Getting absolute position of objects

[Dan Ringwalt]

Hello,

I found an old thread which was never answered: https://lists.gnu.org/archive/html/lilypond-user/2015-05/msg00860.html

I also need to output the absolute coordinates of all objects on the page, to generate training data for optical music recognition. I'm trying to print some information in \applyOutput, and I see that NoteHead X-offset and Y-offset are 0, and X-parent, Y-parent, X-positions, and Y-positions all seem to be (). Is there a way to get the absolute coordinates, so that I can add them to event-listener.ly?