As part of a project, I need to be able to rebuild the Ubuntu alternate install ISO due to some of the requirements of the packages that need to be installed on the system. I've found the common pages about how to add packages to the alternate install discs (InstallCDCustomization), which I have managed to get to work, but it is becoming increasingly apparent that I may need to do more to the install image.

Because of this, what I really would like to find is documentation on how the alternate install image is created. Based on the research I've done, it appears to be based on the Ubuntu variant of the "debian-installer" package (instructions for building under Debian are here, and are roughly equivalent for Ubuntu after fetching the "debian-installer" source package), and... then I can't seem to find anything useful. I assume the process is similar to that of building a Debian install disc (instructions here), but I'm not entirely sure where the packages are pulled from, etc.

If anyone has any knowledge on this subject, even vague pointers would be appreciated, as I seem to have run into a blank wall of a lack of information. Thanks in advance!