is not a true map projection and converting it to a generic Geographic is not the same as georegistering the data to a true map projection. You should use the RPC Orthorectification on the data first to convert it to a true map projection (such as UTM) and then save out the 3 bands as Peg mentioned. Layer stacking is really not necessary for this case.

Thanks for the advice. Is there a script in IDL to do the RPC Orthorectification?